3. What is HDR?
HDR is high-dynamic-range
imaging (HDRI or just HDR)
4. Why HDR?
With HDR technology, we can have a
greater dynamic range of luminance
between the lightest and darkest
areas of an image than current
standard digital imaging techniques
or photographic methods (Wikipedia)
10. The world is high
dynamic range
Luminance
Type of light
(candela/m^2)
Light from a star 0.001
Light from the moon 0.1
Inside a house 100
Light from the sun 100000
11. The Dynamic Range of
an Image
The Dynamic Range of an image is the
capacity of this image to restitute
the correct intensity scales we can
observe in the real world
We often express the dynamic using
the “stops” unit
13. In digital photography
JPEG file: 256:1 ratio giving 8 stops
RAW file: generally 10 bits: 10 stops
HDR file: This depends on the file
itself but can go way over 15 or 20
stops.
14. Comparison
The real world: total range of
100,000,000 corresponding to 26 stops
A standard digital file (jpeg or
raw): 10 stops maximum
16. So how to reserve
information?
capturing the entire dynamic of the
scene with a very limited sensor in
terms of dynamic range
Various techniques were invented to
achieve this goal
the most used is to take several
pictures of the same scene using
different exposure values
19. radiance E falling on sensor location
i and the exposure time Δt to produce
value C at pixel i
Ci = f (Ei ∆t)
20. g the natural log of the invertible camera
function
Zmin and Zmax pixel value boundary
N number of samples
P number of photographs
w a ‘hat’ weighting function (encourages the
smoothness of g )
N P Zmax −1
O= w(Cij )[g(Cij − ln Ei − ∆tj ]2 + λ w(z)g n (z)
i j z=Zmin +1
minimize to find range of g
21. Once the matrices of coefficients
have been initialized, two lines of
MATLAB code solves this system of
equations using Gaussian elimination:
X=Ab;
g=X(1:256);
22. With g fully determined by a lookup
table
reconstruct the radiance map by
combining the exposures, using a
weighted average of the camera
response function of the pixels in
each exposure (N total pixels in
image)
P N
j=1 i=1 w(Cij )[g(Cij ) − ln ∆tj ]
ln Ei = P
j=1 w(Cij )
24. HDR Images Format
Available high dynamic-range formats:
-Radiance 32-bit RGBE and XYZE pictures
-TIFF 48-bit integer and 96-bit float
formats
-SGI 24-bit and 32-bit LogLuv TIFF
-ILM OpenEXR format
-JPEG-HDR format
Proposals and extensions:
-HDR extension to MPEG from MPI
[Mantluk et al. 2004]
-HDR extension to JPEG 2000 from UFL
[Xu et al. 2005]
-HDR texture compression
[two paper at SIGGRAPH 2006]
29. HDR Displays 1
Y Axis
0
-6 -4 -2 0 2 4 6 8
starlight moonlight indoor lighting sunlight
X Axis
Human Simultaneous Luminance Vision
Range
Today’s Devices
30. HDR Displays 1
Y Axis
0
-6 -4 -2 0 2 4 6 8
starlight moonlight indoor lighting sunlight
X Axis
5 orders of magnitude
Human Simultaneous Luminance Vision
Range
Today’s Devices
31. HDR Displays 1
Y Axis
0
-6 -4 -2 0 2 4 6 8
starlight moonlight indoor lighting sunlight
X Axis
5 orders of magnitude
Human Simultaneous Luminance Vision
Range
Today’s Devices
2-3 orders
32. Design principle for
HDR Devices
Requirements:
1. High Dynamic Range
2. Compatibility
New devices need to function in 8-bit
environment and still deliver
significant benefit
New devices need to be usable in stand-
alone mode
3. Cost
Ideally no extra cost compared to 8-bit
devices
If extra cost is necessary then in line
with benefit
33. Display Technology
Conventional LCD
LCD backlight is provided by CCFL
tubes (fluorescent light)
Light is spread evenly behind LCD
panel and does not vary with image
content
Image control is limited to 8 bit
single to Red, Green and Blue colour
channels (255 steps of control)
34.
35. Display Technology –
HDR Display
LCD backlight is provided by an array of
LED’s
Each LED is controlled with 8 bit (255
step) signal
Brightness is adjusted to level demanded
by source image
LCD panel provides additional 8 bits of
brightness control
LED and LCD panel combine optically to
deliver 16 bit performance
LED’s provide greater brightness
37. 8A<-2):+64200,5-)B7-6+,/.A
HDR Image LED array LCD with correction Output image
!"#$"#%%& '#%%())*+,-./0,12)324.5676-,20)8549)):+6;+,2/<+=)>)?65@,125/,<7)) C%
38. Display Technology
Review
Compatibility
*Based on commercially available
components (LCD, LED)
*Legacy support through Reverse Tone
Mapping and Saturation Extension
*Small number of LEDs allows encoding of
LED data in conventional video signal
Cost
*LED cost money (less every day)
*Significant power reduction (~25% of
comparable constant backlight LCD on
average)
39. HDR devices
HDR Displays are available
HDR Projectors are coming
HDR Output Devices can provide
benefit to legacy content
HDR Software / Input Devices are
leading the way
41. Tone Mapping
Tone mapping reduces the dynamic range, or
contrast ratio, of the entire image, while
retaining localized contrast (between neighboring
pixels), tapping into research on how the human
eye and visual cortex perceive a scene, trying to
represent the whole dynamic range while retaining
realistic color and contrast.
Images with too much tone mapping processing have
their range over-compressed, creating a surreal
low-dynamic-range rendering of a high-dynamic-
range scene.
44. Techniques
Only a few fundamentally different
approaches to tone reproduction exist
-Based on image formation
* Frequency domain
* Gradient domain
-Based on the human visual system
* Global operators
* Local operators
48. Image Based Lighting
Image-based lighting (IBL) is a 3D
rendering technique which involves
plotting an image onto a dome or
sphere that contains the primary
subject. The lighting characteristics
of the surrounding surface are then
taken into account when rendering the
scene, using the modeling techniques
of global illumination. This is in
contrast to light sources such as a
computer-simulated sun or light bulb,
which are more localized.
59. HDR Rendering
In 3D computer graphics, high-dynamic-range
rendering (HDRR or HDR rendering), also known as
high-dynamic-range lighting, is the rendering of
computer graphics scenes by using lighting
calculations done in a larger dynamic range. This
allows preservation of details that may be lost
due to limiting contrast ratios. Video games and
computer-generated movies and special effects
benefit from this as it creates more realistic
scenes than with the more simplistic lighting
models used.
Graphics processor company NVIDIA summarizes the
motivation for HDRR in three points:
1) bright things can be really bright
2) dark things can be really dark
3) details can be seen in both.
60.
61. Applications in computer
entertainment
Currently HDRR has been prevalent in
games, primarily for PCs, Microsoft's
Xbox 360, and Sony's PlayStation 3. It
has also been simulated on
thePlayStation 2, GameCube, Xbox and
Amiga systems. Sproing Interactive Media
has announced that their new Athena game
engine for the Wii will support HDRR,
adding Wii to the list of systems that
support it.
62. GPUs that support HDRR
the minimum requirement for HDR
rendering is Shader Model 2.0 (or in
this case DirectX 9), any graphics
card that supports Shader Model 2.0
can do HDR rendering. However, HDRR
may greatly impact the performance of
the software using it if the device
is not sufficiently powerful.
83. Future Work
HDR technology is relatively new
Faster HDR Algorithms
Better HDR formats for images and
videos
Cheaper and better HDR displays
Movies and Games with HDR
