3. โ Elements of High-Quality Image Production
โ CRT Gamma Characteristic
โ Light Level Definitions & HVS Light Perception
โ Dynamic Range Management in Camera
โ An Introduction to HDR Technology
โ Luminance and Contrast Masking and HVS Frequency Response
โ SMPTE ST-2084: โPerceptual Quantizerโ(PQ), PQ HDR-TV
โ ARIB STB-B67 and ITU-R BT.2100, HLG HDR-TV
โ Scene-Referred vs. Display-Referred and OOTF (Opto-Optical Transfer Function)
โ Signal Range Selection for HLG and PQ (Narrow and Full Ranges)
โ Conversion Between PQ and HLG
โ HDR Static and Dynamic Metadata
โ ST 2094, Dynamic Metadata for Color Volume Transforms (DMCVT)
Outline
3
4. โ Different HDR Technologies
โ Nominal Signal Levels for PQ and HLG Production
โ Exposure and False Color Management in HDR
โ Colour Bars For Use in the Production of HLG and PQ HDR Systems
โ Wide Color Gamut (WCG) and Color Space Conversion
โ Scene Light vs Display Light Conversions
โ Direct Mapping in HDR/SDR Conversions
โ Tone Mapping, Inverse Tone Mapping, Clipping and Color Volume Mapping
โ HDR & SDR Mastering Approaches
โ Color Representation for Chroma Sub-sampling
โ UHD Phases and HDR Broadcasting, Encoding and Transmission HDR
โ Different Log HDR-TV Standards
โ Sony S-Log3 HDR Standard
โ SR: Scene-referred and Super Reality (Scene Referred Live HDR Production) (SR Live Workflow )
Outline
4
9. โ๐ณ
๐ณ
= ๐ช๐๐๐๐๐๐๐ (โ ๐. ๐๐)
Masker: Background ๐ณ๐ (one stimulus)
Disk: Another stimulus ๐ณ๐ + โ๐ณ๐
In the brighter parts of an image
โ๐ณ
๐ณ
= ๐ช๐๐๐๐๐๐๐ (โ ๐. ๐๐)
Masker: Background ๐ณ๐(one stimulus)
Disk: Another stimulus ๐ณ๐ + โ๐ณ๐
In the dark parts of an image
Masker: Background ๐ณ๐(one stimulus)
Disk: Another stimulus ๐ณ๐ + โ๐ณ๐
โ๐ณ๐ = ๐ถ๐๐ณ๐
โ๐ณ๐ = ๐๐๐ณ๐
Masker: Background ๐ณ๐(one stimulus)
Disk: Another stimulus ๐ณ๐ + โ๐ณ๐
โ๐ณ๐ > โ๐ณ๐ โ๐ณ๐ > โ๐ณ๐
๐ถ๐ > ๐ถ๐
Weber-Fechner law and De Vries-Rose law
๐ถ๐ = ๐ถ๐ โ ๐. ๐๐
โ๐ณ๐ = ๐ถ๐๐ณ๐
โ๐ณ๐ = ๐๐๐ณ๐
โ๐ฟ
๐ฟ
= ๐ช (โ ๐. ๐๐)
โ๐ฟ
๐ฟ
= ๐พ
โ๐ฟ
๐ฟ
=
๐พ
๐ฟ
9
10. Weber-Fechner law
Weber Fraction
โL/L, Linear scale
Background Luminance, L (millilamberts), Log scale
โ๐ณ
๐ณ
= ๐ช๐๐๐๐๐๐๐ (โ ๐. ๐๐)
In โ๐ณ, the object can be noticed by the HVS with a 50% chance.
Masker: Background ๐ณ (one stimulus)
Disk: Another stimulus ๐ณ + โ๐ณ
In the brighter parts of an image
Minimum Detectable Contrast
โ๐ฟ
๐ฟ
= ๐ช๐๐๐๐๐๐๐ (โ ๐. ๐๐)
โ๐ณ ๐๐ ๐ ๐๐๐๐๐๐๐๐ ๐๐๐๐๐๐๐๐๐๐ ๐๐ ๐ณ
10
11. Weber-Fechner law
โ The Weber-Fechner law is a classical representation of contrast sensitivity.
โ According to this law, the minimum detectable contrast, i.e. the reciprocal of contrast sensitivity, is
constant regardless luminance.
โ It is believed that the ratio is between 1/50 and 1/100. However, it increases below and above certain
luminances.
โ In the brighter parts and highlights of an image the threshold for perceiving quantization error (banding or
contouring) is approximately constant, so quantization distortion visibility is constant.
Minimum Detectable Contrast
โ๐ฟ
๐ฟ
= ๐ช๐๐๐๐๐๐๐ (โ ๐. ๐๐)
โ๐ณ ๐๐ ๐ ๐๐๐๐๐๐๐๐ ๐๐๐๐๐๐๐๐๐๐ ๐๐ ๐ณ
11
12. De Vries-Rose law, (Hessel de Vries, Albert Rose)
De Vries-Rose law
โ In the low lights it becomes increasingly difficult to perceive banding.
โ That is, the threshold of visibility for banding becomes higher as the image gets darker.
โ It means for small values of ๐ณ, with decreasing the ๐ณ, โ๐ณ is increased and is more percentage of
background luminance L.
โ Note that for two values ๐ณ๐ < ๐ณ๐ โ โ๐ณ๐< โ๐ณ๐ because โ๐ณ = ๐ฒ ๐ณ.
.
โ๐ฟ
๐ฟ
= ๐พ ๐ฟ โ โ๐ฟ ๐๐ ๐๐๐๐ ๐๐๐๐๐๐๐ก๐๐๐ ๐๐ ๐ฟ
โ
โ๐ฟ
๐ฟ
=
๐พ
๐ฟ
12
13. log10 โ๐ฟ = log10 ๐ถ + log10 ๐ฟ
โ๐ณ
๐ณ
= ๐ช
โ๐ณ
๐ณ
= ๐ฒ log10 โ๐ฟ = log10 ๐พ +
1
2
log10 ๐ฟ
โ
โ
L (millilamberts), Log scale
Threshold
โL (millilamberts), Log scale
Slope=1
Slope=1/2
Weber-Fechner law and De Vries-Rose law
13
14. Contrast Sensitivity
โ This graph is redrawn from Schreiberโs Fundamentals of Electronic Imaging Systems.
At very low luminance values, the curve departs from logarithmic
behaviour and approximates a square-root; this characteristic is
called the de Vries-Rose law (Hessel de Vries, Albert Rose).
The flat portion of the curve shows that the
perceptual response to luminance โ termed
lightness โ is approximately logarithmic.
โ๐ณ
๐ณ
= ๐ช โ ๐. ๐๐
Slope=0.5
The transition occurs between absolute
luminance values of 0.1 to 1 nt.
(0.025)
(0.0158)
(0.039)
(0.063)
(0.1)
(0.158)
(
โ๐ณ
๐ณ
)
Quantization Effects (Banding): The Schreiber Threshold
โ๐ณ
๐ณ
= ๐ฒ
Over a range of luminance values of about
300:1, the discrimination threshold of vision is
approximately a constant ratio of luminance. ๐บ =
๐
๐ช๐๐๐
๐ช๐๐๐ =
โ๐ณ๐๐๐
๐ณ
14
15. 0.03
0.02
0.01
0
0.04
0.05
0.06
0.07
0.08
0.1
0.09
0.01 0.1 100 1000 10000
Weber
Fraction
1 10
Display Luminance cd/mยฒ
Schreiber
De Vries-Rose Law
Critical Contrast โ๐ณ = ๐ฒ ๐ณ
WeberโFechner Law
Critical Contrast โ๐ณ = ๐ช๐ณ โ ๐. ๐๐๐ณ
Quantization Effects (Banding): The Schreiber Threshold
โ๐ณ
๐ณThe actual CSF varies with the screen luminance, field of view, spatial frequency of the
image, etc. Bartenโs model takes such conditions into account.
15
16. 100
Minimum Detectable Contrast (%)
Minimum Contrast Step (%)
L: Luminance (nit)
Contouring
(Banding)
โ๐ณ
๐ณ
ร100
Above Threshold
โข Step edges are visible
โข Visible contouring/banding
Below Threshold
โข Step edges are invisible
โข Smooth gradients
Barten Ramp
โข ITU-R Report BT.2246
โข Consensus threshold of human
visibility for normal images
โ๐ณ & L are Large โ Less bits are required โ
Larger quantize step size
โ๐ณ & L are small โ More bits are required โ
Smaller quantize step size
โ๐ณ
๐ณ
ร100
โ๐ณ
๐ณ
ร100
Barten Ramp
In the dark areas, the
threshold of visibility
for banding becomes
higher as the image
gets darker.
โข The Barten Ramp is an extremely handy graph that plots out where most people can begin
to see banding in a gradient (ie, the steps between each shade, (๐ณ to ๐ณ + โ๐ณ is perceivable
or not)) when mapping out all the way to 10,000 nits for potential HDR imagery.
โข The area in green shows where no banding can be seen but the area in red shows where
banding can be seen and is therefore problematic.
Contouring
(Banding)
De Vries-Rose Law
Critical Contrast โ๐ณ = ๐ฒ ๐ณ
WeberโFechner Law
Critical Contrast โ๐ณ = ๐ช๐ณ โ ๐. ๐๐๐ณ
๐ณ โโ โ๐ณ ๐๐ ๐๐๐๐ ๐๐๐๐๐๐๐๐๐๐ ๐๐ ๐ณ โ๐ณ ๐๐ ๐ ๐๐๐๐๐๐๐๐ ๐๐๐๐๐๐๐๐๐๐ ๐๐ ๐ณ
16
The threshold for
perceiving banding is
approximately constant
in the brighter parts and
highlights of an image.
17. Above Threshold
โข Step edges are visible
โข Visible contouring/banding
Below Threshold
โข Step edges are invisible
โข Smooth gradients
Barten Ramp
โข ITU-R Report BT.2246
โข Consensus threshold of human
visibility for normal images
100
Minimum
Contrast
Step
(%)
Luminance (nit)
โ๐ณ
๐ณ
ร
100
SDR (LCD, BT. 1886 Gamma)
The experience has shown that with realistic
camera noise levels, the slight quantization
artefacts predicted for 100 nits ITU-R BT.1886
are masked and thus do not present real
problems in television production.
BT. 1886 Performance in 8-Bit, 10-Bit and 15-bit for SDR
Optical
Electronic
OETF
(Camera Gamma)
How many bits is required for
avoiding banding effect?
17
18. Above Threshold
โข Step edges are visible
โข Visible contouring/banding
Below Threshold
โข Step edges are invisible
โข Smooth gradients
Barten Ramp
โข ITU-R Report BT.2246
โข Consensus threshold of human
visibility for normal images
100
Minimum
Contrast
Step
(%)
Luminance (nit)
โ๐ณ
๐ณ
ร
100
HDR
BT. 1886 Performance in 12-Bit and 15-bit for HDR
Optical
Electronic
OETF
(Camera Gamma)
How many bits is required for
avoiding banding effect?
It
waste
bits
in
bright
regions
Banding
18
19. Sensitivity of the HVS to Potential Gamma Levels
โ Levels below this dashed line are invisibly small to humans and levels above the line are potentially visible
โ Lines above the threshold curve may exhibit visual artefacts, so traditional gamma is not OK for HDR.
EOTF used by todayโs TV
systems, with 8-bit quantization
Result of extending traditional gamma
curve to a 10-bit gamma EOTF
EOTF used by todayโs TV systems,
with 10-bit quantization..
SMPTE 10-bit: One of the
proposals for an EOTF that
has a better match over HDR
The dashed line shows the limit of human ability to
detect steps in luminance levels.(Bartens
Threshold: (L to L+dL is perceivable or not))
Luminance levels
19
20. Perceptual Quantizer (PQ) Electro-Optical Transfer Function (EOTF)
Code words are equally spaced in perceived brightness over this range of luminance.
Equally
Spaced
Code
Words
(10
bits)
Standardized as SMPTE ST-2084 and ITU-R BT.2100 (10 bit)
PQ HDR Display
Perceived Brightness
๐ญ๐ซ: Display Luminance
๐น๐ท=EOTF[๐ธโฒ
]=10000 Y
๐ธโฒ
๐1 = 0.1593017578125
๐2= 78.84375
๐1= 0.8359375
๐2= 18.8515625
๐3= 18.6875
๐ =
max แ
๐ธ
1
๐2 โ ๐1 , 0
๐2 โ ๐3
แ
๐ธ
1
๐2
1
๐1
๐ฌโฒ (video level) denotes a non-linear
colour value {๐นโฒ, ๐ฎโฒ, ๐ฉโฒ} or { ๐ณโฒ, ๐ดโฒ, ๐บโฒ} in
PQ space in the range [0:1]
๐น๐ท
20
21. Code Levels Distribution in HDR
Uniform (equally spaced) Code Words for Perceived Brightness
Perceived Brightness
21
22. Code Levels Distribution in HDR
Uniform (equally spaced) Code Words for Perceived Brightness
More Code Words
for Dark Area
Less Code Words for
Bright Area
Perceived Brightness
22
23. Code Words Utilization by Luminance Range in PQ
โข PQ headroom from 5000 to 10,000
nits = 7% of code space
โข 100 nits is near the midpoint of the
code range
23
24. 4 129 254 379 504 629 754 879 1019
10000
9000
8000
7000
6000
5000
4000
3000
2000
1000
0
๐๐/๐ฆ๐
10 Bit Code Value
PQ Display Luminance Defined by Absolute Code Value
Display-referred
Image Data
SMPTE ST 2084
PQ 10K EOTF
Display Peak Luminance= 10000 nits
The PQ curveโs maximum brightness is always mapped to the
maximum brightness of the reference display to ensure the highest
fidelity if the reference and consumer display have similar properties.
4000 nits
2000 nits
3000 nits
1000 nits
24
25. 10000
9000
8000
7000
6000
5000
4000
3000
2000
1000
0
๐๐/๐ฆ๐
PQ Display Luminance Defined by Absolute Code Value
Display Peak Luminance= 10000 nits
12 Bit Code Value: 16 516 1016 1516 2016 2516 3016 3516 4079
10 Bit Code Value: 4 129 254 379 504 629 754 879 1019
8 Bit Code Value: 1 32 64 95 126 157 189 220 255
SMPTE ST 2084
PQ 10K EOTF
4000 nits
2000 nits
3000 nits
1000 nits
Display-referred
Image Data
The PQ curveโs maximum brightness is always mapped to the
maximum brightness of the reference display to ensure the highest
fidelity if the reference and consumer display have similar properties.
25
26. 4 129 254 379 504 629 754 879 1019
1000
900
800
700
600
500
400
300
200
100
0
SMPTE ST 2084
๐๐/๐ฆ๐
PQ 1K EOTF
10 Bit Code Value
4 129 254 379 504 629 754 879 1019
4000
3600
3200
2800
2400
2000
1600
1200
800
400
0
SMPTE ST 2084
๐๐/๐ฆ๐
PQ 4K EOTF
10 Bit Code Value
Display-referred
Image Data
Display Peak Luminance= 1000 nits Display Peak Luminance= 4000 nits
โ The PQ curveโs maximum brightness is always mapped to the maximum brightness of the reference display
to ensure the highest fidelity if the reference and consumer display have similar properties.
PQ Display Luminance Defined by Absolute Code Value
26
27. Perceptual Quantizer (PQ) Electro-Optical Transfer Function (EOTF) on Barten Ramp
Optical
Electronic
OETF
(Camera Gamma)
How many bits is required for
avoiding banding effect?
Visible Difference between shades resulting in banding
Smooth gradient with no discernable difference between shades
โ๐ณ
๐ณ
ร
100
Minimum
Contrast
Step
(%)
Luminance (nit)
27
29. 12 Bit PQ โ Puts Levels Where They are Needed
(4096 Levels)
29
30. BT.1886 and PQ Performances in 10-Bit for HDR
Minimum
Contrast
Step
(%)
Display luminance (cd/๐๐
)
โ Result of extending existing
(traditional) gamma BT.1886 curve
to a 10-bit gamma EOTF (without
any change to the value of
gamma)
โ BT. 1886 EOTF used by todayโs TV
systems, with 10-bit quantization
10 bit PQ 10,000 nit
Large Contrast Step Small Contrast Step
โ๐ณ
๐ณ
ร
100
30
31. BT.1886 and PQ Performances in 12-Bit for HDR
12 bit PQ 10,000 nit
โ Result of extending existing
(traditional) gamma BT.1886 curve
to a 12-bit gamma EOTF (without
any change to the value of
gamma)
โ BT. 1886 EOTF used by todayโs TV
systems, with 12-bit quantization
Large Contrast Step Small Contrast Step
โ๐ณ
๐ณ
ร
100
Display luminance (cd/๐๐
)
Minimum
Contrast
Step
(%)
31
32. OpenEXR Raster Image Format
โ OpenEXR: Open Extended Dynamic Range
โ It is an open source image format created by Industrial Light and Magic with the purpose of being used as
an image format for special effects rendering and compositing.
โ The format is a general purpose wrapper for the 16 bit half-precision floating-point data type, Half.
โ The Half format, or binary16, is specified in the IEEE 754-2008 standard.
โ OpenEXR also supports other formats such as both floating-point and integer 32 bit formats. Using the Half
data type the format will have 16 bits per channel, or 48 bits per pixel.
โ The OpenEXR format is able to cover the entire visible gamut and a range of about 10.7 orders of
magnitude with a relative precision of 0.1%.
โ Based on the fact that the human eye can see no more than 4 (or 5) orders of magnitude simultaneously,
OpenEXR makes for a good candidate for archival image storage.
32
33. PQ: Most efficient use of bits
throughout entire range with
precision below threshold of
visibility
SMPTE ST-2084: โPerceptual Quantizerโ(PQ)
EXR: Well below Barten threshold = Invisible contrast steps
โ๐ณ
๐ณ
ร
100
33
34. Design of the PQ Non-Linearity
Barten Ramp: 10-bit Quantization Noise visibility @ 0.01 โ 1000 Nits
Contouring
โ Though the signal lines all come above the threshold curve to some
extent, experience has shown that with realistic camera noise levels,
the slight quantization artefacts predicted for 100 nits ITU-R BT.1886 or
10000 nits PQ are masked and thus do not present real problems in
television production.
Larger Contrast Step Size Smaller Contrast Step Size
Minimum
Contrast
Step
(%)
Display luminance (cd/๐๐
)
โ๐ณ
๐ณ
ร
100
WeberโFechner Law
Critical Contrast or โ๐ณ = ๐ช๐ณ โ ๐. ๐๐๐ณ
2
34
35. Design of the PQ Non-Linearity
Barten Ramp: 12-bit Quantization Noise visibility @ 0.001 โ 1000 Nits
โ In PQ can be shown 0.00005 up to 10000 nits (~27.6 Stop).
โ Lines which fall below Barten curve will not exhibit any visible
quantization artefacts (such as image banding).
โ Lines above the Barten curve may exhibit visual artefacts
Display luminance (cd/๐๐
)
Minimum
Contrast
Step
(%)
โ๐ณ
๐ณ
ร
100
Larger Contrast Step Size Smaller Contrast Step Size
2
WeberโFechner Law
Critical Contrast or โ๐ณ = ๐ช๐ณ โ ๐. ๐๐๐ณ
35
36. 12 bit uniform JND curves
Code words are equally spaced in perceived brightness over Luminance
JNDs Based on Barten Model
โ Human perceptible units called โJust Noticeable Differenceโ (JND); 1JND=the minimum noticeable difference for human.
โ Uniform JND: When bit depth is limited, the code words are distributed evenly over perceived brightness and errors are
minimized.
โ By this approach, there are less code values wasted to encode sub JND steps in areas where JNDs are larger
โ๐ณ
๐ณ
ร
100
WeberโFechner Law
Critical Contrast or โ๐ณ = ๐ช๐ณ โ ๐. ๐๐๐ณ
36
37. JNDs Based on Barten Model
๐ถ๐๐น(๐ข)
Barten Parameters Chosen Conservatively
I. 40ยบ angular size
II. Varied spatial frequency at every luminance level to track peaks of the CSF (Contrast Sensitivity Function)
III. Select peak luminance level
IV. Iteratively calculate the rest of the steps
37
38. JNDs Based on Barten Model
๐ถ๐๐น(๐ข)
Barten Parameters Chosen Conservatively
I. 40ยบ angular size
II. Varied spatial frequency at every luminance level to track peaks of the CSF (Contrast Sensitivity Function)
III. Select peak luminance level
IV. Iteratively calculate the rest of the steps
38
39. ๐๐๐๐ข๐๐๐ก๐๐๐ ๐โ๐๐๐ โ๐๐๐ ๐๐ก โ 1
๐ถ๐๐น ๐ข
Also
๐๐๐๐ข๐๐๐ก๐๐๐ ๐โ๐๐๐ โ๐๐๐ ๐๐ก=
๐ฟ๐๐๐ฅโ๐ฟ๐๐๐
๐ฟ๐๐๐ฅโ๐ฟ๐๐๐
Once we know the sensitivity CSF(u), we also know the modulation threshold
๐ฟ๐๐ฃ๐๐๐ ๐ฟ๐+1 = ๐ฟ๐
1+๐.๐๐ก
1โ๐.๐๐ก
Choose peaks of 100, 1000, and 10,000 nits as before
Then pick ๐ so that a near zero minimum level is reached
(Pick JND fraction ๐ such that a near-zero bottom level is reached at the other end of the range)
โ 0 to 100 nits, ๐ = ๐. ๐๐ JNDs per code word at 12 bits
โ 0 to 1000 nits, ๐ = ๐. ๐๐ JNDs per code word at 12 bits
โ 0 to 10,000 nits, ๐ = ๐. ๐ JNDs per code word at 12 bits
JNDs Based on Barten Model
Merging with pick JND fraction, ๐
Barten Parameters Chosen Conservatively
I. 40ยบ angular size
II. Varied spatial frequency at every luminance level to track peaks of the CSF (Contrast Sensitivity Function)
III. Select peak luminance level
IV. Iteratively calculate the rest of the steps
39
40. Generalized OOTF from ITU-R BT.1886 in Combination with ITU-R BT.709
โ We want the image from an SDR source and that from an HDR source to match everywhere the HDR
image brightness overlaps the range of the SDR source (i.e. for less than 100 nits).
โ In order to maximize compatibility with existing SDR signals, it is desired an OOTF consistent with the
effective OOTF of existing practice which is:
โ This maximizes compatibility for mixed source applications wherein some sources are HDR and some are
SDR.
SDR Signal
PQ HDR Signal
with less than 100 nits
luminance
โข It maximize compatibility for PQ
HDR content less that 100 nits.
โข It emulates the โlookโ of ITU-R
BT.709 plus ITU-R BT.1886 for
display light up to the limit of SDR
SDR Display
PQ HDR Display
๐๐๐๐น๐๐ท๐ = ๐ธ๐๐๐น1886[๐๐ธ๐๐น709]
PQ HDR Signal
(up to 10000 nits)
40
41. Generalized OOTF from ITU-R BT.1886 in Combination with ITU-R BT.709
โ It is only needed to extend the range of ๐ถ๐ฌ๐ป๐ญ๐๐๐ and ๐ฌ๐ถ๐ป๐ญ๐๐๐๐ for HDR.
โ The extension factor for displayed light is 100.
โ As the SDR OOTF has a roughly gamma = 1.2 characteristic at the high end, the extension relative to scene
light (the input to OOTF) is approximately
โ It means that if we extend SDR OOTF for getting 10000 nits output, then the extension factor for the linear
scene light is about 46.42.
โ For creating ๐บ709, the ๐ธ๐๐ท๐ should be replace by 59.5208๐ธ๐๐ท๐ in ๐ถ๐ฌ๐ป๐ญ๐๐๐ because ๐ธ๐ป๐ท๐ = 59.5208๐ธ๐๐ท๐
(๐ธ๐น๐)๐พ
= ๐ธ๐น๐ท
๐ธ๐น๐ท =
๐ฟ๐ป๐ท๐
๐ฟ๐๐ท๐
=
10000
100
= 100
๐ธ๐น๐ = 100(
1
1.2
)
= 46.42.
When the exact equations for ITU-R BT.709 and BT.1886 are used, the extension for HDR is 59.5208.
41
42. Generalized OOTF from ITU-R BT.1886 in Combination with ITU-R BT.709
โ To expand the range of ๐๐ธ๐๐น709 to ๐บ709 for HDR the equation is therefore:
โ Note: HDR E is normalized to range of 0 to 1
โ Consequently, the range of ๐ฌโฒ is [๐, ๐. ๐๐๐] for HDR while it remains [0,1] for SDR.
๐ฌ = ๐ โ ๐ธโฒ
= 6.813
๐ฌ =
๐
๐๐. ๐๐๐๐
โ ๐ธโฒ
= 1
๐ฌ = ๐ โ ๐ธโฒ
= 0
๐ธโฒ = ๐บ709 ๐ธ =
1.099(59.5208๐ธ)0.45 โ 0.099
0.018
59.5208
< ๐ธ < 1
4.5(59.5208๐ธ) 0 < ๐ธ <
0.018
59.5208
๐ธโฒ
= ๐บ709 ๐ธ = แ1.099(59.5208๐ธ)0.45 โ 0.099 0.0003024 < ๐ธ < 1
267.84๐ธ 0 < ๐ธ < 0.0003024
๐ = ๐บ709 ๐ฟ = เต
1.099(๐ฟ)0.45 โ 0.099 0.018 < ๐ฟ < 1
4.5(๐ฟ) 0 < ๐ฟ < 0.018
๐ฟ : luminance of the image 0 <๐ฟ< 1
๐ : corresponding electrical signal
SDR OETF, ๐ถ๐ฌ๐ป๐ญ๐๐๐
Extended SDR OETF, ๐ฎ๐๐๐
HDR
SDR
42
43. Generalized OOTF from ITU-R BT.1886 in Combination with ITU-R BT.709
โ To expand the range of ๐ธ๐๐๐น1886 to ๐บ1886 for HDR no change to the equation is necessary, the argument is
simply allowed to extend to 6.813 and hence the range increases from 100 to 10 000:
โ These extensions satisfy the boundary conditions:
๐ฌ = ๐ โ ๐ธโฒ
= 6.813 โ A displayed luminance of 10 000 cd/mยฒ
๐ฌ =
๐
๐๐.๐๐๐๐
โ ๐ธโฒ
= 1 โ A displayed luminance of 100 cd/mยฒ
FD = G1886[E'] = 100 Eโฒ 2.4
FD = OOTF[E] = G1886 [G709[E]] =G1886 [Eโฒ] = 100๐ธโฒ2.4
๐ธโฒ
= ๐บ709 ๐ธ = แ1.099(59.5208๐ธ)0.45
โ 0.099 0.0003024 < ๐ธ < 1
267.84๐ธ 0 < ๐ธ < 0.0003024
๐ณ = ๐(๐ฆ๐๐ฑ ๐ฝ + ๐ , ๐ )๐ธ
๐ฌ๐ถ๐ป๐ญ๐๐๐๐ ๐ฎ๐๐๐๐
The extension factor for
displayed light is 100.
๐ณ = (๐ฝ)๐ธ
43
44. Generalized OOTF from ITU-R BT.1886 in Combination with ITU-R BT.709
โ The x-axis, is the same as ๐ฌ for SDR while for HDR it is ๐๐. ๐๐๐๐๐ฌ since the domain of ๐ฌ is [0,1]:
OOTF[E] = G1886 [G709[E]]
โข OETF709 is expanded to G709 for HDR
โข EOTF1886 is expanded to G1886 for HDR
๐ถ๐ถ๐ป๐ญ๐บ๐ซ๐น = ๐ฌ๐ถ๐ป๐ญ๐๐๐๐[๐ถ๐ฌ๐ป๐ญ๐๐๐]
๐ถ๐ถ๐ป๐ญ๐ฏ๐ซ๐น = ๐ถ๐ฌ๐ป๐ญ๐ท๐ธ ร ๐ฌ๐ถ๐ป๐ญ๐ท๐ธ
FD
E
๐ฌ =
๐
๐๐. ๐๐๐๐
ยฐ
44
45. Actual OOTFs from Manually Graded Content
Comparison of proposal OOTF with the actual OOTFs by
manually grading camera RAW output:
โ The OOTF is the ratio of the graded linear output to
the RAW linear input.
โ Figure shows several examples from the HDR
sequence โFantasy Flightsโ:
โ These Figures show:
โข Scatter plots of the log of the output luminance derived
from the PQ grade
versus
โข The log of the relative input luminance derived from the
ARRI RAW camera output
For comparison, the OOTF from the
combination of Recommendations ITU-R
BT.1886 and BT.709 are plotted in white.
These scatter plots are colour-coded (RGB) to match the
images shown in the lower right corner of each figure.
Toe
45
46. Actual OOTFs from Manually Graded Content
โ This shows that the extracted OOTFs are, as one
would expect, a bit brighter than SDR.
โ Some preliminary conclusions can be drawn from
this experimental data:
1. For this manually graded content, the OOTF is
not a straight line, and thus the actual OOTF
does not correspond to an overall โsystem
gammaโ.
2. Darker indoor scenes tend to be noise limited at
the bottom end and the OOTF exhibits a very
clear toe.
3. The extracted OOTFs appear to have roughly
the same curvature in the mid-tones as the
proposed model.
For comparison, the OOTF from the
combination of Recommendations ITU-R
BT.1886 and BT.709 are plotted in white.
These scatter plots are colour-coded (RGB) to match the
images shown in the lower right corner of each figure.
Toe
46
47. Resultant PQ OETF from Generalization
โ OOTF can be combined with the
inverse of the EOTF to produce an OETF.
โ In actual cameras, there is noticeable
noise at low signal levels, and in
practice the OETF slope at low levels is
limited so as to โcrushโ the noise in
black, thereby putting a โtoeโ into the
response.
โ The reference OETF does not have such
a โtoeโ, but one is apparent in the
OOTF plot for the indoor scene of
โFantasy Flightsโ shown above.
Toe
โข It imulates the โlookโ of ITU-R BT.709 plus ITU-R BT.1886 for display light
up to the limit of SDR
โข It Facilitates mixing of legacy ITU-R BT.709 signals and PQ HDR signals
โข It Offers reasonable behavior for levels above those of SDR.
OETFPQ, Camera = OOTFPQ, Camera ร EOTF โ๐
PQ, Camera
๐ฌ ๐ฌโฒ
PQ encoded
color value
The signal determined
by scene linear light
Scene
Light
OOTF
PQ
๐ฌ๐ถ๐ป๐ญโ๐
PQ OETF
47
48. The PQ HDR system generates content that is optimum for viewing on
I. A Reference Monitor
โข 0.005 nits up to 10 000 nits, capable of showing the entire color gamut
II. A Reference Viewing Environment
โข The viewing environment would ideally be dimly lit, with the area surrounding the monitor being a neutral grey
(6500 degree Kelvin) at a brightness of 5 nits.
Why Display Mapping (DM)
โ Content often must be viewed or produced in environments brighter than the reference condition, and on
monitors that cannot display the deepest blacks or brightest highlights that the PQ signal can convey.
โ Display Mapping can take the form of an EETF (Electrical-electrical Transfer Function) in the display.
Display Mapping and EETF (Electrical-electrical Transfer Function)
Scene
Light
OOTF
PQ
EOTF-1
EETF EOTF
Display
Light
PQ signal
48
49. This functions provide a toe and knee to gracefully roll off
the highlights and shadows providing a balance between
preserving the artistic intent and maintaining details.
Toe
Knee
EETF EOTF
Display
Light
PQ signal
Display Mapping and EETF (Electrical-electrical Transfer Function)
To โcrushโ the
noise in black,
49
50. Artistic OOTF
โข If an artistic image โlookโ different from that produced by the reference OOTF is
desired, โArtistic adjustโ may be used.
โข An artistic adjustment may be used to further modify the creative intent of the image
The PQ EOTF replaces the BT.1886 function
of SDR HDTV, and the corresponding PQ
OETF replaces the BT.709 OETF as the
default camera capture curve.
A display adjustment is used to adapt the signal for
different display characteristics and display environments.
PQ HDR-TV system Architecture
No use of metadata is shown or required.
Camera
Sensor
Image
Display
Adjust
Creative
Intent
PQ
EOTF
PQ
EOTF
Reference
OOTF
Artistic
Adjust
PQ
EOTF โ๐
PQ OETF
50
51. Reference OOTF = OETF (PQ) + EOTF (PQ)
โ Opto-Electronic Transfer Function (OETF): Scene light to electrical signal
โ Electro-Optical Transfer Function (EOTF): Electrical signal to scene light
OOTF (Opto-Optical Transfer Function)
PQ OETF PQ EOTF
๐ฌ: [๐, ๐] ๐ฌโฒ
: [๐, ๐]
๐ญ๐ซ
Linear Scene-light
Signals ๐น๐, ๐ฎ๐, ๐ฉ๐
Non-linear
Signals ๐น๐, ๐ฎ๐, ๐ฉ๐
Linear Display-light
Signals ๐น๐ซ, ๐ฎ๐ซ, ๐ฉ๐ซ
๐ญ๐บ
51
52. โ Opto-Electronic Transfer Function (OETF): Scene light to electrical signal
โ Electro-Optical Transfer Function (EOTF): Electrical signal to scene light
OOTF (Opto-Optical Transfer Function)
PQ OETF PQ EOTF
๐ฌ: [๐, ๐] ๐ฌโฒ
: [๐, ๐]
Linear Scene-light
Signals ๐น๐, ๐ฎ๐, ๐ฉ๐
Non-linear
Signals ๐น๐, ๐ฎ๐, ๐ฉ๐
Linear Display-light
Signals ๐น๐ซ, ๐ฎ๐ซ, ๐ฉ๐ซ
Non linear color value,
encoded in PQ space in
the range [0,1].
The signal determined by scene
linear light, scaled by camera
exposure in the range [0:1].
๐ญ๐ซ :The luminance of a displayed linear
component {๐น๐ซ, ๐ฎ๐ซ, ๐ฉ๐ซ} or ๐๐ซ or ๐ฐ๐ซ, in cd/mยฒ.
The luminance of a single colour component (๐น๐ซ, ๐ฎ๐ซ,
๐ฉ๐ซ), means the luminance of an equivalent achromatic
signal with all three colour components having that
same value.
๐ญ๐ซ
๐ญ๐บ
52
53. โ There are different type of signal formats; ๐ ๐บ๐ต, ๐๐ถ๐๐ถ๐ and ๐ผ๐ถ๐๐ถ๐.
โ ๐ญ๐ซ is the luminance of a displayed linear component {๐น๐ซ, ๐ฎ๐ซ, ๐ฉ๐ซ} or ๐๐ซ or ๐ฐ๐ซ, in cd/mยฒ.
โ The luminance of a single colour component (๐น๐ซ, ๐ฎ๐ซ, ๐ฉ๐ซ ), means the luminance of an equivalent
achromatic signal with all three colour components having that same value.
OOTF (Opto-Optical Transfer Function)
Equivalent Achromatic Signal Equivalent Achromatic Signal Equivalent Achromatic Signal
๐โฒ
= 0.2126๐ โฒ
+ 0.7152๐บโฒ
+ 0.0722๐ตโฒ
๐ = 0.2126๐ + 0.7152๐ + 0.0722๐ ๐ = 0.2126๐บ + 0.7152๐บ + 0.0722๐บ ๐ = 0.2126๐ต + 0.7152๐ต + 0.0722๐ต
53
54. To display HDR accurately, same settings between OETF of camera and EOTF of display are needed!!
--> Different settings make HDR signal and display to look wrong
Linear Scene Light
Cancel
OOTF=Artistic Intent
(seasoning)
EOTF-1
OOTF
Input [%]
Output
[cd/ใก ]
Camera Monitor
Display Light
OETF
Optical Signal
Scene Light
Electronic Signal
EOTF
OOTF Position in PQ
Display-Referred Signal
Output [%]
Input [cd/ใก ]
Display Linear Light
54
55. To display HDR accurately, same settings between OETF of camera and EOTF of display are needed!!
--> Different settings make HDR signal and display to look wrong
Linear Scene Light
Cancel
OOTF=Artistic Intent
(seasoning)
EOTF-1
OOTF
Input [%]
Output
[cd/ใก ]
Camera Monitor
Display Light
OETF
Optical Signal
Scene Light
Electronic Signal
EOTF
OOTF Position in PQ
Display-Referred Signal
Output [%]
Input [cd/ใก ]
Display Linear Light
The PQ system specifies a display-referred HDR signal which means that the PQ signal describes the
absolute output light from the mastering display.
โข Therefore, the mastering display EOTF transfer characteristics is implemented in the display and the
signal produced by the camera is dependent to the mastering display.
โข That means that there is additional processing and metadata are required to convert the signal for a
particular screen.
55
56. PQ End to End Chain + Metadata
๐ฌ ๐ฌโฒ
๐ญ๐ซ
Non linear color value, encoded
in PQ space in the range [0,1].
The signal determined
by scene linear light, scaled by
camera exposure in the range [0:1]. The luminance of a displayed linear
component {๐น๐ซ, ๐ฎ๐ซ, ๐ฉ๐ซ} or ๐๐ซ or ๐ฐ๐ซ.
Scene
Light
OOTF
PQ
๐ฌ๐ถ๐ป๐ญโ๐
Display-referred
Image Data
PQ OETF
PQ
EOTF
Display
Light
Decoding
Camera
Encoding
Mastering Display
E = {๐น๐, ๐ฎ๐, ๐ฉ๐, ๐๐, or ๐ฐ๐}: The signal determined by scene linear light and scaled by camera exposure in the range [0:1].
Eโ= {R', G', B'} or { L', M', S'}: A non-linear PQ encoded color value in PQ space in the range [0,1].
๐ญ๐ซ: The luminance of a displayed linear component {๐น๐ซ, ๐ฎ๐ซ, ๐ฉ๐ซ} or ๐๐ซ or ๐ฐ๐ซ, in cd/mยฒ.
โข The luminance of a single colour component (๐ ๐ท, ๐บ๐ท, ๐ต๐ท), means the luminance of an equivalent achromatic signal
with all three colour components having that same value.
56
57. PQ End to End Chain + Metadata
๐ฌ ๐ฌโฒ
Non linear color value, encoded
in PQ space in the range [0,1].
The signal determined
by scene linear light, scaled by
camera exposure in the range [0:1].
Scene
Light
OOTF
Display-referred
Image Data
PQ OETF
PQ
EOTF
Display
Light
Decoding
Camera
Encoding
Mastering Display
Display
Light
Display Adjustment
Other Display and Environments
OOTF
Adjust
PQ
EOTF
Decoding
Optional
Metadata
PQ
๐ฌ๐ถ๐ป๐ญโ๐
Metadata is needed for
display adjustment
The luminance of a displayed linear
component {๐น๐ซ, ๐ฎ๐ซ, ๐ฉ๐ซ} or ๐๐ซ or ๐ฐ๐ซ.
๐ญ๐ซ
57
58. ๏ ๏
๏จ ๏ฉ
๏ ๏ 1
2
2
1
1
3
2
1
1
0
,
max
10000
EOTF
m
m
m
D
E
c
c
c
E
Y
Y
E
F
๏ท
๏ท
๏ธ
๏ถ
๏ง
๏ง
๏จ
๏ฆ
๏ข
๏ญ
๏ญ
๏ข
๏ฝ
๏ฝ
๏ข
๏ฝ
Parameter Values
Input signal to PQ electro-optical transfer
function (EOTF)
๐ฌโฒ : Non-linear PQ encoded value.
The EOTF maps the non-linear PQ signal into display light.
Reference PQ EOTF 4a
(Note 4a โ This same non-linearity (and its
inverse) should be used when it is necessary to
convert between the non-linear representation
and the linear representations.)
(Note 4b โ In this Recommendation, when
referring to the luminance of a single colour
component (๐ ๐ท, ๐บ๐ท, ๐ต๐ท), it means the luminance
of an equivalent achromatic signal with all three
colour components having that same value.)
where:
๐ฌโฒ (video level) denotes a non-linear colour value {๐นโฒ, ๐ฎโฒ, ๐ฉโฒ} or { ๐ณโฒ, ๐ดโฒ, ๐บโฒ} in PQ space in the range [0:1]
๐ญ๐ซ is the luminance of a displayed linear component {๐น๐ซ, ๐ฎ๐ซ, ๐ฉ๐ซ} or ๐๐ซ or ๐ฐ๐ซ, in cd/mยฒ. 4b
๐ denotes the normalized linear colour value, in the range [0:1] (Y=1 correspond to ๐ญ๐ซ=10000 nits)
๐1 = 2610/16384 = 0.1593017578125
๐2 = 2523/4096 ร 128 = 78.84375
๐1 = 3424/4096 = 0.8359375 = ๐3 โ ๐2 + 1
๐2 = 2413/4096 ร 32 = 18.8515625
๐3 = 2392/4096 ร 32 = 18.6875
Reference PQ EOTF, PQ OETF and PQ OOTF
๐ญ๐ซ
PQ
EOTF
Display
Light
Decoding
๐ฌโฒ
๐น๐ท=EOTF[๐ธโฒ
]=10000 Y
๐ =
max แ
๐ธ
1
๐2 โ ๐1 , 0
๐2 โ ๐3
แ
๐ธ
1
๐2
1
๐1
58
59. Parameter Values
Input signal to PQ opto-electronic
transfer function (OETF)
๐ฌ: Scene linear light.
The OETF maps relative scene linear light into the non-linear PQ signal value.
Reference PQ OETF
Use of this OETF will yield the reference
OOTF when displayed on a reference
monitor employing the reference EOTF.
Where
๐ฌโฒ is the resulting non-linear signal (๐นโฒ, ๐ฎโฒ, ๐ฉโฒ) in the range [0:1]
๐ญ๐ซ and ๐ฌ are as specified in the opto-optical transfer function
๐1, ๐2, ๐1, ๐2, ๐3 are as specified in the electro-optical transfer function.
Reference PQ EOTF, PQ OETF and PQ OOTF
๐ธโฒ
= OETF[E] = EOTFโ1
[OOTF[E]] = EOTFโ1
[๐น๐ท]
๐ญ๐ซ
PQ
EOTF
Display
Light
Decoding
Mastering Display
๐ฌ ๐ฌโฒ
OOTF
PQ
๐ฌ๐ถ๐ป๐ญโ๐
PQ OETF
Encoding
Scene
Light
๐ธ๐๐๐นโ1
๐น๐ท =
๐1 + ๐2๐๐1
1 + ๐3๐๐1
๐2
๐ = ๐น๐ท/10000
59
60. Parameter Values
Input signal to PQ opto-optical transfer
function (OOTF)
๐ฌ: Scene linear light.
The OOTF maps relative scene linear light to display linear light.
Reference PQ OOTF
(Note 4c โ The mapping of the camera
sensor signal output to ๐ธ may be
chosen to achieve the desired
brightness of the scene.)
where:
๐ฌ = {๐น๐, ๐ฎ๐, ๐ฉ๐, ๐๐, or ๐ฐ๐} is the signal determined by scene light and scaled by camera exposure
The values ๐ฌ = {๐น๐, ๐ฎ๐, ๐ฉ๐, ๐๐, or ๐ฐ๐} are in the range [0:1] 4c
๐ญ๐ซ is the luminance of a displayed linear component {๐น๐ซ, ๐ฎ๐ซ, ๐ฉ๐ซ} or ๐๐ซ or ๐ฐ๐ซ, in cd/mยฒ.
๐ฌโฒ is a non-linear representation of ๐ฌ
Reference PQ EOTF, PQ OETF and PQ OOTF
FD = G1886[E'] = 100 Eโฒ 2.4
FD = OOTF[E] = G1886 [G709[E]]
FD = G1886 [G709[E]] = G1886 Eโฒ
๐ธโฒ
= ๐บ709 ๐ธ = แ1.099(59.5208๐ธ)0.45 โ 0.099 0.0003024 < ๐ธ < 1
267.84๐ธ 0 < ๐ธ < 0.0003024
FD = OOTF[E] = G1886 [G709[E]] =G1886 [Eโฒ] = 100๐ธโฒ2.4
E:
OOTF[E] = G1886 [G709[E]]
๐ญ๐ซ
PQ
EOTF
Display
Light
Decoding
Mastering Display
๐ฌ ๐ฌโฒ
OOTF
PQ
๐ฌ๐ถ๐ป๐ญโ๐
PQ OETF
Encoding
Scene
Light
60
61. 4 129 254 379 504 629 754 879 1019
1000
900
800
700
600
500
400
300
200
100
0
SMPTE ST 2084
๐๐/๐ฆ๐
PQ 1K EOTF
10 Bit Code Value
4 129 254 379 504 629 754 879 1019
4000
3600
3200
2800
2400
2000
1600
1200
800
400
0
SMPTE ST 2084
๐๐/๐ฆ๐
PQ 4K EOTF
10 Bit Code Value
Display-referred
Image Data
Display Peak Luminance= 1000 nits Display Peak Luminance= 4000 nits
โ The PQ curveโs maximum brightness is always mapped to the maximum brightness of the reference display
to ensure the highest fidelity if the reference and consumer display have similar properties.
Display of PQ signals
61
62. Display of PQ signals
โ The content represented by PQ signals:
โข may be limited to the expected capabilities of the displays on which they are intended to be viewed
โข may be unlimited and represent the full level of highlights captured by the camera
โ In practice, monitors may not reach the full extent of the BT.2100 gamut or the 10 000 ๐๐/๐2
limit of the PQ
signal, resulting in the possibility that some encoded colours may not be displayable on some monitors.
โ Monitors that support PQ may or may not include tone-mapping to bring very high brightness signals down to
the capability of that monitor.
โข Some monitors may clip at their peak output capability (e.g. 2000 ๐๐/๐2
).
โข Some monitors may contain tone mapping that provides a soft-clip.
62
63. โ If the consumer display has a much lower maximum brightness than the reference display:
โ then the entire PQ curve cannot be utilized, resulting in greater quantization (loss of brightness resolution),
โฆโฆโฆwhich can lead to visible contouring artifacts in bright areas.
โ For example,10-bit content mastered on a 10000-nit display would use all 1023 values for the brightness level.
โ Currently most content is mastered on 4000-nit displays, which minimizes this problem.
Display of PQ signals
Display Peak Luminance= 1000 nits
Only 769 values can be viewed, i.e. up to 1000 nits.
Code word 768 is correspond to 1000
nits in 10 bit for PQ10K EOTF
63
64. In
display,
the
code
words
equate
to
specific
screen
Luminance
Code
words
are
equally
spaced
in
perceived
brightness
over
Luminance
0.005
to
10000
nits.
โข The entire PQ curve cannot be utilized
โข Only 769 values can be viewed on 1000
nit consumer display.
โข Loss of brightness resolution
โข Resulting in greater quantization (769
quantized levels is used for 1000 nits in
comparison of a 1000 nits mastered PQ
signal with1024 quantized levels for)
โข It can lead to visible contouring artifacts
in bright areas.
10-bit content mastered on a
10000-nit display 10-bit content on a 1000-nit
consumer display
Code Value 1023
Code Value 0
Code Value 768 (1000 nits)
Code Value 0
Display of PQ signals Code word 768 is correspond to
1000 nits in 10 bit for PQ10K EOTF
64
65. Code words are equally spaced in perceived brightness over this range of luminance.
Equally
Spaced
Code
Words
(10
bits)
Perceived Brightness
๐ญ๐ซ: Display Luminance
Display of PQ signals
65
66. Display of PQ signals
โ For Production Use:
โข Monitors should generally perform a hard clip to the display capabilities
โข Monitors should provide a means to identify pixels that are outside the displayโs capability (either in
brightness or colour)
โ Care should be taken for any content that is allowed to go outside the reference monitor colour gamut or
dynamic range as that would not have been accurately presented to the operator and cannot be trusted as
part of the approved or intended appearance.
โ Reference monitors could provide a selectable overall brightness-attenuation in order to temporarily bring
high brightness signals down to be within the display capability in order to provide a check on any content
encoded brighter than the capability of the reference display.
If a soft-clip is desired, a Look-up-table (LUT) can be
applied to the signal to provide any desired tone mapping.
Display Peak Luminance
500 nits
Display Peak Luminance
10000 nits
Content encoded
brighter than the
capability of the
reference display.
66
67. 1D LUT
โ For each input value, there is one and one only output value; interesting but less than useful for video, where
we are almost always dealing with at least three values for Red, Green and Blue.
โ 1D LUTs have a 1:1 correspondence between the bit-depth and the number of entries.
โ A basic type of LUT for video is three 1D LUTs, one for each color channel.
โ 1D LUTs are useful for adjusting contrast and gamma per color channel.
โ There is no interaction between color channels.
โ As an example a 3X (three channels) 1D LUT could be like this:
R, G, B
3, 0, 0
5, 2, 1
9, 9, 9
โ LUTs consist of long lists of these sets of numbers. This means that:
โข For input R=G=B=0, the output is R=3, G=0, B=0.
โข For input R=G=B=1, the output is R=5, G=2, B=1.
โข For input R=G=B=3, the output is R=9, G=9, B=9.
โข A 1D LUT has separate tables for each color
channel, however for imaging purpose, it is
almost always three 1D LUTs; one for each color
channel.
โข The values of 0 to 255 are the digital color values.
R=G=B=1
R=G=B=0
R=G=B=3
โ
โ
โ
67
68. 3D LUT
โ A 3D LUT is more complex but also allows for more control of the image.
โ 3D LUTs are useful for converting from one color space to another.
โข 3D LUTs use a more sophisticated method of mapping color values from different color spaces.
โ It applies a transformation to each value of a color cube in RGB space.
โ A 3D LUT provides a way to represent arbitrary color space transformations, as opposed to the 1D LUT where a
value of the output color is determined only from the corresponding value of the input color.
The color cube of an unaffected image.
The same image with a LUT applied.
The cube diagram shows how the
colors are shifted by the LUT.
A 3D LUT is a cube or lattice. The values
of 0 to 255 are the digital color values.
68
69. 3D LUT
โ A 3D LUT allows for cross-talk between color channels:
โข A component of the output color is computed from all components of the input color providing the 3D
LUT tool with more power and flexibility than the 1D LUT tool.
โ Because it would be impossibly large to include every single value for each channel, the number of nodes is
limited.
โข With ๐๐ coordinates per axis (a typical size) there are ๐๐ ร ๐๐ ร ๐๐ = ๐, ๐๐๐ nodes total.
โข With ๐๐๐ coordinates per axis there are ๐๐๐ ร ๐๐๐ ร ๐๐๐ = ๐๐, ๐๐๐, ๐๐๐ nodes total.
โ For this reason, only nodes are precisely calculated; between nodes, the value is interpolated, meaning it is
less precise.
R
G
B
โ Rโ
R
G
B
โ Gโ
R
G
B
โ Bโ
69
70. 3D LUT
โ While 1D LUTs are useful for adjusting contrast and gamma per color channel, 3D LUTs are usually more
flexible.
โ 3D LUTs can
โข cross-convert colors between channels
โข alter saturation
โข independently control saturation, brightness, and contrast
โ 3D LUTS must be interpolated from a subset or the LUT could be over a gigabyte in size.
โ 3D LUTs can be integer values or floating point.
โข ๐ ร ๐ ร ๐ = ๐๐๐ nodes โ too small for most transforms
โข ๐๐ ร ๐๐ ร ๐๐ = ๐๐๐๐ nodes โ a reasonable size for preview
โข ๐๐ ร ๐๐ ร ๐๐ = ๐๐๐๐๐๐ nodes โ a rendering quality
70
71. Display of PQ signals
โ If the BT.2100 PQ signal is presented to a monitor that expects a Recommendation ITU-R BT.709 (BT.709) input:
โข Image will appear dim and washed out
โข Colours will be desaturated
โข There will be some hue shifts
PQ HDR Signal
SDR BT.709 Display
HDR Monitor (4K, PQ) SDR Monitor (HD, PQ)
71
72. Display of PQ signals
โ An external 3D LUT can provide the down-mapping function necessary to bring both colour and brightness
into the BT.709 colour volume, thus allowing satisfactory display on the legacy BT.709 monitor.
โ Some monitors may provide this function by means of an internally provided 3D LUT.
โข While this allows viewing on the BT.709 monitor, the resulting images should not be used to make critical
judgements of the HDR production.
โ If PQ signals must be monitored in an environment brighter than the reference environment (5 ๐๐/๐2
surround), manufacturers may provide modified brightness and display characteristics intended to
compensate for the different viewing environment.
PQ HDR Signal
SDR BT.709 Display
HDR Monitor (4K, PQ) SDR Monitor (HD, PQ)
3D LUT
72
73. SMPTE
2084
PQ
Look
Up
Tables
Linear Ramp Test Signal BT.709
Look Up Table SMPTE 2084 1000nits
Reference White 100nits
Look Up Table SMPTE 2084 1000nits
Reference White 300nits
73
Using Look Up Tables (LUTs) In Post Production
2084 HDR (PQ) 0% 2 % 18% 90%
100
%
BT.709 100nits 0 9 41 95 100
HDR 1000nits 0 37 58 75 76
Camera-Side Conversion BT.709 (SDR) to PQ1K
74. 600 cd/mยฒ โshadingโ
e.g. OB truck
1000 cd/mยฒ โshadingโ
e.g. studio gallery
e.g. Code Values 81 - 674
e.g. Code Values 81 - 723
2000 cd/mยฒ โgradeโ
e.g. Code Values 74 - 789
Display
Re-mapping
e.g. Code Values 74 โ636
e.g. Code Values 81 -728
e.g. Code Values 119 - 789
e.g. Code Values 158 -940
โข The signal varies with mastering display.
โข Display re-mapping often required.
PQ Represents Absolute Brightness
Display
Re-mapping
Display
Re-mapping
Display
Re-mapping
e.g. 400 cd/mยฒ, home theatre
e.g. 1000 cd/mยฒ, evening viewing
e.g. 2000 cd/mยฒ, daytime viewing
e.g. 4000 cd/mยฒ, signage display
74
75. 75
Difference between PQ-BT2100 and PQ-ST2084
โ Dolby's perceptual quantizer (PQ) has been standardized as SMPTE ST-2084 as EOTF and OETF.
โ In this standardization the OETF is considered to be the exact inverse of the EOTF, resulting in a linear
OOTF, i.e. no reference OOTF is applied.
โ In addition, PQ is based on an SMPTE and Dolby subject study to determine audience preference over
the required dynamic range. Since the study showed that viewers prefer a luminance range between
0.001 cd/mยฒ and 10,000 cd/mยฒ, the standard covers exactly this dynamic range.
76. 76
Difference between PQ-BT2100 and PQ-ST2084
โ ITU-R BT.2100, specifies PQ as a 10-bit EOTF and OETF, but in combination with a reference OOTF.
โ The OOTF being considered in the camera (or being imposed in the production process), makes PQ a
display-related system that is initially designed to provide an intended image impression in a BT.2100
defined reference environment (5 nits or cd/mยฒ around the monitor while avoiding scattered light on the
display). If this reference condition is not fulfilled, the viewer will get a wrong impression of the image.
โ Therefore, PQ as an absolute brightness metric basically ensures that an image is reproduced on all
systems with the same absolute luminance, which ensures good comparability.
79. Human Eye Sensitivity and Dynamic Range
Highlights
โข The human eye is less sensitive to changes in brightness for
bright areas of a scene.
โข Not so much dynamic range is required for these areas and
they can be compressed without reducing display quality.
Mid-tones
โข The human eye is reasonably sensitive to
changes in mid-tone brightness.
Low-lights
โข The human eye is more sensitive to changes in
brightness in darker areas of a scene and plenty of
dynamic range is needed to record these areas well.
Eye
Sensitivity
Scene Brightness
Less
Dynamic
Range
More
Dynamic
Range
โ๐ฐ
๐ฐ
= ๐ช๐๐๐๐๐๐๐ (โ ๐. ๐๐)
79
80. Human Eye Sensitivity and Dynamic Range
Eye
Sensitivity
Scene Brightness
Less
Dynamic
Range
More
Dynamic
Range
โข For much brighter specular highlights, do not need as
many code words to represent them (large L).
โข In the darker areas of a picture (small L), minor changes
can be seen much more than in brighter areas of a
picture (small โL is detectable). So more code words
should be given to the darker areas.
โข The eye needs more dynamic range in low light
levels than in high light levels
โข More Code Words or More Bits
Minimum Detectable Contrast (%) =
๐๐ข๐ง๐ข๐ฆ๐ฎ๐ฆ ๐๐๐ญ๐๐๐ญ๐๐๐ฅ๐ ๐๐ข๐๐๐๐ซ๐๐ง๐๐ ๐ข๐ง ๐๐ฎ๐ฆ๐ข๐ง๐๐ง๐๐
๐๐๐๐ค๐ ๐ซ๐จ๐ฎ๐ง๐ ๐๐ฎ๐ฆ๐ข๐ง๐ฎ๐ง๐๐ ๐๐๐ฏ๐๐ฅ
ร ๐๐๐
For a constant number of bits (ex, 10 bits codes), we need to give more code words to the lower light levels than bright areas to improve how we see the blacks.
=
โ๐ณ
๐ณ
ร100
80
81. Human Eye Sensitivity and Dynamic Range
โ Linear sampling wastes codes
values where they do little good.
โ Log encoding distributes codes
values more evenly โ in a way
that more closely conforms to
how human perception works.
Eye
Sensitivity
Scene Luminance
Eye
Sensitivity
Scene Luminance
Steep perceptual slope means
high gain to blacks
Eye
Sensitivity
Scene Brightness
Perceptual
Quantizer (PQ)
Perception is 1/3 power-law
โcube-rootโ
81
82. Contouring
(Banding)
BT. 1886 Performance in 10-Bit, 15-Bit and 13-Bit Log
Optical
Electronic
OETF
(Camera Gamma)
How many bits is required for
avoiding banding effect? Gamma: Wasted bits in bright regions
Log: Wasted bits in dark regions
Above Threshold
โข Step edges are visible
โข Visible contouring/banding
Below Threshold
โข Step edges are invisible
โข Smooth gradients
Visible Difference between shades resulting in banding
Smooth gradient with no discernable difference between shades
Minimum
Contrast
Step
(%)
Luminance in nits (๐/๐๐)
โ๐ณ
๐ณ
ร
100
82
83. Visible Difference between shades resulting in banding
Smooth gradient with no discernable difference between shades
Optical
Electronic
OETF
(Camera Gamma)
How many bits is required for
avoiding banding effect?
PQ EOTF on Barten Ramp
Gamma: Wasted bits in bright regions
Log: Wasted bits in dark regions
Above Threshold
โข Step edges are visible
โข Visible contouring/banding
Below Threshold
โข Step edges are invisible
โข Smooth gradients
Contouring
(Banding)
Luminance in nits (๐/๐๐)
Minimum
Contrast
Step
(%)
โ๐ณ
๐ณ
ร
100
83
84. Contrast Sensitivity
โ This graph is redrawn from Schreiberโs Fundamentals of Electronic Imaging Systems.
At very low luminance values, the curve departs from logarithmic
behaviour and approximates a square-root; this characteristic is
called the de Vries-Rose law (Hessel de Vries, Albert Rose).
The flat portion of the curve shows that the
perceptual response to luminance โ termed
lightness โ is approximately logarithmic.
โ๐ณ
๐ณ
= ๐ช โ ๐. ๐๐
Slope=0.5
The transition occurs between absolute
luminance values of 0.1 to 1 nt.
(0.025)
(0.0158)
(0.039)
(0.063)
(0.1)
(0.158)
(
โ๐ณ
๐ณ
)
Quantization Effects (Banding): The Schreiber Threshold
โ๐ณ
๐ณ
= ๐ฒ
Over a range of luminance values of about
300:1, the discrimination threshold of vision is
approximately a constant ratio of luminance. ๐บ =
๐
๐ช๐๐๐
๐ช๐๐๐ =
โ๐ณ๐๐๐
๐ณ
84
85. HLG OETF Facts
1
0.8
0.6
0.4
0.2
0
Video Signal
Relative Sensor Output
0 0.5 1 1.5 2 2.5 3
ConventionalSDR CameraCurve
In the low lights it becomes increasingly difficult to perceive banding. That is, the
threshold of visibility for banding becomes higher as the image gets darker. It
means for small values of ๐ณ, with decreasing the ๐ณ, โ๐ณ is increased.
โข So an ideal OETF would be a gamma law in the low lights because it has
invisible quantization distortion because of higher threshold for visibility of
banding or contouring.
De Vries-Rose law
๐ณ โ โ๐ณ ๐๐ ๐๐๐๐ ๐๐๐๐๐๐๐๐๐๐ ๐๐ ๐ณ
โ
De Vries-Rose Law
Critical Contrast โ๐ณ = ๐ฒ ๐ณ
85
86. HLG OETF Facts
1
0.8
0.6
0.4
0.2
0
Video Signal
Relative Sensor Output
0 0.5 1 1.5 2 2.5 3
Camera LogCurve
In the brighter parts and highlights of an image the threshold for
perceiving quantization error (banding or contouring) is approximately
constant, so quantization distortion visibility is constant.
โข This implies a logarithmic OETF would provide the maximum
dynamic range for a given bit depth.
Weberโs law
WeberโFechner Law
Critical Contrast โ๐ณ = ๐ช๐ณ โ ๐. ๐๐๐ณ
โ๐ณ ๐๐ ๐ ๐๐๐๐๐๐๐๐ ๐๐๐๐๐๐๐๐๐๐ ๐๐ ๐ณ
86
88. 1
0.8
0.6
0.4
0.2
0
Video Signal
Relative Sensor Output
0 0.5 1 1.5 2 2.5 3
HLG HDR Camera Curve
Ideal OETF
An ideal OETF might be logarithmic in the high tones and a gamma law in
the low lights, which is essentially the form of the hybrid log-gamma OETF.
HLG OETF Facts
88
89. Conventional SDR CameraCurve
Video
Signal
Relative Sensor Output
Camera Log Curve
Video
Signal
Relative Sensor Output
Best of both should be selected.
Video
Signal
Relative Sensor Output
Hybrid Log Gamma HDR Camera Curve
Video
Signal Relative Sensor Output
HLG OETF Facts
In the low lights it becomes increasingly difficult to perceive
banding. That is, the threshold of visibility for banding
becomes higher as the image gets darker.
โข So an ideal OETF would be a gamma law in the low
lights because it has invisible quantization distortion
because of higher threshold for visibility of banding
or contouring.
In the brighter parts and highlights of an image the
threshold for perceiving quantization error (banding or
contouring) is approximately constant, so quantization
distortion visibility is constant.
โข This implies a logarithmic OETF would provide
the maximum dynamic range for a given bit
depth.
Weberโs law
De Vries-Rose law
0 0.5 1 1.2 2 2.5 3 0 0.5 1 1.2 2 2.5 3
0 0.5 1 1.2 2 2.5 3
0 0.5 1 1.2 2 2.5 3
1
0.8
0.6
0.4
0.2
0
1
0.8
0.6
0.4
0.2
0
1
0.8
0.6
0.4
0.2
0
1
0.8
0.6
0.4
0.2
0
An ideal OETF might be logarithmic in the high tones
and a gamma law in the low lights, which is essentially
the form of the hybrid log-gamma OETF.
Ideal OETF
89
90. HLG OETF Facts
Knee
โ The knee characteristic compresses the image highlights to prevent the signal from clipping or being โblown outโ
(overexposed) and so extend the dynamic range of the signal
Weberโs law
โ In the brighter parts and highlights of an image the threshold for perceiving quantization error (banding or contouring)
is approximately constant, so quantization distortion visibility is constant.
โข This implies a logarithmic OETF would provide the maximum dynamic range for a given bit depth.
De Vries-Rose law
โ Proprietary logarithmic OETFs are in widespread use. But in the low lights it becomes increasingly difficult to perceive
banding. That is, the threshold of visibility for banding becomes higher as the image gets darker.
โ The conventional gamma OETF used for SDR comes close to matching the De Vries-Rose law, which is perhaps not
coincidental since gamma curves were designed for dim CRT displays.
โข So an ideal OETF would be a gamma law in the low lights because it has invisible quantization distortion because
of higher threshold for visibility of banding or contouring.
.
So an ideal OETF might be logarithmic in the high tones and a gamma law in the low
lights, which is essentially the form of the hybrid log-gamma OETF. 90
91. Hybrid Log-Gamma (HLG) HDR-TV OETF
Standardized as ARIB STB-B67 and ITU-R BT.2100
a = 0.17883277
b = 0.28466892
c = 0.55991073
๐ฌโฒ
= ๐ถ๐ฌ๐ป๐ญ ๐ฌ =
๐๐ฌ ๐ โค ๐ฌ โค
๐
๐๐
๐. ๐๐ ๐๐๐ฌ โ ๐ + ๐
๐
๐๐
< ๐ฌ โค ๐
a = 0.17883277, b = 0.28466892, c = 0.55991073
Linear Scene Light
Signal
Level
SDR OETF
SDR with Knee
HDR HLG OETF
Knee point: 87.5% signal level
Reflectance Object or Reference
(Luminance Factor, %)
Nominal Signal
Level (%)
Grey Card (18% Reflectance) 42.5
Reference or Diffuse White (100%
Reflectance)
79
A notional SDR โkneeโ is shown on the same plot, with
a breakpoint of 87.5% signal level, which extends the
SDR dynamic capture range substantially.
SDR OETF
SDR with Knee
HDR HLG OETF
E (Scene Light) : signal for each colour component {Rs, Gs, Bs} proportional to scene linear light and scaled by
camera exposure, normalized to the range [0:1]
Eโฒ (Video Level): The resulting non-linear signal {Rโฒ, Gโฒ, Bโฒ} in the range [0:1].
ITU-R Application 2 ,ARIB B67 (Association of Radio Industries and Businesses)
HLG can capture
nearly a factor of 3
more luminance than
100% reflectivity.
91
92. Hybrid Log-Gamma (HLG) HDR-TV OETF
Standardized as ARIB STB-B67 and ITU-R BT.2100
a = 0.17883277
b = 0.28466892
c = 0.55991073
๐ฌโฒ
= ๐ถ๐ฌ๐ป๐ญ ๐ฌ =
๐๐ฌ ๐ โค ๐ฌ โค
๐
๐๐
๐. ๐๐ ๐๐๐ฌ โ ๐ + ๐
๐
๐๐
< ๐ฌ โค ๐
E (Scene Light) : signal for each colour component {Rs, Gs, Bs} proportional to scene linear light and scaled by
camera exposure, normalized to the range [0:1]
Eโฒ (Video Level): The resulting non-linear signal {Rโฒ, Gโฒ, Bโฒ} in the range [0:1].
a = 0.17883277, b = 0.28466892, c = 0.55991073
Linear Scene Light
Signal
Level
SDR OETF
SDR with Knee
HDR HLG OETF
Knee point: 87.5% signal level
More
Code
Words
for
Dark
Area
Less
Code
Words
for
Bright
Area
A notional SDR โkneeโ is shown on the same plot, with
a breakpoint of 87.5% signal level, which extends the
SDR dynamic capture range substantially.
Reflectance Object or Reference
(Luminance Factor, %)
Nominal Signal
Level (%)
Grey Card (18% Reflectance) 42.5
Reference or Diffuse White (100%
Reflectance)
79
SDR OETF
SDR with Knee
HDR HLG OETF
ITU-R Application 2 ,ARIB B67 (Association of Radio Industries and Businesses)
HLG can capture
nearly a factor of 3
more luminance than
100% reflectivity.
92
93. Code Levels Distribution in HDR
Uniform (equally spaced) Code Words for Perceived Brightness
Perceived Brightness
93
94. Code Levels Distribution in HDR
Uniform (equally spaced) Code Words for Perceived Brightness
More Code Words
for Dark Area
Less Code Words for
Bright Area
Perceived Brightness
94
95. Code Words Utilization by Luminance Range, Gamma 2.4
Too many code words allocated
to very bright regions and not
enough allocated to dark regions.
95
96. โ These plots assume that two cameras, one Recommendation ITU-R BT.2020 and the other BT.2100 (that is,
one SDR and one HDR), are set up with the same sensitivity.
โ The 18% grey may be useful when trying to match SDR and HDR cameras as the 18% grey should not be
affected by any SDR camera โkneeโ.
โข E.g. if both cameras were looking at the same 18% grey chart, then their sensitivities (gain, iris, and shutter
time) could be adjusted so that the signal level was 42.5% of nominal full signal level for both cameras.
โข Setting 18% grey to 42.5% results in the diffuse white signal level being 100% for SDR, and 79% for HLG.
Hybrid Log-Gamma (HLG) HDR-TV OETF
SDR ITU-R BT.2020
HDR ITU-R BT.2100
18% Grey Chart
Nominal Full Signal Level
42.5%
Nominal Full Signal Level
42.5%
100%
79%
100% Grey Chart
96
97. โ Above 50% signal level the HDR OETF is logarithmic, which means it can capture higher light levels (such
as specular reflections and highlights) without clipping.
โ When the two camerasโ (SDR and HDR) sensitivities are equalized:
โข For signal levels at.or below 50% both the SDR (BT.2020) and HDR responses to light amplitude would
be almost the same.
Hybrid Log-Gamma (HLG) HDR-TV OETF
Reflectance Object or
Reference
(Luminance Factor, %)
Nominal
Signal Level
(SDR%)
Nominal
Signal Level
(HLG%)
Grey Card (18%
Reflectance)
42.5 42.5
Reference or Diffuse White
(100% Reflectance)
100 79
SDR OETF
SDR with Knee
HDR HLG OETF
97
98. Hybrid Log-Gamma (HLG) HDR-TV OETF
๐ = ๐. ๐๐๐๐ณ๐.๐๐
โ ๐. ๐๐๐ 0.018 < L <1
๐ = ๐. ๐๐๐๐ณ 0 < L < 0.018
๐ฌโฒ
= ๐ถ๐ฌ๐ป๐ญ ๐ฌ =
๐๐ฌ ๐ โค ๐ฌ โค
๐
๐๐
๐. ๐๐ ๐๐๐ฌ โ ๐ + ๐
๐
๐๐
< ๐ฌ โค ๐
HLG OETF
0.2
0.18
0.16
0.14
0.12
0.1
0.08
0.06
0.04
0.02
0
0 0.01 0.05
Video
Signal
0.02 0.03 0.04
Relative Sensor Output
HLG
BT.709
SDR OETF
โ There are small differences between the two plots below 50% of nominal signal range.
โ This is because SDR OETFs include a linear portion near black (๐ = ๐. ๐๐๐๐ณ) to avoid excessive noise
amplification. HLG, by contrast, uses a pure square root OETF at low levels ( ๐๐ฌ).
โข This allows HLG to achieve higher dynamic range โin the blacksโ, but it does mean that camera
manufacturers must use an alternative to the linear part of the SDR OETF to avoid excessive noise
amplification in the black.
98
99. Preferred Min.
Preferred Max.
(Narrow Range)
(White)
(Black)
(super-whites)
(sub-blacks)
System
Bit Depth
Range in Digital sample (Code) Values
Nominal
Video Range
Preferred
Min./Max.
Total Video
Signal Range
8-bit 16-235 5-246 1-254
10-bit 64-940 20-984 4-1019
12-bit 256-3760 80-3936 16-4079
16-bit 4096-60160 1280-62976 256-65279
Extended
Range
EBU R103: Video Signal Tolerance in Digital Television Systems
โ Television and broadcasting
do not primarily use the โfull
rangeโ of digital sample
(code) values available in a
given format.
โ Another term, โextended
rangeโ is not formally defined
but is sometimes used for the
range 64 โ 1019 (10-bit), so
including super-whites, whilst
maintaining sub-blacks.
โ SDI always reserves some
code values for its own signal
processing requirements.
99
This percentage are used just in narrow range.
100. Preferred Min.
Preferred Max.
(Narrow Range)
(White)
(Black)
(super-whites)
(sub-blacks)
System
Bit Depth
Range in Digital sample (Code) Values
Nominal
Video Range
Preferred
Min./Max.
Total Video
Signal Range
8-bit 16-235 5-246 1-254
10-bit 64-940 20-984 4-1019
12-bit 256-3760 80-3936 16-4079
16-bit 4096-60160 1280-62976 256-65279
Extended
Range
EBU R103: Video Signal Tolerance in Digital Television Systems
โ Often โNarrow Rangeโ or
โVideo Rangeโ is used in
television and
broadcasting.
โ Narrow range signals
โข may extend below black
(sub-blacks)
โข may exceed the nominal
peak values (super-
whites)
โข should not exceed the
video data range.
100
This percentage are used just in narrow range.
101. Video Signal
โ In a video signal, each primary component should lie between 0 and 100% of the Narrow Range (Video Range) between
black level and the nominal peak level (R and G and B).
Video Signal Tolerance
โ The EBU recommends that, the RGB components and the corresponding Luminance (Y) signal should not normally exceed
the โPreferred Minimum/Maximumโ range of digital sample levels.
โ Any signals outside the โPreferred Minimum/Maximumโ range are described as having a gamut error or as being โOut-of-
Gamutโ.
โ Signals shall not exceed the โTotal Video Signal Rangeโ, overshoots that attempt to โexceedโ these values may clip.
System Bit Depth Range in Digital sample (Code) Values
Nominal Video Range Preferred Min./Max. Total Video Signal Range
8-bit 16-235 5-246 1-254
10-bit 64-940 20-984 4-1019
12-bit 256-3760 80-3936 16-4079
16-bit 4096-60160 1280-62976 256-65279
EBU R103: Video Signal Tolerance in Digital Television Systems
101
102. โ Note that the conventional โnarrow rangeโ digital signal can actually support signal levels of up to 109% of
nominal full scale.
โข This is to accommodate overshoots and highlights.
โ If this additional signal range is used (though not all equipment supports it) then even higher light levels
may be captured without clipping.
Hybrid Log-Gamma (HLG) HDR-TV OETF
Preferred Max.
(Narrow Range)
(White)
(super-whites)
102
103. โ Considering a nominal full scale signal (i.e. 100% signal level), and with the cameras set up as mentioned
(When the two camerasโ (SDR and HDR) sensitivities are equalized):
โ If the signal is not allowed to excurse to the maximum 100% signal range then:
โ The SDR camera can capture objects no brighter than 100% reflective (i.e. no highlights).
โ The HLG camera increases the luminance that can be captured by a factor of 3.
Hybrid Log-Gamma (HLG) HDR-TV OETF
SDR ITU-R BT.2020
HDR ITU-R BT.2100
Nominal Full Signal Level
42.5%
Nominal Full Signal Level
42.5%
100%
100%
Luminance Equivalent to 300% Reflectivity
(โ3 times more than diffuse whiteโ )
18% Grey Chart
Luminance Equivalent to 100% Reflectivity
(โdiffuse whiteโ )
103
104. โ Considering a nominal full scale signal (i.e. 100% signal level), and with the cameras set up as mentioned
(When the two camerasโ (SDR and HDR) sensitivities are equalized):
โ If the signal is allowed to excurse to the maximum 109% range (super-whites) then:
โ SDR can capture luminance equivalent to 120% reflectivity
โ HLG can capture nearly a factor of 5 more luminance than 100% reflectivity
Hybrid Log-Gamma (HLG) HDR-TV OETF
SDR ITU-R BT.2020
HDR ITU-R BT.2100
Nominal Full Signal Level
42.5%
Nominal Full Signal Level
42.5%
100%
100%
Luminance Equivalent to 120% Reflectivity
(โ1.2 times more than diffuse whiteโ )
Luminance Equivalent to 500% Reflectivity
(โ5 times more than diffuse whiteโ )
18% Grey Chart
104
105. โ A native interpretation of these plots might suggest that the dynamic range of HLG is only 3 times greater
than SDR, but this is not the case because:
I. HDR is about more than just increasing the brightness of highlights.
๏ Creating the detail in โlowlightsโ and โin the blackโ is also very important and HLG adds much
dynamic range here.
II. The OETF describes the capture dynamic range. The dynamic range on the display is greater
because of overall system gamma.
๏ The OOTF maps relative scene linear light to display linear light.
๏ With a typical system gamma of 1.2, and the camera sensitivity adjusted as described, HLG
supports display highlights which are a factor of 3.7 (or 6.9 with super-whites) higher than diffuse
white.
Hybrid Log-Gamma (HLG) HDR-TV OETF
31.2
= 3.7
51.2
= 6.9
๐ฌ๐๐
OOTF
๐ฌ๐๐๐
๐ฌ๐๐๐ = ๐ฌ๐๐
๐พ๐๐๐๐๐๐
105
106. โ The foregoing discussion assumes that โdiffuse whiteโ produces 100% signal output for SDR cameras.
โ Whilst this may be true for some programmes, the signal level for diffuse white is not defined for SDR signals.
โข In practice diffuse white varies between about 90% and 115% depending on genre, geographical
region, and artistic preference.
โข Drama, in particular, tends to set diffuse white at a lower signal level.
๏ This supports more artistically pleasing pictures that can contain some highlight detail.
โ HLG supports a much greater dynamic range than SDR, and can take advantage of this by setting diffuse
white at a lower signal level to support more highlight dynamic range.
Hybrid Log-Gamma (HLG) HDR-TV OETF
106
107. Report ITU-R BT.2408:
โ For HLG HDR, diffuse white should be
set at a signal level of 75%.
โ It configured by making the output
from an 18% grey card correspond to
a signal level of 38%, rather than the
42.5%.
โ Setting 18% grey to 38% results in the
diffuse white signal level being 89% for
SDR, and 75% for HLG.
Hybrid Log-Gamma (HLG) HDR-TV OETF
Reflectance Object or Reference
(Luminance Factor, %)
Nominal Signal Level
(HLG %)
Grey Card (18% Reflectance) 38
Reference or Diffuse White (100% Reflectance) 75
18% grey card correspond to a signal level of
38% and diffuse white at a signal level of 75%.
18% grey card correspond to a signal level of
42.5%, diffuse white at a signal level of 79%.
Report ITU-R BT.2408
Report ITU-R BT.2408
With slightly lower signal level for diffuse white, the
dynamic range available for highlights is increased.
SDR ITU-R BT.2020
HDR ITU-R BT.2100
18% Grey Chart
Nominal Full Signal Level
38%
Nominal Full Signal Level
38%
89%
75%
100% Grey Chart
107
108. Hybrid Log-Gamma (HLG) HDR-TV OETF
Report ITU-R BT.2408:
โ If the signal is not allowed to excurse to the maximum 100% signal range then SDR can now support scene
luminance equivalent to 125% of diffuse white, and HDR can support scene luminance of 375% diffuse
white.
Report ITU-R BT.2408
SDR ITU-R BT.2020
HDR ITU-R BT.2100
Nominal Full Signal Level
38%
Nominal Full Signal Level
38%
100%
100%
Luminance Equivalent to 125% Reflectivity
(โ1.25 times more than diffuse whiteโ )
Luminance Equivalent to 375% Reflectivity
(โ3.75 times more than diffuse whiteโ )
18% Grey Chart
108
109. Hybrid Log-Gamma (HLG) HDR-TV OETF
Report ITU-R BT.2408:
โ These figures increase to 150% and about 620% if super-whites (109% signal range) are used.
โข So the use of super-whites is much more advantageous for HLG than it is for SDR.
Report ITU-R BT.2408
SDR ITU-R BT.2020
HDR ITU-R BT.2100
Nominal Full Signal Level
38%
Nominal Full Signal Level
38%
100%
100%
Luminance Equivalent to 150% Reflectivity
(โ1. 5 times more than diffuse whiteโ )
Luminance Equivalent to 620% Reflectivity
(โ6.2 times more than diffuse whiteโ )
18% Grey Chart
Preferred Max.
(Narrow Range)
(White)
(super-whites)
109
110. Hybrid Log-Gamma (HLG) HDR-TV OETF
Report ITU-R BT.2408:
โ Note that these figures increase further to 163% and 890% at the display when a typical system gamma of
1.2 is used.
1.51.2
= 1.63
6.21.2
= 8.9
Report ITU-R BT.2408
SDR ITU-R BT.2020
HDR ITU-R BT.2100
Nominal Full Signal Level
38%
Nominal Full Signal Level
38%
100%
100%
Luminance Equivalent to 150% Reflectivity
(โ1. 5 times more than diffuse whiteโ )
Luminance Equivalent to 620% Reflectivity
(โ6.2 times more than diffuse whiteโ )
๐ฌ๐๐
OOTF
๐ฌ๐๐๐
๐ฌ๐๐๐ = ๐ฌ๐๐
๐พ๐
110
111. Reference Viewing Environment for Critical Viewing of HDR
Parameter Parameter Value
Surround and Periphery 3a Neutral grey at D65
Luminance of Surround 5 nits
Luminance of Periphery โค 5 nits
Ambient Lighting Avoid light falling on the screen
Viewing Distance 3b
For 1920 ร1080 format: 3.2 picture heights
For 3840 ร2160 format: 1.6 to 3.2 picture heights
For 7680 ร4320 format: 0.8 to 3.2 picture heights
Peak Luminance of Display 3c โฅ 1 000 nits
Minimum Luminance of Display (Black Level) 3d โค 0.005 nits
Note 3a โ โSurroundโ is the area surrounding a display that can affect the adaptation of the eye, typically the wall or curtain
behind the display; โPeripheryโ is the remaining environment outside of the surround.
Note 3b โ When picture evaluation involves resolution, the lower value of viewing distance should be used. When resolution
is not being evaluated, any viewing distance in the indicated range may be used.
Note 3c โ This is not to imply this level of luminance must be achieved for full screen white, rather for small area highlights.
Note 3d โ For PQ in a non-reference viewing environment, or for HLG (in any viewing environment), the black level should
be adjusted using the PLUGE test signal and procedure specified in Recommendation ITU-R BT.814.
111
112. โ The overall system non-linearity, or โrendering intentโ is defined by the opto-optical transfer function, or
OOTF.
โ The OOTF maps relative scene linear light to display linear light.
โ Rendering intent is needed to compensate for the psychovisual effects of watching an emissive screen in
a dark or dim environment, which affects the adaptation state (and hence the sensitivity) of the eye.
System Gamma
Normalized RGB
RโGโB
๐ธ๐บ
(To compensate for the psychovisual effects of watching
an emissive screen in a dark or dim environment)
Output Luminance
112
113. System Gamma in Cinema:
โ Traditionally movies were, and often still are, shot on negative film with a gamma of about 0.6.
โ They were then displayed from a print with a gamma of between 2.6 and 3.0.
โ This gives movies a system gamma of between 1.6 (0.6ร2.6) and 1.8 (0.6ร3), which is needed because of
the dark viewing environment.
System Gamma in SDR:
โ The SDR TV has an OOTF which is also a gamma curve with a system gamma of 1.2.
System Gamma
113
114. โ Simply applying a gamma curve to each red, green and blue components separately as is done for SDR
television distorts the colour; in particular it distorts saturation but also to a lesser extent the hue.
โ Example:
โ In this example, the ratio of green to blue and red has increased (from 3:1 to 9:1).
โ This means, a green pixel would have appeared as a discernibly different shade of green.
โ This approach is far from ideal if it is wished to avoid distorting colours when they are displayed.
The Problem of Appling Gamma to R,G and B Components
Normalized RGB
(0.25, 0.75, 0.25)
RโGโB
(0.0625, 0.5625, 0.0625)
(i.e. squaring the value of the components)
Pixel has got slightly darker
๐ธ๐ซ = ๐ Gamma Circuit
Gamma Circuit
Gamma Circuit
114
115. =
OOTF
gamma 1.5
on RGB
Scene Light Display Light
=
30% 90% 95% 78% 16% 85% 93% 71%
โข Each production format looks different due to different OOTFs (Hue, Saturation, Tone)
โข BT.709/sRGB colour simulation
โข OOTF gamma 1.5 to highlight effect
โข Traditional OOTF โgammaโ on RGB increases colour saturation
Increased
colour
saturation
The Problem of Appling Gamma to R,G and B Components
Gamma Circuit
Gamma Circuit
Gamma Circuit
115
116. =
Scene Light Display Light
=
30% 90% 95% 78% 16% 85% 93% 71%
OOTF
gamma 1.5
on RGB
โข BT.709/sRGB colour simulation
โข OOTF gamma 1.5 to highlight effect
โข Traditional OOTF โgammaโ on RGB increases colour saturation
โข Scene and Display Light are Different Colours
Increased
colour
saturation
The Problem of Appling Gamma to R,G and B Components
Gamma Circuit
Gamma Circuit
Gamma Circuit
116
117. =
Scene Light Display Light
=
30% 90% 95% 79% 26% 78% 84% 68%
OOTF
gamma 1.5
on Luminance
in HLG
Resultant
colour
saturation
Appling OOTF to Luminance Component to Avoid Colour Changes
โข HLG Applies Gamma on Luminance to Preserves Colour Saturation of Original Scene
โข Necessary as different peak luminance displays require different gammas
117
118. โ Instead of the current SDR practice of applying a gamma curve independently to each colour
component, for HDR it should be applied to the luminance alone.
โ By applying rendering intent (OOTF) to the luminance component only it is possible to avoid colour
changes in the display.
โ According to Recommendation ITU-R BT.2100, luminance is given by:
โ ๐๐: normalized linear scene luminance
โ ๐น๐, ๐ฎ๐ and ๐ฉ๐: normalized linear scene light (i.e. before applying OETF) colour components signals
๐๐ = ๐. ๐๐๐๐๐น๐ + ๐. ๐๐๐๐๐ฎ๐ + ๐. ๐๐๐๐๐ฉ๐
HLG OETF HLG EOTF
๐ฌ: [๐,๐] ๐ฌโฒ: [๐,๐]
๐ญ๐ซ
Linear Scene-light
Signals ๐น๐, ๐ฎ๐, ๐ฉ๐
Linear Display-light
Signals ๐น๐ซ, ๐ฎ๐ซ, ๐ฉ๐ซ
Non-linear
Signals ๐น๐, ๐ฎ๐, ๐ฉ๐
Appling OOTF to Luminance Component to Avoid Colour Changes
๐ญ๐บ
118
119. โ The HLG reference OOTF is therefore given by:
๐ญ๐ซ: luminance of a displayed linear component {๐น๐ซ, ๐ฎ๐ซ, or ๐ฉ๐ซ}, in cd/mยฒ
๐ฌ: signal for each colour component {๐น๐บ, ๐ฎ๐บ, ๐ฉ๐บ} proportional to scene linear light and scaled by camera
exposure, normalized to the range [0:1].
๐ถ : user adjustment for the luminance of the display, commonly known in the past as a โcontrast controlโ.
โข It represents ๐ณ๐พ, the nominal peak luminance of a display for achromatic pixels in cd/mยฒ.
๐ธ : is an exponent, which varies depending on ๐ณ๐พ, and which is equal to 1.2 at the nominal display peak
luminance of 1000 cd/mยฒ
๐๐ = ๐. ๐๐๐๐๐น๐ + ๐. ๐๐๐๐๐ฎ๐ + ๐. ๐๐๐๐๐ฉ๐
๐ญ๐ซ = ๐ถ๐ถ๐ป๐ญ ๐ฌ = ๐๐๐บ
๐ธโ๐
๐ฌ
๐น๐ซ = ๐๐๐บ
๐ธโ๐
๐น๐บ
๐ฎ๐ซ = ๐๐๐บ
๐ธโ๐
๐ฎ๐บ
๐ฉ๐ซ = ๐๐๐บ
๐ธโ๐
๐ฉ๐บ
Appling OOTF to Luminance Component to Avoid Colour Changes
119
120. Reference OOTF = OETF (HLG) + EOTF (HLG)
โ Opto-Electronic Transfer Function (OETF): Scene light to electrical signal
โ Electro-Optical Transfer Function (EOTF): Electrical signal to scene light
OOTF (Opto-Optical Transfer Function)
HLG OETF HLG EOTF
๐ฌ: [๐, ๐] ๐ฌโฒ
: [๐, ๐]
๐ญ๐ซ
Linear Scene-light
Signals ๐น๐, ๐ฎ๐, ๐ฉ๐
Non-linear
Signals ๐น๐, ๐ฎ๐, ๐ฉ๐
Linear Display-light
Signals ๐น๐ซ, ๐ฎ๐ซ, ๐ฉ๐ซ
๐ญ๐บ
120
121. โ Opto-Electronic Transfer Function (OETF): Scene light to electrical signal
โ Electro-Optical Transfer Function (EOTF): Electrical signal to scene light
OOTF (Opto-Optical Transfer Function)
HLG OETF HLG EOTF
๐ฌ: [๐, ๐] ๐ฌโฒ
: [๐, ๐]
Linear Scene-light
Signals ๐น๐, ๐ฎ๐, ๐ฉ๐
Non-linear
Signals ๐น๐, ๐ฎ๐, ๐ฉ๐
Linear Display-light
Signals ๐น๐ซ, ๐ฎ๐ซ, ๐ฉ๐ซ
Non linear color value,
encoded in PQ space in
the range [0,1].
The signal determined by scene
linear light, scaled by camera
exposure in the range [0:1].
๐ญ๐ซ :The luminance of a displayed linear
component {๐น๐ซ, ๐ฎ๐ซ, ๐ฉ๐ซ} in cd/mยฒ.
The luminance of a single colour component (๐น๐ซ, ๐ฎ๐ซ,
๐ฉ๐ซ ), means the luminance of an equivalent
achromatic signal with all three colour components
having that same value.
๐ญ๐ซ
๐ญ๐บ
121
122. To display HDR accurately, same settings between OETF of camera and EOTF of display are needed!!
--> Different settings make HDR signal and display to look wrong
Cancel
OOTF=Artistic Intent
(seasoning)
OETF-1 OOTF
Input [%]
Output
[cd/ใก ]
Camera Monitor
Display Light
EOTF
Optical Signal
Scene Light
Electronic Signal
OETF
OOTF Position in HLG
Scene-Referred Signal
Linear Scene Light
Output [%]
Input [cd/ใก ]
Display Linear Light
122
123. To display HDR accurately, same settings between OETF of camera and EOTF of display are needed!!
--> Different settings make HDR signal and display to look wrong
Cancel
OOTF=Artistic Intent
(seasoning)
OETF-1 OOTF
Input [%]
Output
[cd/ใก ]
Camera Monitor
Display Light
EOTF
Optical Signal
Scene Light
Electronic Signal
OETF
OOTF Position in HLG
Scene-Referred Signal
Linear Scene Light
Output [%]
Input [cd/ใก ]
Display Linear Light
The HLG system specifies a scene-referred HDR signal which means that every pixel value in the image
represents the light intensity in the captured scene.
โข Therefore, the transfer characteristics can be implemented directly in the camera and the signal
produced by the camera is independent of the display.
โข That means that there is no additional processing and no metadata are required to convert the signal
for a particular screen.
123
124. HLG End to End Chain
๐ฌ
๐ญ๐ซ
Non linear color value, encoded
in HLG space in the range [0,1].
The signal determined
by scene linear light, scaled by
camera exposure in the range [0:1].
The luminance of a displayed
linear component
Scene
Light
Scene-referred
Image Data
HLG OETF
Display
Light
Encoding
Reference Display
HLG
O๐๐๐ โ๐
Decoding
OOTF
HLG EOTF
๐ฌโฒ
๐ฌ = {๐น๐, ๐ฎ๐, ๐ฉ๐}: The signal determined by scene linear light and scaled by camera exposure in the range [0:1].
๐ฌโ= {๐นโฒ, ๐ฎโฒ, ๐ฉโฒ}: A non-linear PQ encoded color value in PQ space in the range [0,1].
๐ญ๐ซ: The luminance of a displayed linear component in nits.
The luminance of a single colour component (๐น๐ซ, ๐ฎ๐ซ, ๐ฉ๐ซ), means the luminance of an equivalent achromatic signal with
all three colour components having that same value.
124
125. HLG End to End Chain
๐ฌ
Non linear color value, encoded
in HLG space in the range [0,1].
The signal determined
by scene linear light, scaled by
camera exposure in the range [0:1].
The luminance of a displayed
linear component
Scene
Light
Scene-referred
Image Data
HLG OETF
Display
Light
Encoding
Reference Display
HLG
O๐๐๐ โ๐
Decoding
OOTF
HLG EOTF
๐ฌโฒ
๐ญ๐ซ
The luminance of a displayed
linear component
Non-reference
Display Light
Non Reference Display and Environment
HLG
O๐๐๐ โ๐
Decoding
OOTF
HLG EOTF
Reference
No Metadata is needed for
display adjustment
๐ฌโฒ
Other Display and Environments
Display Adjustment
OOTF
Adjust
๐ญ๐ซ
Reference
125
126. Parameter Values
Input signal to HLG OETF
E: Scene linear light signal.
The OETF maps relative scene linear light into the non-linear signal value.
HLG Reference OETF 5a
๐ฌ is a signal for each colour component {๐น๐, ๐ฎ๐, ๐ฉ๐} proportional to scene linear light normalized to the range
[0:1]. 5b
๐ฌโฒ is the resulting non-linear signal {๐นโฒ, ๐ฎโฒ, ๐ฉโฒ} in the range [0:1].
๐ = ๐. ๐๐๐๐๐๐๐๐, ๐ = ๐ โ ๐๐, ๐ = ๐. ๐ โ ๐. ๐๐(๐๐) 5c
Hybrid Log-Gamma (HLG) System Reference Non-linear Transfer Functions
โข Note 5a โ The inverse of this non-linearity should be used when it is necessary to convert between the non-linear representation and the linear representation of scene light.
โข Note 5b โ The mapping of the camera sensor signal output to E may be chosen to achieve the desired brightness of the scene.
โข Note 5c โ The values of b and c are calculated to b = 0.28466892, c = 0.55991073.
๐ฌโฒ = ๐ถ๐ฌ๐ป๐ญ ๐ฌ =
๐๐ฌ ๐ โค ๐ฌ โค
๐
๐๐
๐. ๐๐ ๐๐๐ฌ โ ๐ + ๐
๐
๐๐
< ๐ฌ โค ๐
๐ฌ ๐ฌโฒ
๐ญ๐ซ
Scene
Light
Scene-referred
Image Data
HLG OETF
Display
Light
Encoding
HLG
O๐๐๐ โ๐
Decoding
OOTF
HLG EOTF
126
127. Parameter Values
HLG Input signal to OOTF
E: Scene linear light signal.
The OOTF maps relative scene linear light to display linear light.
HLG Reference OOTF 5i
๐ญ๐ซ is the luminance of a displayed linear component {๐น๐ซ, ๐ฎ๐ซ, ๐ฉ๐ซ}, in ๐๐ /๐๐. 5d
๐ฌ is a signal for each colour component {๐น๐, ๐ฎ๐, ๐ฉ๐} proportional to scene linear light normalized to the range [๐: ๐].
๐๐บ is the normalized linear scene luminance.
ฮฑ is the variable for user gain in ๐๐ /๐๐. It represents ๐ณ๐พ, the nominal peak luminance of a display for achromatic pixels.
๐ธ is the system gamma.
๐ธ = ๐. ๐ at the nominal display peak luminance of ๐๐๐๐ ๐๐ /๐๐. 5e, 5f, 5g
Hybrid Log-Gamma (HLG) System Reference Non-linear Transfer Functions
๐ญ๐ซ = ๐ถ๐ถ๐ป๐ญ ๐ฌ = ๐๐๐บ
๐ธโ๐
๐ฌ
๐น๐ซ = ๐๐๐บ
๐ธโ๐
๐น๐บ
๐ฎ๐ซ = ๐๐๐บ
๐ธโ๐
๐ฎ๐บ
๐ฉ๐ซ = ๐๐๐บ
๐ธโ๐
๐ฉ๐บ
๐๐ = ๐. ๐๐๐๐๐น๐ + ๐. ๐๐๐๐๐ฎ๐ + ๐. ๐๐๐๐๐ฉ๐
๐ฌ ๐ฌโฒ
๐ญ๐ซ
Scene
Light
Scene-referred
Image Data
HLG OETF
Display
Light
Encoding
HLG
O๐๐๐ โ๐
Decoding
OOTF
HLG EOTF
127
128. โข Note 5d โ In this Recommendation, when referring to the luminance of a single colour component (RD, GD,
BD), it means the luminance of an equivalent achromatic signal with all three colour components having
that same value.
โข Note 5e โ This EOTF applies gamma to the luminance component of the signal, whereas some legacy
displays may apply gamma separately to colour components. Such legacy displays approximate this
reference OOTF.
โข Note 5f โ For displays with nominal peak luminance (LW) greater than 1000 cd/mยฒ, or where the effective
nominal peak luminance is reduced through the use of a contrast control, the system gamma value
should be adjusted according to the formula below, and may be rounded to three significant digits:
Hybrid Log-Gamma (HLG) System Reference Non-linear Transfer Functions
ฮณ = 1.2 + 0.42 log10(
LW
1000
)
128
129. โข Note 5g โ The system gamma value may be decreased for brighter background and surround conditions.
โข Note 5i โ The inverse of HLG OOTF is derived as follows:
โข For processing purposes, when the actual display is not known, ๐ถ may be set to 1.0 cd/mยฒ.
Hybrid Log-Gamma (HLG) System Reference Non-linear Transfer Functions
๐น๐บ = (
๐๐ซ
๐ถ
)
๐โ๐ธ
๐ธ ๐น๐ซ
๐ถ
๐๐ซ = ๐. ๐๐๐๐๐น๐ซ + ๐. ๐๐๐๐๐ฎ๐ซ + ๐. ๐๐๐๐๐ฉ๐ซ
๐ฎ๐บ = (
๐๐ซ
๐ถ
)
๐โ๐ธ
๐ธ ๐ฎ๐ซ
๐ถ
๐ฉ๐บ = (
๐๐ซ
๐ถ
)
๐โ๐ธ
๐ธ ๐ฉ๐ซ
๐ถ
129
130. Parameter Values
Input signal to HLG EOTF
๐ฌโฒ: Non-linear HLG encoded signal.
The EOTF maps the non-linear HLG signal into display light.
HLG Reference EOTF
Note 5h:
โข During production, signal values are expected to
exceed the range Eโฒ = [0:1]. This provides processing
headroom and avoids signal degradation during
cascaded processing.
โข Such values of Eโฒ, below 0 or exceeding 1, should not
be clipped during production and exchange.
โข Values below 0 should not be clipped in reference
displays (even though they represent โnegativeโ
light) to allow the black level of the signal (LB) to be
properly set using test signals known as โPLUGEโ.
๐ญ๐ซ is the luminance of a displayed linear component signal {RD, GD, BD}, in ๐๐ /๐๐.
๐ฌโฒ is the non-linear signal {๐นโฒ, ๐ฎโฒ, ๐ฉโฒ} as defined for the HLG Reference OETF. 5h
OOTF[ ] is as defined for the HLG Reference OOTF.
๐๐๐๐ โ๐[] is:
The values of parameters ๐, ๐, and ๐ are as defined for the HLG Reference OETF.
ฮฒ is the variable for user black level lift and:
๐ณ๐พ is nominal peak luminance of the display in ๐๐ /๐๐ for achromatic pixels.
๐ณ๐ฉ is the display luminance for black in ๐๐ /๐๐.
Hybrid Log-Gamma (HLG) System Reference Non-linear Transfer Functions
๐ญ๐ซ = ๐ฌ๐ถ๐ป๐ญ ๐ฆ๐๐ฑ ๐, ๐ โ ๐ท ๐ฌโฒ
+ ๐ท
๐ญ๐ซ = ๐ถ๐ถ๐ป๐ญ[๐ถ๐ฌ๐ป๐ญโ๐
๐๐๐ ๐, ๐ โ ๐ท ๐ฌโฒ
+ ๐ท ]
๐ฌ ๐ฌโฒ
๐ญ๐ซ
Scene
Light
Scene-referred
Image Data
HLG OETF
Display
Light
Encoding
HLG
O๐๐๐ โ๐
Decoding
OOTF
HLG EOTF
๐ฌ = ๐ถ๐ฌ๐ป๐ญโ๐ ๐ฌโฒ =
๐ฌโฒ๐
๐
๐ โค ๐ฌโฒ
โค
๐
๐๐
๐(
๐ฌโฒโ๐
๐
)
+ ๐
๐๐
๐
๐๐
< ๐ฌโฒ
โค ๐
๐ท = ๐
๐ณ๐ฉ
๐ณ๐พ
เต
๐
๐ธ
130
132. Increasing Colour Saturation with Leaving the Overall Tone Curve Unchanged in HLG
โ The HLG OOTF (system gamma applied on luminance) uses scene-referred camera signals that result in a
display that closely preserves the chromaticity of the scene as imaged by the camera.
โ This differs from the traditional colour reproduction provided by the HDTV and UHDTV OOTFs, which
produce more saturated colours which viewers of existing SDR content have become familiar with.
Traditional Colour Reproduction for Camera Signals
HLG HDR firmware
1000 nits peak
luminance
HDR Signal
Scene-referred Camera Signals
It preserves the
chromaticity of the scene
SDR Mode
(ITU-R BT.1886, 100
nits peak luminance)
SDR Signal More Saturated Colours
132
133. Increasing Colour Saturation with Leaving the Overall Tone Curve Unchanged in HLG
โ The effect of applying following processing is to increase colour saturation whilst leaving the overall tone
curve unchanged.
Traditional Colour Reproduction for Camera Signals
Applying gamma separately to
red, green and blue components:
It does two things:
โข Firstly, it adjusts the
overall tone curve.
โข Secondly, because it is
applied separately to the
colour components, the
colour saturation is
increased.
Applying an inverse gamma (๐พ= 1/1.2) to the luminance component:
โข It undoes the modification of the tone curve by applying an inverse gamma (๐พ=
1/1.2) to the luminance component of the signal.
โข Applying gamma to the luminance component only (as in the HLG OOTF) leaves
the ratio of the red to green to blue components unchanged and, hence, does
not change the saturation.
โข Conversely, it would be possible to use similar processing to modify a signal
representing the traditional look to instead more closely represent the
chromaticity of the scene as imaged by the camera.
Inverse Gamma
Scene
Light HLG OETF
Encoding
๐ธ = ๐. ๐ Applied on
R, G, B
๐ธ = ๐/๐. ๐ applied
on Luminance
HLG Scene-
referred Signal
Saturation
overall tone curve is change.
Saturation
overall tone curve is unchanged
133
134. โ The HLG signal characteristic is similar to that of a SDR camera with a โkneeโ and no production metadata
is requires.
โ HLG is not specified for use with metadata, and instead has a specified relationship between overall
system gamma (implemented as part of the display EOTF) and peak display brightness.
โ An overall system gamma of 1.2 is specified for HLG when displayed on a 1,000 nit monitor.
a = 0.17883277
b = 0.28466892
c = 0.55991073
Linear Scene Light
Signal
Level
SDR OETF
SDR with Knee
HDR HLG OETF
Relationship Between Overall System Gamma and Peak Display Brightness
HLG HDR Display
1000 nits
HDR Signal
๐ธ๐บ๐๐๐๐๐ = ๐. ๐
134
135. โ In HDR TV, the brightness of displays and backgrounds/surround will vary widely, and the system gamma
will need to vary accordingly.
1- NHK indoor test scene for a 1000 nits reference display and 2000 nits display:
โ Lighting was adjusted so that the luminance level of the diffuse white was 1200 ๐๐/๐2
.
โ The subjects were requested to adjust the system gamma and camera iris with reference to the real scene so that
a tone reproduction similar to the scene could be obtained on the display.
โข For a 1000 nits OLED display (Sony BVM-X300) the average optimum system gamma was found to be 1.18
โข For a 2000 nits peak luminance LCD display (Canon DP-V3010), the average preferred system gamma was 1.29
Appropriate System Gamma, Test 1
Sony BVM-X300 OLED display, 1000 nits
HLG HDR Display
1000 nits
HLG HDR Display
2000 nits
Canon DP-V3010 LCD display, 2000 nits
HDR Signal
System Gamma
Changing
Camera Iris
Changing
Target: A Similar Tone Reproduction to the Scene
by HDR Displays with Different Peak Luminances
135
136. โ In HDR TV, the brightness of displays and backgrounds/surround will vary widely, and the system gamma
will need to vary accordingly.
2- BBC tests for delivering the best compatible SDR image:
โ Similarly, the BBC conducted subjective tests to determine the value of system gamma that delivers the best
compatible SDR image (backwards compatibility with SDR displays).
โข The value of system gamma that delivers the best SDR compatible picture with a 1000 nits display was 1.29
โข The value of system gamma that delivers the best SDR compatible picture with a 500 nits display was 1.18
Appropriate System Gamma, Test 2
Sony BVM-X300 OLED display in SDR mode
SDR Mode
(ITU-R BT.1886, 100
nits peak luminance)
HLG HDR firmware
500 nits peak
luminance
Sony BVM-X300 OLED display in HDR mode
System Gamma
Changing
Camera Iris
Changing
HDR Signal
HLG HDR firmware
1000 nits peak
luminance
Sony BVM-X300 OLED display in HDR mode
SDR Signal
Target: To deliver Best Compatibility SDR Image
by HDR Displays with Different Peak Luminances
136
137. โ In HDR TV, the brightness of displays and backgrounds/surround will vary widely, and the system gamma
will need to vary accordingly.
1- NHK indoor test scene for a 1000 nits reference display and 2000 nits display:
โข For a 1000 nits OLED display (Sony BVM-X300) the average optimum system gamma was found to be 1.18
โข For a 2000 nits peak luminance LCD display (Canon DP-V3010), the average preferred system gamma was 1.29
2- BBC tests for delivering the best compatible SDR image:
โข The value of system gamma that delivers the best SDR compatible picture with a 1000 nits display was 1.29
โข The value of system gamma that delivers the best SDR compatible picture with a 500 nits display was 1.18
Result: Appropriate System Gamma
When designing the HLG HDR system, it was considered more important to weigh the
choice of gamma value in favour of HDR production, rather than backwards compatibility
with SDR displays. So a value of 1.20 was adopted for the reference 1000 cd/mยฒ display.
137
138. Reference Peak
Brightness
Display
Non-Reference
Peak Brightness
Display Test subjects were asked to perceptually match as
closely as possible an image by adjusting the system
gamma applied to the non-reference brightness image.
(in a fixed background luminance of 5 nits)
Gamma
Changing
The pictures from HDR linear light
images from Mark Fairchildโs HDR
Photographic Survey (Image
peak luminance are different).
โ From Previous Tests The system gamma needs to vary according to display peak brightness.
โ New Tests The system gamma needs to vary according to image peak luminance's.
Two tests have been done:
Test 1: corresponds to peak luminances from 1000 to 4000 cd/mยฒ
Test 2: from 100 to 1000 cd/mยฒ
โข Both tests are normalised so that gamma=1.2 at 1000 cd/mยฒ
Appropriate System Gamma, Test 3
Target: to Match Images with Different
Peak Luminance with HDR Displays with
Different Peak Luminances
138
139. Test 1 corresponds to images with peak luminances from 1000 to 4000 nits.
Test 2 corresponds to images with peak luminances from 100 to 1000 nits.
Both tests are normalized so that gamma=1.2 at 1000 nits.
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
100 1000
Gamma
Peak image luminance in cd/m2
Test 1
Test 2
ITU
Rec BT.2100 Note 5e: ๏ง = 1.2 at the nominal display peak luminance of 1000 cd/mยฒ.
Gamma
Appropriate System Gamma, Test 3
Target: to Match Images with Different
Peak Luminance with HDR Displays with
Different Peak Luminances
๐ = ๐. ๐ โ ๐ฟ )
๐๐จ๐ ๐(๐ณ ฮค
๐ ๐๐๐๐ ฮบ = 1.111
๐ธ = ๐. ๐ + ๐. ๐๐ ๐๐๐๐๐(
๐ณ๐พ
๐๐๐๐
)
๐ณ๐พ
400 cd/mยฒ to 2000 cd/mยฒ
139
140. โ Bringing together the results of all studies, it is found that the appropriate system gamma (๐) for different
brightness displays, in the reference environment, can be determined using the following equation:
๐๐ : Nominal peak luminance of the display in nits
โ According to the subjective tests conducted by the BBC, displays for a range of different values of
nominal peak luminance, specifically the range from 400 cd/mยฒ to 2000 cd/mยฒ, can be shown to provide
a consistent look by varying the value of gamma in the HLG OOTF in accordance with the equation
above.
โ This allows programmes to be made using displays with different peak luminance.
๐พ = 1.2 + 0.42 ๐๐๐10(
๐ฟ๐
1000
)
Appropriate System Gamma for Different Brightness Displays (Reference Environment)
140
141. โ Outside this range of peak luminance (Outside 400 cd/mยฒ to 2000 cd/mยฒ) the match of this simple model
to the experimental detail starts to deteriorate.
โ An extended model, โExtended Modelโ illustrated in the figure ., is given by:
โ This may be used for displays with peak luminance outside the range above (outside 400 cd/mยฒ to 2000
cd/mยฒ).
โ Within that range the two models are virtually identical and will provide equally good performance.
โ It should be noted that using a gamma adjustment to adapt to different peak luminances has its
limitations.
โข Television receivers typically apply different and more sophisticated methods.
โข The acceptability of displays with different peak luminance values is a decision for individual
producers, and might differ between productions.
๐ = ๐. ๐ โ ๐ฟ )
๐๐จ๐ ๐(๐ณ ฮค
๐ ๐๐๐๐ where: ฮบ = 1.111
Appropriate System Gamma for Different Brightness Displays (Reference Environment)
141
142. โ The luminance on a production monitor corresponding to nominal peak, 100%, signal level, should be
adjusted to a comfortable level for the viewing environment.
โ The nominal peak luminance of 1000 ๐๐ /๐๐
, identified in Recommendation ITU-R BT.2100, has been found to
work well in typical production environments.
โ The system gamma value may be decreased for brighter background and surround conditions.
Appropriate System Gamma for Non-Reference Environments
OB truck Studio
HLG HDR Display
1000 nits Peak
luminance
Nominal peak signal level (100% signal level) does not have to be set to the peak
luminance of the monitor, which may be too bright for comfortable viewing.
E.g. by decreasing system gamma we set nominal peak signal level to 950
nits to compensate for the differences in the adaptation state of the eye.
HLG Signal
5 cd/mยฒ
142