We actually know that the cone functions are not universal. Obviously, we know some people are colorblind, but there are degrees of colorblind. We are (if I remember correctly) five different variants on the gene for the chromophore in the long wavelength cones and two variants for the middle wavelength cones. As we age, the cones get yellower. All the color matching experiments have concluded that the cone functions of people with normal vision vary somewhat.

Thank you. I'm glad it was appreciated. My quick answer about OKLab is that is lives up to its name! It fixes some of the problems with CIELAB by being based on the cones rather than the silly 1931 Standard Observer. It is nice in that it is very simple. For image processing applications, where operation count can be important, it makes sense. (Or maybe not... processors are pretty darn fast.) The big disadvantage is that they chose to use the square root as the nonlinearity function. Munsell initially tried this in 1905 and it failed. His son improved on that in the 1920s. As a result, when it comes to predicting people's perception of the difference between two colors (deltaE), it is basically on par with CIELAB. CAM16-UCS is currently the most accurate predictor of color difference, but it is on the end end of spectrum in terms of complexity. It has all the fiddly knobs that a researcher could want, but for evaluating of color in industry, a lot of those knobs just need to be nailed down. At this time, I don't know for sure what the best answer is/will be.

I am glad I could help.

Yes. I have done exactly that in a few papers already. :)

Hmmm... I see that the sound is only recorded on one channel. I will try to fix that in the MP4 and re-upload.

I fixed this, but RU-vid won't let me just replace the video. I have uploaded the version with better audio here: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-ZGE_G9WMFWA.htmlsi=V9zIWVIyF2Hw_n4X

There are many efforts by lots of people. I think there needs to be one concerted effort by a group of people!

I might have skipped over that. Sorry. "Specular" refers to light that reflects from a surface without interacting with the surface.

Yes. If one sheet is 1 DE too light, and another is 1 DE too dark, then both will be in tolerance, but they will be 2 DE apart. That's the worst case... generally the differences between two sheets will be smaller. Is there a way around this? Ummm... you could make your production tolerance 0.5 DE. (Yes, I know. Stupid answer!) One approach that the CGATS folks were advocating is kind of a "creeping target" solution. The brand owner (or whoever) decides on a target color. You get to press, and do your best at color OK. You are not exactly at the target, but you are in tolerance. The color at the press OK is now taken as the target for the rest of the run. Now you run into the same sort of issue as you mentioned. The press OK sheet is in tolerance, and the goalposts were moved (by the ref!) so that the new tolerance range is centered on the OK sheet And you can have this 1 DE + 1 DE issue. I kinda think this is hokey, but that's just my opinion. Personally, I like to think of the original target color as being the target color. The goal at press should be to match the original target color, and not the press OK sheet. Does this help?

Thanks John, yes it's a difficult task, to ask a printer or a different shift printer to match the original target and at the same time to match the previous run! It wouldn't be a big issue if tolerance is Delta E 1.. but we are working with delta E 2 for spots colours.. so difference between runs can be really noticeable. Thanks anyway, I guess it's one of those things that we need to live with..

@@rafograph854 1) There isn't a lot of color science behind the Pantone books.... Well, it took a bit of deep math to do the original formulations and it takes a bit to make sure the color is right, but the organization of the book is a haphazard accretion over the decades. 2) Some definitions here: The Planckian locus is the collection of all spectra that can be emitted by a mass that is emitting light strictly because it is really hot. Positions on the Planckian locus are designated by how hot something has to be to create that spectrum. They are always measured in Kelvin, which is 273.16 degrees different from Celsius. 5000 degrees K is equal to about 4,727 degrees C. (The term 5000K is ambiguous, cuz K could mean 1,000 or it could mean degrees Kelvin. That's why we say D50 and D65.) A light can have a "correlated color temperature" of 5000K. This means that it the closest *color* on the Planckian locus is a mass at 5,000 degrees Kelvin. It could be an unnatural shade of green and still have a correlated color temperature. Note the use of the word "color". The spectrum can be whatever, so long as the color of the light looks something like D50. This is normally what we mean when we say a light is 5000 degrees K. D50 and D65 are further tighter definitions. The designation is only applied if the correlated color temperature is sufficiently close to the Planckian locus, and if some other specs are met. I don't recall them specifically (they have changed in the past ten years), but they can be found in ISO 3664.

@@JohnSeymourTheMathGuy thank you very much for the detailed information. Best regards

I will provide a quick explanation here, and ponder a more complete one later. DE00 and DECMC are similar in performance. DE00 edges the other formulas out when looking against the official data sets. In my humble opinion, the improvement is marginal. This was not intentional, but the way the math works, DECMC kind of assumes that one of the colors is the target color and the other is the potential match. The difference between color 1 and color 2 is not necessarily exactly the same as the difference between color 2 and color 1. DE00 fixed this. The color difference data sets showed some weird behavior in the blue region. As a result, they developers added a band-aid. All of the ellipses in DECMC are oriented with the long axis along the hue line. One set of color difference observations showed a tilted ellipse in the blue, so DE00 added a fudge factor to fix this. (In my opinion, they messed up. I predict that there will be similar tilts in the red/orange region and somewhere in the yellow/green. These just haven't shown up in test data. The whole thing could have been fixed by fixing CIELAB rather than fixing color differences. In DECMC, the tolerance regions are true ellipsoids. In DE00, they are ovoids. They are slightly fatter at the high chroma end.

Very reasonable question! My own stubborn and narrow-minded approach is to continue plodding forward with my own math. :) There have been a number of LMS color spaces developed, with the various CIECAM models having the most press. Technically, these are "color appearance models", which means that they take into account the adaptive state of the eye, the intensity of the illumination, and the surrounding colors. All very worthy things if you want to understand how people see color. My gut feel is that this model might be overkill for industrial uses. All that extra capability may make it too hard/confusing. Or maybe that could be helpful? I am hoping that there can be discussions among a diverse collection of industry experts to help answer that question.

@Pranesh Kumar Tough questions... at least for me! Let me start by making it clear. To put my response in context, I claim expert-level knowledge in "what is wrong with CIELAB", but I do not claim expert-level knowledge in the alternatives. My one claim is that basing the color space on LMS rather than XYZ would solve many of the problems with CIELAB. So, any reasonable alternative must be based on LMS. I **think** that CIECAM16 might be the best approach available today, but I have not investigated it in depth. The CIECAM series includes a number of knobs for adjusting to lighting conditions and adaptive state of the user. This is obviously a good thing for the researcher and others who need the most accurate models. This is a issue, on the other hand, for the color manufacturing industry, since it adds the complication of "which knobs should I use". In my somewhat limited view of the world, I would look the Mark Fairchild as the guy. While not an easy read, his book "Color Appearance Models" is as readable as any that I have seen.

I would say that a serious improvement to CIELAB is not for the faint of heart. I have spent a decade or so, in my spare time, trying to understand the causes of the foibles of CIELAB in order for them to be properly compensated for. I do not have anything quite yet that I am ready to recommend. And it what I develop may not substantially differ from CIECAM with a set of fixed parameters.

@@JohnSeymourTheMathGuy surely it would make more sense -rather than focus on the foibles of CIELAB to go back to first principles and make direct use of the present knowledge of the cone functions and modern computational techniques to develop a colour space that meets the needs of modern emissive devices, and digital (computational) devices. Build a better bike, rather than poke holes in the tires of the old bike. The old tristimulus bike’s primary utility in this process would merely be to aid in avoiding the same pitfalls. But if the new colour model accurately centric manipulation of colour. I would like to suggest the mechanism of adoption of the better colour model bike is not through the established, somewhat stagnant print industry with billions in sunk capital and industry training, but rather within the motion picture and broadcast industries (including web, and gaming industries which are based around emissive display technologies). Innovation within these industries - especially motion picture (broadcast) and gaming industries is such that consumer content and hardware purchased a decade ago is barely/ usable today (unlike the print industry in which the mechanism of reproduction has barely changed in half a century, with modern presses often being nothing more, than a bolt on unit and ink refresh added to an 80 year old press. A motion picture camera from 2012 is barely useable in a modern postproduction workflow in the absence of a cobbled together hardware/software from several generations. Innovation is baked into the motion picture industry, and I guarantee that next years blockbuster that wins the awards will not use the hardware used by todays. The post production software will likewise be radically upgraded to accommodate the camera’s capabilities, and will indeed be a generation a head of the capabilities of consumer display technologies, but will adapt the camera vision as best it can to the needs of both the director, and the consumer. Those colour professionals in the post production phase actively bounce between different colour space models (at different levels of skill and experience) in an attempt to translate the directors vision, and the media to what can be viewed on consumer displays, with the least loss of perceptual values. They are very open to better colour models that minimise the effort required to creatively express the vision, via better math. The industry is in the process for instance of adopting three primaries colour models in the processing pipeline that encompass colours outside the visible spectrum just to be able to better recompress the workspace to consumption. But of course in the workspace this wider gamut is not visible to the colourist, and the colourist must needs manipulate colour within models that can not be fully reproduced on their screens, or within their vision. However, they are well aware that some 3 suit one model rather than another. CIELAB is a model that some suggest is best used as the basis for mapping a coloured image to greyscale, so as to achieve a more natural representation of luminance. Lab is also used to generate colours in vfx compositions. But this pretty much relies on the assumption of D65 illumination, and limits the delivered product to consumers, and much of the colourists job is doing workarounds so as to trick the consumers brain into seeing colourfulness and contrast in the way the director intended within the frame of variations of RGB delivered on the basis of D65, and relatively low emissive light levels. This of course is changing rapidly, but the constraints remain. A better colour space model that in the short term enables more efficient colour “correction” will facilitate wider adoption as an industry standard in the motion picture /broadcast/web/gaming industries far far sonnet than in the print industry which will continue to use CMYK and Pantone (maybe not Pantone now that it’s use is moved to a rental model) for the our foreseeable lifetime. I suggest refocusing from documenting holes in CIELAB, to building a model based on cone values. One whose math can be efficiently linearly mapped to the wide gamut colour spaces used in ACES and DaVinci Wide Gamut workflows. Having better (even if still imperfect) human centric colourspace that’s actually works correctly, adopted by the motion picture industry would deliver the fastest uptake, and widespread critique imaginable, leading to further development. Especially if it could be adopted into contemporary display technologies with little industry effort to sell more consumer units. A royalty on consumer devices of 1 cent per thousand consumer units would make you a very wealthy man in your retirement. I suggest collaboration with the colour scientists within the motion picture/broadcast industries who are developing DaVinci Wide Gamut (Blackmagic Design) and ACES (The Potion Picture Academy) -they are both actively engaged with the development of next years hardware and software that will set the standard, and all of those in that industry are obsessed with delivering better colour reproduction to consumers, and it is they who are leading the broader consumer manufacturing industry to higher standards. Meanwhile the print industry, is merely obsessed with maximising per page profits, by reducing the cost of the inks, and “papers” having settled on a long since standardised hardware regime. Any improvements in colour reproduction in the print industry in recent decades has been on the back of the developments in film, and digital technologies used in the motion picture industries, but knee capped by the limitations of delivering to a physical medium which hasn’t much changed for centuries.

@@johnprivate6625 I appreciate the insight into an industry that I have little expertise in!

A polarizing filter can either increase or decrease the specular light, depending on the rotation of the filter. For three dimensional objects, this can make them appear flatter, since the brain doesn't get that extra clue about shape. On the other hand, eliminating the specular can make the colors of a flat object appear richer - which may be a desirable effect. One photographer I spoke with prefers a polarizing filter when doing (painted canvas) reproductions. Let me know what you find out!

That's a good question, but I don't feel qualified to answer it! I don't have enough experience with HSP to know if it did fix the problem. I am inclined to think that throwing more equations at XYZ is simply added a band-aid to a pimple on a wart. If HSP goes back to LMS, then they are heading in what I think would be the right direction. I welcome anyone else to offer a more informed opinion.

Sorry for the confusion. Patch #3 had a reflectance of about 50%. Half the light reflects.

Actually... it would be pretentious to point out that when you compare two data sets (each with one member) the Mahalanobis distance calculation is undefined. Recall that variance and covariance are calculated by first subtracting the mean from the data. This gives a variance-covariance matrix which is all zero, and cannot be inverted. If I were really pretentious, I might point out that Hotelling's T-square statistic is the square of the Mahalanobis distance, since this doesn't seem to be commented on very often. Glad to see you watched the whole video!