Hue preservation and color correction

HUE PRESERVATION AND
COLOR CORRECTION
- 2 papers with a brief study and practical strategies
a. Color correction for tone mapping, R. Mantiuk, et, al. EuroGraphics 2009
b. Hue preservation using enhanced integrated multi-scale retinex for
improved color correction,Wand-Jun Kyung, et, al. Journal of Imaging Science
and Technology, 2011.
13年7月31⽇日星期三

OUTLINE
• Background and Purpose
• [MMTH09] Color Correction forTone Mapping
• [KLLH11] Hue Preservation using Enhanced Integrated Multi-
scale Retinex for Improved Color Correction
• The Current Color Correction Issues We Deal with

BACKGROUND

COLOR REPRODUCTION /
TONE MAPPING
• For the purposes of displaying in
different devices and get perceptively
matched color when applying effects.
• Tone Reproduction Curve (TRC)
- a global tool which bases on global adaption to adjust the
whole image. simple and efﬁcient.
• Tone Reproduction Operator (TRO)
- is a multi-resolution decomposition algorithm to ﬁnd the
best solution operated in local. precise and preserved
local quality.

COLOR REPRODUCTION /
TONE MAPPING (CONT.)
• TRO has better result, but it also
produces artifact or halo. ex: HDR
mapping.
• AlthoughTRC has no halo or
artifacts, it cannot preserve the local
contrast or saturation.

COLOR CORRECTION
• Both reproduction mechanisms have issue on Color Shift. Or
what we say the color becomes not related to human eyes’
perception.

[MMTH09] COLOR CORRECTION
FORTONE MAPPING

[MMTH09] COLOR CORRECTION
FORTONE MAPPING
• A method which focused on Color Correction with different
contrast compression afterTone Curve Mapping (TRC), and
then extended toTRO.
• Modeled the color reproduction properties and
demonstrated the relation between saturation and contrast
in color matching is not Linear.
• Pointed out the color shift was due to the tone mapping
curve itself.

RELATED WORK
Gamut mapping
• Need modify luminance and
chrominance at the same time to
preserve color appearance.
• P1: For tone mapping, the
luminance is given by curve.
• P2: Gamut mapping corrects
color in small dynamic range. But
tone mapping is not.

COLOR APPEARANCE FACTORS
RELATED WORK ( CONT. )
• Luminance, Hunt Effect [Hun52]
• Image Size [NB06]
• Color of the surround [BM97]
• Perceived contrast of complex
images decreases with reduced
chroma and the relation is
sigmoidal. [CF03]

COMMON APPROACH
RELATED WORK ( CONT. )
• Preserving color ratios of tone mapping [Sch94]
• An ad-hoc formula is to adjust the saturation level by power
s. [TT99]
• How to ﬁnd ﬁnd correct s ?
(1)
(2)

ENHANCEMENT
• The drawback is it alters the resulting luminance for
(3)

THE CONTRAST
Contrast compression
where b is the brightness(exposure) adjustment that
normalizes for maximum display brightness. Under huge
contrast compression, nor equation (2) or equation (3) can
ﬁt good result.
(4)

CONTRAST COMPRESSION
CAUSES BAD RESULTS
(4)

EXPERIMENT
To ﬁnd what the s should be
under different contrast c.

EXPERIMENT
(CONT.)
For equation (2) For equation (3)

1. By Analysis ofVariance( ANOVA ), LDR and HDR has no
statistical difference.
2.The relation between s and c can be approximated with a
power function below for c <= 1.6
3. For general function, a sigmoid function has been proposed:
RESULT
(5)

CORRECTION IN CIELAB
In CIELAB, it almost no need
to adjust saturation in low
contrast compression range,
(0.6, 1.6)

CORRECTION IN CIELAB
(CONT.)
CIELAB seems great. But
it’s hard to be used in high
dynamic range image due
to it’s hard to estimate
reference white color.
So it is only workable in
LDR images.

APPLICATION
•Eq2 model get little un-natured color, but the goal
is the best reference instead of best look.
•Eq3 often results in a hue shift for red colors.

EXTENDTOTRO
•[DD02] proposed a bilateral ﬁltering tone operator
function.This operator uniformly reduces the contrast of
the base layer( low pass + edges) while preserving details.
•To calculate the contrast factor c, can be approximated by
the slope of the tone curve on the log-log plot. which
given by the derivative of the tone-curve in the
logarithmic space.

EXTENDTOTRO
(CONT.)

[KLLH11] HUE PRESERVATION
USING ENHANCED INTEGRATED
MULTI-SCALE RETINEX FOR
IMPROVED COLOR CORRECTION

[KLLH11] HUE PRESERVATION USING ENHANCED
INTEGRATED MULTI-SCALE RETINEX FOR IMPROVED
COLOR CORRECTION
• Aimed on ﬁxing the hue shift issue when extreme lightening a
picture.
• Apply theTRO on CIELAB Space.
• Enhance the downgraded highlight due to normalization.
• Use gamut mapping and gamut extension to solve out of gamut
and desaturation.

BACKGROUND PROBLEM
• To reveal the information which comes from the dark image.
• TRO method can preserve the contrast thanTRC.
An example of lightening but de-contrasting image by r correction (TRC).

RETINEX BASED METHOD
RELATED WORK
• Retinex Basic Operator
Output Image Pixel
Input Image Pixel
L of Input Image Pixel
L of surround pixels

RELATED WORK (CONT.)
• Single Scale (SSR) v.s. Multi-Scale (MSR), the convolution
methods.
SSR
MSR
The distance scale c is scalable

• The MSR Problem, Chroma Shift and Artifact
a. original image, b. background, c. standard MSR under linear space.

IMSR (INTEGRATED)
• It calculates luminance images by
different scale of convolution ﬁlters.
• Merge all of the luminance result can
get a Integrated Surround Image, SR.
• The SR image can be used as weight
mask to adjust the light.
• Better chroma preserving. No
artifact.

IMSR (INTEGRATED)
(1)
(2)
(3)
user param

IMSR ISSUES
1. Lightness
2.The dark region desaturated

PROPOSED METHOD

PROPOSED METHOD
STEP 1. COLOR SPACE
• Transfer Color Space to CIELAB and replace function to
Luminance.
(3’)
(2’)
(1’)

PROPOSED METHOD
STEP 2. LIGHTNESS CORRECTION
• The original problem is due to Normalization.To ﬁx it, use a
cumulative distribution function, cdf to instead it.
Gamut mapping Cdf correction

PROPOSED METHOD
STEP 2. LIGHTNESS CORRECTION - GAMUT (CONT.)

PROPOSED METHOD
STEP 3. SIMPLE HUE EXTENSION FOR SATURATION COMPENSATION

EXP
RESULT

RESULT

RESULT
(CONT.)

RESULT
(CONT.)
q1. hue shift
q2. nature look

OUR ISSUES

TONE IN LIGHTNESS
• The key reason that the
level of highlight tone
cannot be further enhance
might due to normalization
or familiar operation.
• cdf or the curve slope is a
possible solution.

ARTIFACT OF GRADIENT MASK
• The mask now will skip hue
correction if the mask ﬁts
maximum.
• It’s kind of aTRO operation
so that the artifact is almost
inevitable.
• A basic solution is apply hue
correction to whole image.
Or should we separate the
procedures with different
effect ?

TONE CURVE HUE CORRECTION

TONE CURVE HUE CORRECTION
• In extremely tone curve mapping, nature look is based on
human’s perception, It’s hard to provide a general solution.
• Consider the curve slope, ﬁnd an equation model to
1. do tone correction if slope <= k
2. adjust luminance if slope > k, due to the bigger slope
means user applied an extremely adjust, and it might can be
adapted to nature light.
3.TRO with gaussian ﬁlter might be a solution to smooth
img.

VIGNETTE PERFORMANCE
TUNING
• In last version,Vignette Performance was stocked on SSE
tuning due to color correction makes effect quality bad.
• could cdf help to solve the problem?

DOES LR USE SAME ALGORITHM
BOTH INTRC ANDTRO ?
• In the other product, the color correction is a black box we
need to investigate.
• The effect in LR not only includesTRC but alsoTRO. It’s hard
to infer they are all adapted to the same color correction
strategy.
• But how to know ?

THANKS FORYOUR ATTENTION
Alfred

Hue preservation and color correction

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