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Oklab: A perceptual color space for image processing

bottosson.github.io

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Re: Oklab: A perceptual color space for image processing

#21

Post by bjornornorn »

mkl wrote: post #16
bjornornorn wrote: post #6

Earlier quoted context omitted.

Author here. Wow, thanks a lot! If anyone has any questions feel free to post here and I can try to answer. I have another post that goes into more detail onhow software often gets color wrong: https://bottosson.github.io/posts/colorwrong/

It's a great article, and an interesting new colour space. It would be really interesting to see a variety of image transformations done in each of these colour spaces, on a variety of images (photos in particular). E.g. resizing and blurring as jiggawatts suggests, and also things like brightness, contrast, saturation, white-balance, etc. How big are your datasets? Would the parameters get better if they were bigger…

Yeah, would be nice. I've been thinking a bit about following up with that.

The generated dataset consists of a few thousand colors. The hue dataset is using 15 different hues only. Some more data there could definitely be useful.

I think the biggest problem is that there isn't that much experimental data overall, especially for wide gamut colors. The hue data is from experiments with sRGB displays if I remember correctly, and CIECAM I think has mostly been derived based on surface paints, which makes it fairly limited.

Comprehensive experiments done using modern calibrated wide gamut displays would be fantastic.

Thanks, will have a look at the typos!

Re: Oklab: A perceptual color space for image processing

#22

Post by JyrkiAlakuijala »

This looks very similar to what I came up for pik, consequently used as main default colorspace of JPEG XL, i.e., XYB.

Also butteraugli's XYB has similar ideas, but is slightly more expensive to calculate due to the biased logarithm in the compression function (instead of cubic root), but possibly scales better for HDR (say above 200 nits).

JPEG XL's XYB includes more red and less green in S-receptor modeling (for the blue-yellow axis). If I look at literature of LMS receptor spectra, it makes me wonder why there is so much green in Oklab. When I optimized similar for XYB, the optimization would favor adding slightly more red for the S than green.

S component in JPEG XL XYB before non-linearity:

0.24 * R + 0.20 * G + 0.56 * B

S component in Oklab before non-linearity:

0.05 * R + 0.26 * G + 0.63 * B

Given the similarity of Oklab and XYB I suspect (but i'm not completely sure) that JPEG XL's format is powerful enough to model Oklab, too. Very very likely it can perfectly model the M1 matrix and the cubic root. I believe for M2 there may be some need for approximations. There JPEG XL can have local variations for M2 from chroma-from-luma fields, but likely luma needs to be slightly different from Oklab.

Re: Oklab: A perceptual color space for image processing

#23

Post by HelloNurse »

dTal wrote: post #5

I don't understand why they don't compare it with YCbCr, which is a very similar colorspace that is much more widely used than some of the obscure ones they compare it with - notably, in JPEG.

YCbCr was designed for the needs of analog color TV transmission and recording, not for image processing and editing.

Re: Oklab: A perceptual color space for image processing

#24

Post by jacobolus »

postingpals wrote: post #8
bjornornorn wrote: post #6

Earlier quoted context omitted.

Author here. Wow, thanks a lot! If anyone has any questions feel free to post here and I can try to answer. I have another post that goes into more detail onhow software often gets color wrong: https://bottosson.github.io/posts/colorwrong/

I've been trying to get into this area of study.. what did you read to know all this stuff?

The best online resource is https://www.handprint.com/HP/WCL/wcolor.html

Or you can buy an introductory color science book or two. Let me recommend Mark Fairchild's Color Appearance Models, https://www.amazon.com/dp/1119967031/ but here are a few others https://www.amazon.com/dp/1119367220 https://www.amazon.com/dp/0470024259 https://www.amazon.com/dp/1118173848/ https://www.amazon.com/dp/0470049049

Re: Oklab: A perceptual color space for image processing

#25

Post by JyrkiAlakuijala »

JyrkiAlakuijala wrote: post #22

This looks very similar to what I came up for pik, consequently used as main default colorspace of JPEG XL, i.e., XYB. Also butteraugli's XYB has similar ideas, but is slightly more expensive to calculate due to the biased logarithm in the compression function (instead of cubic root), but possibly scales better for HDR (say above 200 nits). JPEG XL's XYB includes more red and less green in S-receptor modeling (for th…

Another rather substantial difference is in M2 matrix of Oklab. In my experiments I don't see S-participation in colors with high spatial frequency. Because in image compression a lot of information is in high spatial frequency, one gets favorable image compression when M2 matrix is without S contribution in Luma. We use just [b b 0, a -a 0, -0.5 * c, -0.5 * c, c] in the M2 phase in JPEG XL. The two 0s there don't bring S reception into Luma and redness-greenness observations.

This difference can be because Oklab is based on XYZ which is based on 2 degree color samples. XYB is based on about 0.03 degree color samples. Perception seems to be different there -- to me it looks like S is not yet integrated into Luma experience at that resolution.

In butteraugli color modeling is more complex: it is divided into high spatial frequency and low spatial frequency. S is brought only to the low spatial frequency color transforms. (Frequency separation there is by Laplacian pyramid.)

Re: Oklab: A perceptual color space for image processing

#26

Post by jacobolus »

bjornornorn wrote: post #6
jiggawatts wrote: post #3

This is a tour de force of colour theory, and should be mandatory reading for anyone serious about computer colour! Björn Ottosson not only did some mighty fine work, producing a simple equation that produces smooth colour gradients, but he "showed his work" too. Instead of just journal references, he littered this page with incredibly useful hyperlinks to difficult to find things such as the raw data for the Munsell…

Author here. Wow, thanks a lot! If anyone has any questions feel free to post here and I can try to answer. I have another post that goes into more detail onhow software often gets color wrong: https://bottosson.github.io/posts/colorwrong/

Let me recommend reducing the number of decimal digits in your published forward matrix to 4 or 5. There's no way the extra 5 digits are making a practical difference here, and they make it a lot harder to write down in a visually compact way.

Do it soon before you have too many people creating independent implementations.

Re: Oklab: A perceptual color space for image processing

#27

Post by bjornornorn »

jacobolus wrote: post #24
postingpals wrote: post #8

Earlier quoted context omitted.

I've been trying to get into this area of study.. what did you read to know all this stuff?

The best online resource is https://www.handprint.com/HP/WCL/wcolor.html Or you can buy an introductory color science book or two. Let me recommend Mark Fairchild's Color Appearance Models , https://www.amazon.com/dp/1119967031/ but here are a few others https://www.amazon.com/dp/1119367220 https://www.amazon.com/dp/0470024259 https://www.amazon.com/dp/1118173848/ https://www.amazon.com/dp/0470049049

Yeah, both of those are good recommendations!

I also think it is useful to focus on understanding the various experiments that have led to the different color models. The most important one is the experiments that led to CIE XYZ. Lecture notes from universities seem like one of the best sources of info about the basics. Such as this: https://www.cl.cam.ac.uk/teaching/1516/AdvGraph/02_Light_and...

Other experiments that are interesting, but a bit hard to find information about are: The Munsell renotation effort in the 1940s, the experiments that led to OSA-UCS, the MacAdam ellipses.

I also like this paper since gives a fairly good overview and lots of new keywords to search for: https://www.osapublishing.org/viewmedia.cfm?uri=oe-25-13-151... (and is freely available)

Re: Oklab: A perceptual color space for image processing

#28

Post by bjornornorn »

olivierduval wrote: post #18
bjornornorn wrote: post #6

Earlier quoted context omitted.

Author here. Wow, thanks a lot! If anyone has any questions feel free to post here and I can try to answer. I have another post that goes into more detail onhow software often gets color wrong: https://bottosson.github.io/posts/colorwrong/

Hello Really nice work!!! How does it compare with HSLuv ( https://www.hsluv.org/ )? It seems that both scheme try to manage the perceptual color problem...

That is based on CIELUV, which is one of the spaces tested against in the article. CIELUV is useful because its chromaticity space is a projective transform of XYZ. That also means it doesn't predict perception of hue as well as more complex models.

Re: Oklab: A perceptual color space for image processing

#29

Post by batty_alex »

HelloNurse wrote: post #23
dTal wrote: post #5

I don't understand why they don't compare it with YCbCr, which is a very similar colorspace that is much more widely used than some of the obscure ones they compare it with - notably, in JPEG.

YCbCr was designed for the needs of analog color TV transmission and recording, not for image processing and editing.

Person your responding to isn’t asking about that particular color space. They’re asking for some real-world examples. This is a very theoretical piece about color spaces that intersects with a very particular use of color spaces.

YCbCr was definitely not designed for analog tv. That color space is for digital video and imaging

Re: Oklab: A perceptual color space for image processing

#30

Post by jacobolus »

bjornornorn wrote: post #27
jacobolus wrote: post #24

Earlier quoted context omitted.

The best online resource is https://www.handprint.com/HP/WCL/wcolor.html Or you can buy an introductory color science book or two. Let me recommend Mark Fairchild's Color Appearance Models , https://www.amazon.com/dp/1119967031/ but here are a few others https://www.amazon.com/dp/1119367220 https://www.amazon.com/dp/0470024259 https://www.amazon.com/dp/1118173848/ https://www.amazon.com/dp/0470049049

Yeah, both of those are good recommendations! I also think it is useful to focus on understanding the various experiments that have led to the different color models. The most important one is the experiments that led to CIE XYZ. Lecture notes from universities seem like one of the best sources of info about the basics. Such as this: https://www.cl.cam.ac.uk/teaching/1516/AdvGraph/02_Light_and... Other experiments th…

For those interested in the Munsell system:

Landa & Fairchild 2005, "Charting Color from the Eye of the Beholder", http://markfairchild.org/PDFs/PAP21.pdf

* * *

Nickerson 1940 "History of the Munsell Color System and Its Scientific Application" https://doi.org/10.1364/JOSA.30.000575

1943 OSA Munsell renotations report: https://doi.org/10.1364/JOSA.33.000385

Nickerson 1976 "History of the Munsell Color System, Company, and Foundation" (3 parts) https://doi.org/10.1111/j.1520-6378.1976.tb00003.x https://doi.org/10.1111/j.1520-6378.1976.tb00017.x ahttps://doi.org/10.1111/j.1520-6378.1976.tb00028.x

Nickerson 1983 obituary for Alex Munsell, https://munsell.com/color-blog/alexander-ector-orr-munsell/

Kuehni, "The early development of the Munsell system" https://doi.org/10.1002/col.10002

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