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Author Topic: DSLR testing sites like DXOmark and Imaging Resource use HMI and LEDs for color  (Read 55951 times)

Jack Hogan

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This?  The Reproduction of Colour 6th Edition.

Or this?  Colour Reproduction in Electronic Imaging Systems: Photography, Television, Cinematography 1st Edition.

This,  Hunt's 'Reproduction' book is outdated imho.

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Jack Hogan

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No one mentioned the camera profile as a factor affecting Delta E numbers.

Hi Tim, that's what the transforms mentioned above are all about.

Jack
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Alexey.Danilchenko

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This,  Hunt's 'Reproduction' book is outdated imho.
They are about completely different topics though.
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digitaldog

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Hi Tim, that's what the transforms mentioned above are all about.

Jack
Sad that once again, we have to point out the obvious....  ;)

Those crappy Delta E numbers as the accepted color match pretty much makes this thread a waste of time.
Please move on and stop waiting your precious time...  :P
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Jim Kasson

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This,  Hunt's 'Reproduction' book is outdated imho.

But a great way to get a historical perspective from the end of the film era. First color science book I bought, in 1990, after Kodak paid a visit to my lab and asked if we were interested in some joint work on color file format standards. It felt kind of outdated (and wandering) even then. Measuring Colour was the Jack Webb, "just the facts, ma'am" alternative (though, as Alexey points out, the thrusts of the two books are different), and I found that a few weeks later.

Jim

WayneLarmon

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This,  Hunt's 'Reproduction' book is outdated imho.

I modified my post to include the 2nd book while Iliah was responding to my original post that only mentioned The Reproduction of Colour 6th Edition.  I don't think that Iliah saw  Colour Reproduction in Electronic Imaging Systems: Photography, Television, Cinematography 1st Edition.

[Edit.  I thought you were referring to Colour Reproduction in Electronic Imaging Systems: Photography, Television, Cinematography 1st Edition.   I just clicked your link.  I just got Measuring Colour 4th Edition (because of Alexey's recommendation earlier in the thread) last Saturday.

I've found that reading multiple books that converge around the same subject helps.  Convergence is sublime.]

Wayne
« Last Edit: June 25, 2018, 02:23:48 pm by WayneLarmon »
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Doug Gray

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I've found that reading multiple books that converge around the same subject helps.  Convergence is sublime.]

Wayne

Absolutely!  I found that approach much faster overall as far back as when learning calculus and linear systems. One learns by making connections and sometimes a text will poorly communicate some ideas where another will do an excellent job. Each has their strengths and weaknesses. So I've used the same technique ever since. You wouldn't believe the number of books I have on error correcting codes, programming, signal processing, and general tech stuff.
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Tim Lookingbill

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But a great way to get a historical perspective from the end of the film era. First color science book I bought, in 1990, after Kodak paid a visit to my lab and asked if we were interested in some joint work on color file format standards. It felt kind of outdated (and wandering) even then. Measuring Colour was the Jack Webb, "just the facts, ma'am" alternative (though, as Alexey points out, the thrusts of the two books are different), and I found that a few weeks later.

Jim

Nice to hear from someone in the color film business giving some background on the progress of photographic color reproduction.

Jim, do you see a huge improvement in the digital world? I do. And I don't need all this splitting hair measuring and use of obscure definers to determine color is precisely being reproduced digitally?

At least one thing that helped me in this thread is Wayne's posting of the French's mustard bottle images going from greenish to reddish as it related to the measured CRI numbers using a spectro. It at least showed a connection that the measuring device was actually showing the effects of the spikes in various LED spectra that's difficult to see perceptually.

And we don't judge the accuracy of color reproduction of images by comparing the original side by side with the reproduction like checking Delta E/Lab numbers A/B'ing individual color patches. So I don't see the usefulness of checking for precise by the numbers comparisons this way. It's a waste of time.

I'm surrounded by a community of fine art painters who have outside vendors provide reproduction prints of their paintings from artist provided digital captures, some with cellphones, others with P&S and DSLR's. None of these artists complained about color matching to the original.
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digitaldog

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And we don't judge the accuracy of color reproduction of images by comparing the original side by side with the reproduction like checking Delta E/Lab numbers A/B'ing individual color patches. So I don't see the usefulness of checking for precise by the numbers comparisons this way. It's a waste of time.
I suspect most people who don't understand basic colorimetry or have the tools to evaluate it, nor measure an illuminant and analyze it (the discussion here) would feel the same way.
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Jim Kasson

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Jim, do you see a huge improvement in the digital world? I do. And I don't need all this splitting hair measuring and use of obscure definers to determine color is precisely being reproduced digitally?

I'm not knocking the talents of the brilliant chemical and industrial engineers at Kodak, Agfa, Fuji, and many other companies. It's just that it is really hard to produce a film/processing -- in the case of 'chromes -- and film/processing/paper/processing -- in the case of color negative films and papers -- system that produces accurate color. At SPIE meetings Ed Giorgianni, a Kodak engineer of some repute, used to give seminars on the details of the color processing of film-based systems. I would walk out shaking my head, amazed that film did as well as it did, considering all the really tough chemical problems involved.

I once did an experiment where I took 25 different 'chrome emulsions (this was in the 90s, when there were lots to choose from), shot a Macbeth chart, and read all the resultant patches with a spectrophotometer. The average CIEL*a*b* delta-Es were in double digits. By the way, the great thing about doing that experiment was smelling film canisters right after I opened them. I loved that smell, and miss it in the digital age.

The engineers working on film systems weren't dummies. They knew they couldn't make it accurate. There was a body of opinion that stated that you didn't want it accurate even if you could do it. So they came up with many clever and artful inaccuracies that we call the film look. But it's not one look, it's a bunch of looks, and none of them are very accurate. Now we have digital systems, and we have less constrictions on what we can do. It's still impossible to build practical systems for color photography with perfect accuracy, but what we have now is much better than with film.

Jim

Tim Lookingbill

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I once did an experiment where I took 25 different 'chrome emulsions (this was in the 90s, when there were lots to choose from), shot a Macbeth chart, and read all the resultant patches with a spectrophotometer. The average CIEL*a*b* delta-Es were in double digits. By the way, the great thing about doing that experiment was smelling film canisters right after I opened them. I loved that smell, and miss it in the digital age.

I share your love for the smell of opening a fresh film canister, but back in the '80's I had to often hold my breath to avoid the musty old chemical smell cracking open the film advance compartment in my used Yashica SLR I bought at a pawn shop in Austin, Tx. There was some weird kind of chemical/mixed metal corrosion going on that had the foam seal crumbling in my hands every time I dropped in a role of film.

I do think digital might be too good at color reproduction that raise unrealistic expectations for reproduction on inkjet prints for some "Southwest Art" style artists who want to reproduce the brilliant oranges, yellows and tans in their acrylic paintings viewed under halogen lights. It's sort of a fluoresce effect that I had to assume some inkjet printed inks can't reproduce.

A local art gallery curator emailed me back in 2006 to help him get a print match from the scans of these Southwest Art paintings and I didn't know enough about how the quality of light one views paintings under has limitations when digitally captured. The scans were just butt ugly and so were the prints compared to how the original looked under the halogen. The curator resorted to using a DSLR but he lit the painting with a daylight balance CFL which still couldn't reproduce the eye popping vibrance of the originals provided by the halogen lights.

I've posted this example before in other discussions on Raw capture with DSLR's but it explains the fluoresce effect I'm talking about I had to edit in order to emulate the effect.

Thinking back to the art gallery curator I wonder if he could've achieved the same effect shooting the paintings under the halogen instead of the daylight CFL. Of course Delta E number measuring wouldn't have helped because the edits were all based on perception, not exactly measured spectra
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digitaldog

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I do think digital might be too good at color reproduction that raise unrealistic expectations for reproduction on inkjet prints for some "Southwest Art" style artists who want to reproduce the brilliant oranges, yellows and tans in their acrylic paintings viewed under halogen lights. It's sort of a fluoresce effect that I had to assume some inkjet printed inks can't reproduce.
With proper colorimetry and deltaE reporting, no need to assume; provide some measurement data of the acrylic painting, in areas from these English words to describe a sensation (brilliant oranges, yellows and tans), a good ICC profile from any ink jet printer, some here can tell you with absolute certainty if they can or cannot be reproduced on that printer!  :-*
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Iliah

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Yes, digital is better. In 80s it was absolutely impossible to reproduce a painting accurately enough, a print compared to the original was visibly very different, even with no limits to budget (like when working for the Kremlin museums). But the criteria in museums were also relaxed. Now to get the work accepted I need to pass "deltaE" test. The bar is now much higher, and "just digital capture" doesn't cut it.
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Tim Lookingbill

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Yes, digital is better. In 80s it was absolutely impossible to reproduce a painting accurately enough, a print compared to the original was visibly very different, even with no limits to budget (like when working for the Kremlin museums). But the criteria in museums were also relaxed. Now to get the work accepted I need to pass "deltaE" test. The bar is now much higher, and "just digital capture" doesn't cut it.

Iliah, do you ever get comments or criticisms about the print reproduction of paintings not looking eye popping vibrant when viewed under the same light as the original that makes the original look this way?

The Soraa 5000K Vivid spot LED I lit the Frenches Mustard bottle and shot Raw with my DSLR I can't visually duplicate accurately with edits in ACR even using a daylight DNG profile. An Xrite CC chart is no problem.

I probably should try to make a custom camera profile and see if that makes a difference. The Frenches Mustard bottle looks very vivid under the Soraa light and no ACR saturation slider of any kind can make it match. Of course it also could be my sRGB gamut display that's the limiter.
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digitaldog

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I probably should try to make a custom camera profile and see if that makes a difference.
Indeed!
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Jack Hogan

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The Frenches Mustard bottle looks very vivid under the Soraa light and no ACR saturation slider of any kind can make it match. Of course it also could be my sRGB gamut display that's the limiter.

Yes, many saturated yellows even in well known studio scenes are typically way out of gamut (e.g. out of Adobe RGB).

Jack
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ErikKaffehr

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Hi Jim,

What I might conclude from Jack's and your work is that there may be a lot of look to raw processing profiles. It may seem that a simple compromise matrix conversion may produce quite accurate colour, but it may be that colour profiles shift colours a bit for pleasantness giving up on accuracy?

What is your take?

Best regards
Erik

I'm not knocking the talents of the brilliant chemical and industrial engineers at Kodak, Agfa, Fuji, and many other companies. It's just that it is really hard to produce a film/processing -- in the case of 'chromes -- and film/processing/paper/processing -- in the case of color negative films and papers -- system that produces accurate color. At SPIE meetings Ed Giorgianni, a Kodak engineer of some repute, used to give seminars on the details of the color processing of film-based systems. I would walk out shaking my head, amazed that film did as well as it did, considering all the really tough chemical problems involved.

I once did an experiment where I took 25 different 'chrome emulsions (this was in the 90s, when there were lots to choose from), shot a Macbeth chart, and read all the resultant patches with a spectrophotometer. The average CIEL*a*b* delta-Es were in double digits. By the way, the great thing about doing that experiment was smelling film canisters right after I opened them. I loved that smell, and miss it in the digital age.

The engineers working on film systems weren't dummies. They knew they couldn't make it accurate. There was a body of opinion that stated that you didn't want it accurate even if you could do it. So they came up with many clever and artful inaccuracies that we call the film look. But it's not one look, it's a bunch of looks, and none of them are very accurate. Now we have digital systems, and we have less constrictions on what we can do. It's still impossible to build practical systems for color photography with perfect accuracy, but what we have now is much better than with film.

Jim
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Alexey.Danilchenko

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Hi Jim,

What I might conclude from Jack's and your work is that there may be a lot of look to raw processing profiles. It may seem that a simple compromise matrix conversion may produce quite accurate colour, but it may be that colour profiles shift colours a bit for pleasantness giving up on accuracy?

What is your take?


Kodak in the old days when they did produce DSLR cameras and PhotoDesk, solved it in the similar way to RPP - raw conversion profile provides accurate colour and on top of that a "look" profile can be applied when generating the output conversion (applied as one of the last conversion steps if I recall correctly). That separates pleasant and inaccurate looks from profiling the camera and supposedly make it easier to get more consistent results.
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Jim Kasson

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Hi Jim,

What I might conclude from Jack's and your work is that there may be a lot of look to raw processing profiles. It may seem that a simple compromise matrix conversion may produce quite accurate colour, but it may be that colour profiles shift colours a bit for pleasantness giving up on accuracy?

What is your take?

I'll speak to the Adobe camera profiles, since I have more experience with them than with, say, C1. They tend to introduce nonlinearities in the tone curve that impact accuracy but increase midtone contrast and flatten near the white and black points. That adversely affects color accuracy and is undoubtedly deliberate. In addition, Caucasian flesh tones are biased away from green. I'm pretty sure that is deliberate, too.

A year or so ago, Jack and I did a lot of work over on DPR on compromise matrix selection and its effect on accuracy with various cameras and found no camera that could produce 1 delta-E errors across the whole Macbeth chart (which is a very small sample space). So I don't think that you can get great accuracy with commercial cameras and compromise matrices. With LUTs, it should be possible to nail all 24 Macbeth samples, but at the expense of colors not in the training set.

Jim

Iliah

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> do you ever get comments or criticisms about the print reproduction of paintings not looking eye popping vibrant when viewed under the same light as the original that makes the original look this way?

The lights in my case are mostly of SoLux type or natural daylight, so no such problem. Comparing the look of the original under different lights it is easy to see it changes. Monet's painting of Houses of Parliament at Sunset looks rather acidy under FL lights.

> Soraa 5000K Vivid spot LED

In no particular order:
- "bumpy" light spectrums tend to oversaturate certain colours;
- colour transforms, especially LUT-based, tend to reproduce targets that were used to create those transforms in the first place better than arbitrary colours, particularly the colours that are out of the target gamut (another reason to switch to spectral characterization and profiling);
- sRGB may be limiting.
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