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Author Topic: DCamProf - a new camera profiling tool  (Read 767318 times)

ErikKaffehr

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Re: DCamProf - a new camera profiling tool
« Reply #600 on: June 19, 2015, 05:53:32 am »

Hi,

What about just applying tone curve to the luminance channel?

My take is really that raw conversion should result in a scene referred image and different kind of "looks" could be applied that image. I don't know if this is in conflict with DCP-based processing.

Best regards
Erik

Searched some more on tonecurve stuff, and it's not that easy to find any obvious solution to the problem. In the research world this is called "tone reproduction operator", and they have since 10+ years left the simplistic one global tone curve approach and are more into spatially variable operators, that is what we usually call tonemapping. A profile can't do scene-dependent corrections so we can't use that kind of stuff.

The traditional RGB tone curve is not only about creating a subjective look, but also to fix appearance issues, mainly Stevens and Hunt effects (contrast and colorfulness appears higher in a real bright scene than if reproduced with lower luminance on a screen). Digging down you also have Helmholtz-Kohlrausch effect and Bezold-Brücke hue shift effects. All these effects are scene-dependent of course, but you could say a fixed tone curve roughly matches a sunny day, and it's probably good approach. It will make duller scenes look more contrasty than the real deal but that's probably how people will want to make it look anyway.

The big name raw converters are in any case not designed for scene-dependent appearance modeling, we have this fixed tonecurve to relate to. And then my idea is that I want a tone curve which changes contrast, but colors appears to be of the same hue (and saturation) as before. It's there the current raw converters with their RGB curves fail miserably, making a linear colorimetric profile produce bad colors. But a profile can always compensate to give you any result you'd like, and it's exactly what the big names do (with varying success). My plan is to make it possible to make tone curve compensation with DCamProf profiles as well, but using some good appearance model rather than relying on golden-eye subjective hand-tuning which many commercial raw converters seem to be doing.
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Alexey.Danilchenko

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Re: DCamProf - a new camera profiling tool
« Reply #601 on: June 19, 2015, 06:57:36 am »


The big name raw converters are in any case not designed for scene-dependent appearance modeling, we have this fixed tonecurve to relate to. And then my idea is that I want a tone curve which changes contrast, but colors appears to be of the same hue (and saturation) as before.

Check RPP out
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Bart_van_der_Wolf

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Re: DCamProf - a new camera profiling tool
« Reply #602 on: June 19, 2015, 09:16:57 am »

Check RPP out

Only possible on Mac ...:(

Cheers,
Bart
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #603 on: June 19, 2015, 10:45:59 am »

What about just applying tone curve to the luminance channel?

My take is really that raw conversion should result in a scene referred image and different kind of "looks" could be applied that image. I don't know if this is in conflict with DCP-based processing.

Current raw converters are a bit of a mixture of old film techniques and new color appearance models. White balance or tone curves do not exist in color appearance models like CIECAM02. In color science speak white balance is a simplified chromatic adpatation transform, and an RGB tone curve is an over-simplified tone reproduction operator. Color science is busy with making realistic reproductions, even emulating eyes night vision etc (meaning that you need to know exposure level too), and taking view conditions into account. To make it state-of-the-art is very complex. Documentary video seems to be the natural applications of these types of ultra-realistic reproductions.

The first part of DCP could be said to be scene referred, but the tone curve is certainly output referred. As I want DCamProf to be a profile maker also useful for the big name raw converters I need to adapt to their workflows. Personally I'd surely prefer that a profile only did the scene referred part, and the raw converter took care of all output modeling, but that's not how it works in Lightroom and Capture One for example. They expect a curve to be there, and if the profile is linear scene referred only there are no tools to add contrast to adjust the look without having color shift effects.

In photography we seem to settle at rendering D50 bright sunny scenes fairly realistically in an average viewing condition, and then accept as a bonus the extra "pop" we get when we apply the same tone reproduction and colorfulness on other conditions. I'm fine with that. Problem is that the RGB tone curve is as discussed a very bad tone reproduction operator which don't even make the sunny scenes realistic but makes color pop like crazy, and in some circumstances cause hue shift as well. Bundled profiles are semi-compensated for that, by hand I suppose for more exclusive cameras.

I'm trying to find an automated way to compensate a profile so it can be used with RGB curves without getting crazy results.

Applying contrast to the luminance channel is a good idea, but then the next question is which model of luminance should we use? Using Lab Lightness results in a desaturated look. I'm currently experimenting with using CIECAM02 lightness and that is a better perceptual model than Lab and gives better results. However, as we apply lightness contrast to simulate a brighter outdoor condition (Stevens effect) we still get a desaturated look due to the Hunt effect, to match realistically we need to add some saturation too. It's there I am now. It seems like this problem hasn't really been solved before as those that work with CIECAM02 don't work with traditional "film curves".

A color scientist would just say it can't be done without knowing all scene parameters and viewing condition parameters, but I'm looking into using that sunny D50 scene as a reference, I think if it works for that scene we'll have a suitable "neutral" look that photographers can identify with. The bright outdoor sunny scene is really the only condition that mandates increased contrast and saturation.
« Last Edit: June 19, 2015, 10:49:06 am by torger »
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #604 on: June 19, 2015, 10:48:22 am »

Only possible on Mac ...:(
no, both RPP and Iridient do work in OSX and OSX does work in VmWare (yes, EULA says you can't, but Apple can take a hike) and VmWare does work on PC/Win...
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #605 on: June 19, 2015, 10:54:58 am »

RawTherapee is also a good experimental box for trying out "scene referred" workflows, in RT you have the CIECAM02 mode, where you can enter scene conditions, viewing conditions and all, simulate light dark adaptation and partial chromatic adaptation etc.

You can also apply contrast in Lab, CIECAM02 J or Q, or use their own custom "weighted standard curve" which is a quite good curve when it comes to keeping hue/saturation constant.

As said though we don't want to keep saturation constant as we have the Hunt effect to think about, if we just add contrast the impression is that we reduced saturation even if it was kept constant. We could also argue that hue should not be kept constant either due to the Bezold-Brücke effect, but I think that is overkill. So my current idea is to add contrast and saturation in some sane way and keep hue constant.

I can recommend this link for those interested in those color appearance effects: http://www.handprint.com/HP/WCL/color4.html
« Last Edit: June 19, 2015, 11:05:02 am by torger »
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #606 on: June 19, 2015, 01:09:54 pm »

Small demonstration.

Same profile on all images (a matrix-only profile). First image is with linear curve (this is the reference), the others have the same contrast curve. One is CIECAM02 J lightness only (second image), hue and saturation/chroma constant. The other (third image) is the same, but with a subjective increase in chroma.

If you really just stare at the pure colors and compare you'll probably see that the constant hue/chroma matches the linear the best. If you look at the picture "globally", the constant hue/chroma looks slightly desaturated compared to the original linear curve, and then the one with slightly increased chroma may look more "right".

For reference I've added a 4th image which is a pure RGB curve in sRGB space (which here makes a better result than doing it in ProPhoto space like DNG). With sRGB and this color I don't think the RGB curve pulls it off that much, maybe a little towards yellow (hue shift is worse if done in Prophoto due to clipping). The obvious difference is that it's grossly saturated, way over the top.

It's quite subtle differences we're working with here, so it can be quite hard to compare with the images one below the other, especially since screens vary in color and contrast slightly depending on viewing angle. Downloading and flipping through them in an image viewer makes it easier.

I'm thinking that DCamProf users will want results similar to image 3, that is contrast in lightness, but with some added saturation.
« Last Edit: June 19, 2015, 01:38:05 pm by torger »
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #607 on: June 19, 2015, 01:34:40 pm »

For the sake of completeness, here's one with the RGB curve applied in Prophoto space, here without gamut mapping which makes the hue shift more evident.
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #608 on: June 19, 2015, 03:48:37 pm »

I think it's quite clear from the little demonstration that you cannot see the profile and curve separately. That's why I'm skeptical about the practice I see many do in Lightroom and Capture One of changing to linear curve to get "more accurate color" out of the bundled profiles. Most likely the bundled profiles are designed for the default curves, and if they are they have changed the color to a big extent to work with that RGB curve, meaning that color may very well become less accurate when used with a linear curve.

I see on the forums that curves are by many seen as some minor thing you add on top to get a little contrast, but it makes a big difference in global color appearance, and for some colors hue shift is quite noticable. Striving for utmost precision in targets and measurements when making an own profile is all thrown out the window if we add a standard curve on top and think we still have accurate color.

We can always fall back on the argument that accurate color is not important, as we will subjectively tune the look to something that pops anyway, and I have no problem with that view. However, the vision I have with DCamProf is to provide to photographers that want it a neutral starting point to add their artistic intent on top, rather than getting a random starting point.

For my local runners club I shoot running competitions from time to time, and it's with bundled profiles impossible to get those supersaturated sports apparel look the same hue as in real life, which I think is remarkable that we can't do in 2015. And although I can agree that maybe it's not that important, it feels silly that my expensive gear and software can't do it. Although I add a subtle subjective look to my images, having the wrong hue on peoples clothing is not a part of my artistic intent, it just becomes like that because profiles and raw converter is not up to it. The film legacy have shaped raw converter design into making it more difficult to get realistic color than it had to be, and I'd say the lack of a proper tone reproduction operator is 95% of the problem.

If we want to do reproduction photography we're fine though, because in that case we won't be using a curve and then any raw converter with a colorimetric profile will make accurate color.
« Last Edit: June 19, 2015, 03:51:59 pm by torger »
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Alexey.Danilchenko

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Re: DCamProf - a new camera profiling tool
« Reply #609 on: June 19, 2015, 05:46:50 pm »

Only possible on Mac ...:(

And your point here being? I pointed to RPP because it is one of the few converters that does not use RGB of any kind as its internal working space - it uses UPLab. It is quite possible that tonal curve is applied to the L channel there (Iliah can confirm/deny this as I am not entirely sure).
« Last Edit: June 20, 2015, 05:16:47 am by Alexey.Danilchenko »
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Alexey.Danilchenko

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Re: DCamProf - a new camera profiling tool
« Reply #610 on: June 20, 2015, 05:20:46 am »

I think it's quite clear from the little demonstration that you cannot see the profile and curve separately. That's why I'm skeptical about the practice I see many do in Lightroom and Capture One of changing to linear curve to get "more accurate color" out of the bundled profiles.
The approach is still perfectly possible. Matrix only profile + raw development adjustments in raw converter + assigning LUT colour correction profile in Photoshop to bring colour to accurate values. Having said that it is not that easily achievable in LR.
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Bart_van_der_Wolf

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Re: DCamProf - a new camera profiling tool
« Reply #611 on: June 20, 2015, 05:42:39 am »

And your point here being?

Hi Alexey,

The point being that I'd love to try/use RPP (as would undoubtedly many others), but without creating a MAC OS environment or having a MAC, Windows users cannot use it. So suggestions that can potentially solve issues, and that only work on a 'limited' number of setups are partial solutions at best.

One of the DCamProf benefits is that it can be (and is) ported to many OS platforms, thanks to Anders' making the source code available for recompilation into complete working binaries.

Quote
I pointed to RPP because it is one of the few converters that does not use RGB of any kind as its internal working space - it uses UPLab. It is quite possible that tonal curve is applied to the L channel there (Iliah can confirm/deny this as I am not entirely sure).

Yes, that may be useful, but I cannot test it on my Windows machines (unless I purchase and invest time in setting up a virtualization environment).

But thanks for the suggestion anyway, maybe Mac OS users can do something with it (or maybe one day there will be an RPP Windows binary?).

Cheers,
Bart
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #612 on: June 20, 2015, 06:22:13 am »

I have not had that good results of applying tone curve in L in Lab, the look becomes to desaturated, but you can of course subjectively add in some saturation.

In the posted experiments above the curve is actually always run through RGB first, but only to check at what luminance it gets at then it's done in CIECAM02 J. I did that so the curve would look the same luminance-wise to be easier to compare with the RGB result.
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Bart_van_der_Wolf

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Re: DCamProf - a new camera profiling tool
« Reply #613 on: June 20, 2015, 07:26:57 am »

I think it's quite clear from the little demonstration that you cannot see the profile and curve separately. That's why I'm skeptical about the practice I see many do in Lightroom and Capture One of changing to linear curve to get "more accurate color" out of the bundled profiles.

Hi Anders,

I do not think that the Linear curve users (I am one of them) in Capture One do it to get "more accurate color", but rather to have better control and rendering over e.g. highlights. With the default (until one changes that) film curve, there is a significant loss of highlight detail compared to less of a 'shoulder' roll-off designed to prevent hard-clipping.

Also, with my Exposed to the Right (ETTR) shots (as verified with Rawdigger, free of important highlights clipping), the default film curve will seemingly clip my (EOS 1Ds3) highlights by close to 1 stop. So I would need to underexpose (with more overall noise as a result) if I wanted to use the Film curve as it is encoded in Capture One.

Therefore, I much prefer using the C1 controls to adjust the tone curve (or even the profile with the ColorEditor>Save as ICC), but starting from a neutral rendering, so I can better see where the real issues are. That choice of curve shape is not because of the color 'accuracy', and C1 has excellent tools for creating pleasing colors, assuming they were not clipped and reasonably good to begin with.

Cheers,
Bart
« Last Edit: June 20, 2015, 08:24:01 am by BartvanderWolf »
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ErikKaffehr

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Re: DCamProf - a new camera profiling tool
« Reply #614 on: June 20, 2015, 07:53:04 am »

Hi,

I made some test in an IT-8 chart and I got better accuracy in terms of Delta E (CIEDE 2000) with the linear than with default curve in C1.

I absolutely agree with Bart's observation that C1 default curve seems to yield overexposed images. I guess this may explain the reason MFDs are said to provide more DR in the highlights, the default processing and the rated ISO makes us underexpose.

Best regards
Erik


Hi Anders,

I do not think that the Linear curve users (I am one of them) in Capture One  do it to get "more accurate color", but rather to have better control and rendering over e.g. highlights. With the default (until one changes that) film curve, here is a significant loss of highlight detail compared to less of a 'shoulder'.

Also, with my Exposed to the Right (ETTR) shots (as verified with Rawdigger, free of important highlights clipping), the default film curve will seemingly clip my (EOS 1Ds3) highlights by close to 1 stop. So I would need to underexpose (with more overall noise as a result) if I wanted to use the Film curve as it is encoded in Capture One.

Therefore, I much prefer using the C1 controls to adjust the tone curve (or even the profile with the ColorEditor>Save as ICC), but starting from a neutral rendering, so I can better see where the real issues are. That choice of curve shape is not because of the color 'accuracy', and C1 has excellent tools for creating pleasing colors (assuming the were not clipped, and reasonably good to begin with).

Cheers,
Bart
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #615 on: June 20, 2015, 09:14:22 am »

If you make delta E comparisons with curve you need to disregard from lightness, as the curve by nature will introduce large errors. Possibly the linear curve would show less incorrect color anyway, as the C1 profiles are created for a look its hard to know without testing. It's hard to test a curved look for accuracy as saturation need to be added for compensation of perceptual effects. Standard delta E tests don't work for testing appearance modeled color.

I'm sure though the profiles are designed to be used with the default curve. As they use an RGB tone curve they must choose to design for a specific, can't maintain color in both.
« Last Edit: June 20, 2015, 09:23:37 am by torger »
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #616 on: June 20, 2015, 09:20:55 am »

Doesn't negative exposure slider settings work in C1 to bring in highlights? Haven't tried recently so I don't know.

I have noted that C1 cuts away quite some highlights per default, it varies depending on camera though
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ErikKaffehr

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Re: DCamProf - a new camera profiling tool
« Reply #617 on: June 20, 2015, 09:46:52 am »

Hi,

I presume you are right on all issues. For me, the liner curve have mostly been a way to get rid of Delta E errors induced by he non linearity of the L-component.

What I think I have seen on the C1-profiles that they are over saturating blues and may be greens, so they actually go out of gamut for say Adobe RGB on the IT-8 target.

What I have seen is very large deviation on blue patches, like Delta E (CIEDE 2000) around 17 that were widely exceeding Adobe RGB gamut, but still looking very good on screen.

:-) Erik :-)



If you make delta E comparisons with curve you need to disregard from lightness, as the curve by nature will introduce large errors. Possibly the linear curve would show less incorrect color anyway, as the C1 profiles are created for a look its hard to know without testing. It's hard to test a curved look for accuracy as saturation need to be added for compensation of perceptual effects. Standard delta E tests don't work for testing appearance modeled color.

I'm sure though the profiles are designed to be used with the default curve. As they use an RGB tone curve they must choose to design for a specific, can't maintain color in both.
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Alexey.Danilchenko

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Re: DCamProf - a new camera profiling tool
« Reply #618 on: June 20, 2015, 09:56:06 am »

The point being that I'd love to try/use RPP (as would undoubtedly many others), but without creating a MAC OS environment or having a MAC, Windows users cannot use it. So suggestions that can potentially solve issues, and that only work on a 'limited' number of setups are partial solutions at best.

Everyone decides what instruments they need - that includes both cameras and equipment to process the images. I was pointing out that the instrument does exist out there - whether you want to make an effort to use of course is up to you. To me it is just a matter of the choice - same as choosing the camera or lens.

Anyway I am not sure it does exactly what Anders is trying to achieve - perhaps Iliah can clarify it.
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #619 on: June 20, 2015, 10:31:56 am »

If you make delta E comparisons with curve you need to disregard from lightness, as the curve by nature will introduce large errors. Possibly the linear curve would show less incorrect color anyway, as the C1 profiles are created for a look its hard to know without testing. It's hard to test a curved look for accuracy as saturation need to be added for compensation of perceptual effects. Standard delta E tests don't work for testing appearance modeled color.

I'm sure though the profiles are designed to be used with the default curve. As they use an RGB tone curve they must choose to design for a specific, can't maintain color in both.

C1 CE edition was supplied by profiles (and curve files) supposedly for reproduction work... both profiles and curves can be used in a regular edition (unfortunately it seems that Lab readouts can't - or at least I did not find a way)
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