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Author Topic: DCamProf - a new camera profiling tool  (Read 719976 times)

torger

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Re: DCamProf - a new camera profiling tool
« Reply #1460 on: February 19, 2017, 08:09:58 am »

I don't believe in matrix-only profiles for general-purpose work due to 1) how do you apply a contrast curve to a matrix-only profile? I don't think RGB curve or Adobe hue-stabilized version is the answer, and a linear curve is really only for repro work 2) raw converters expect the profile to deal with gamut compression, and you can't do that in a matrix.

That said I do believe that a LUT working on the colorimetric level should not make large changes to the matrix, and you can see that in commercial profiles to that they have similar approach. The LUT contributions is mostly about tone reproduction, ie the curve, and gamut compression.

The GUI version of DCamProf will allow manual matrix tuning, but not really by entering numbers manually, but through manually-controlled refinements on the automatically derived base matrix, it's basically a graphical version of the make-profile/-v parameter of the command line program. I've thought about including numbers/sliders though for those that would perfer that type of direct tuning, probably not in the first release though.

DCamProf matrix optimizer is currently limited to make white-point preserving matrices, that is you cannot make a matrix that tints the neutral axis (you can make an ICC profile that does that, but that's about white balance compensation which is another thing). I have so far not seen any reason to change that. DNG profiles actually requires the ForwardMatrix to be white-point-preserving or else Adobe Camera Raw won't accept the profile.

I often do tweak the matrix by hand, "because I can". My favorite modifications is to match skin better and let others color suffer a bit, make sure deep blue is not too dark and is rather turning towards cyan than magenta, and also looking at the reds which I rather have warm than cool. Then the LUT make minor adjustments on top of that. Greens are generally stable as they have strong contribution from all three channels. This is for daylight. For StdA I still need to gain some more experience.

Lightness control is an issue for matrices. Matrices have pretty large lightness errors in general, but I think it's not a big issue as while we can detect lightness errors very easily in an A/B swap, we don't really remember lightness well, or maybe more accurately put, a color slightly light or dark is not seen as unnatural while a hue that is off or under/over-saturation can be quite conspicuous. I think this is because in an image lightness could be the result of the light in the scene, so the eye doesn't really know what's the right level, while (normal) light doesn't cause hues or saturation to change so we react to that even when we have no reference to compare to. So I think lightness should be the least thing to focus at.

To make the matrix "mallable" it should not contain any strong negative factors, which can lead to clipping. One thing I've worked with quite much in DcamProf project is the overly sensitive blue channel (probably for better ISO and tungsten performance) which cause strong blue subtraction in daylight which can cause clip to black for saturated colors. The solution is to sacrifice lightness accuracy and lighten deep blues significantly. Likewise early results suggest that reds must be lighter than natural for an StdA matrix in order to provide stability.
« Last Edit: February 19, 2017, 08:13:23 am by torger »
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Alexey.Danilchenko

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Re: DCamProf - a new camera profiling tool
« Reply #1461 on: February 20, 2017, 04:41:00 am »

I don't believe in matrix-only profiles for general-purpose work
Would not matrix profiles give you something LUT generally could not - smoothness?

Technically speaking a combined approach is possible - apply raw corrections prior to demosaicing, demosaic, apply matrix profile, apply corrections needed at this stage and save (say in UpLAB). Then assign profile with correcting LUTs to work on the image and prepare final output image.

This approach will work with correcting LUTs and look LUTs - Kodak used something of the kind in their camera SDK (if in-camera matrices were used) though with different working space.
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daicehawk

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Re: DCamProf - a new camera profiling tool
« Reply #1462 on: February 20, 2017, 06:18:11 am »

apply raw corrections prior to demosaicing
which ones - some black point offset and such, or any color corrections as well?
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Alexey.Danilchenko

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Re: DCamProf - a new camera profiling tool
« Reply #1463 on: February 20, 2017, 08:07:59 am »

which ones - some black point offset and such, or any color corrections as well?
In the context of profiles discussion - it does not matter.

But if you take RPP for example quite a few: WB, exposure correction, contrast, black levels and raw channels sharpening.
« Last Edit: February 20, 2017, 08:11:01 am by Alexey.Danilchenko »
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #1464 on: February 20, 2017, 02:23:57 pm »

A LUT that makes colorimetric corrections can indeed cause issues with smoothness, or tonality. That's why I think a general-purpose LUT should be close to the matrix result. Scaling lightness is extra risky.

Then you can have a second stage in the LUT that makes gamut compression, and a stage that makes tone operator adjustments, and possible perceptual look adjustments (cooling shadows, warming highlights and such). It's relatively easy to maintain smoothness in such stages, but you can mess up there too of course.

Matrix-only does have some strong merits, especially in technical photography, such as merging HDR and and other applications when linearity is important. Still I don't see any camera manufacturer or big name raw converter maker do matrix-only profiles, and the reason is as said that they want to control the tone operator, gamut compression and have the possibility to add non-linear looks. Sure one can happen to like and prefer matrix profiles, but to the overall photographic community it's a small curiosity.
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longpvo

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Re: DCamProf - a new camera profiling tool
« Reply #1465 on: February 25, 2017, 08:22:53 pm »

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torger

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Re: DCamProf - a new camera profiling tool
« Reply #1466 on: February 27, 2017, 04:56:26 am »

The answer to the question "why are colors so wrong?" is because they're designed to be "wrong". No of the big name raw converters try to make accurate/realistic color, they make pleasing color in the same way Fuji Velvia film or similar, twist colors to make more flattering result. Some have a signature "brand look", and the warm rendering of Capture One I'd say is such a thing. The make colors warm, because their users like it.
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daicehawk

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Re: DCamProf - a new camera profiling tool
« Reply #1467 on: February 27, 2017, 05:36:08 am »

The answer to the question "why are colors so wrong?" is because they're designed to be "wrong". No of the big name raw converters try to make accurate/realistic color, they make pleasing color in the same way Fuji Velvia film or similar, twist colors to make more flattering result. Some have a signature "brand look", and the warm rendering of Capture One I'd say is such a thing. The make colors warm, because their users like it.
I dare to insist that their warm matrices are dictated by need to get the correct hue of the skin tones under daylight of any temperature as well as tungsten. Basically the RAWs wihout input profile look all red-cyan (with skin being red and all kinds of blue gravitating to cyan). The matrix twists that red-cyan colors to have also a yellow-blue axis. The balance of the red-cyan and yellow-blue in terms of correct hue, lightness and saturation makes a good matrix. Strong blue and purple is great but then we have purple pimples and lips, which overweights having strong blue. Also, having both cyan and blue is usually requires that both colors are not saturated and skin tones get pinky-red.
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #1468 on: February 27, 2017, 06:16:31 am »

I dare to insist that their warm matrices are dictated by need to get the correct hue of the skin tones under daylight of any temperature as well as tungsten. Basically the RAWs wihout input profile look all red-cyan (with skin being red and all kinds of blue gravitating to cyan). The matrix twists that red-cyan colors to have also a yellow-blue axis. The balance of the red-cyan and yellow-blue in terms of correct hue, lightness and saturation makes a good matrix. Strong blue and purple is great but then we have purple pimples and lips, which overweights having strong blue. Also, having both cyan and blue is usually requires that both colors are not saturated and skin tones get pinky-red.

How is raw without input file defined in this case? Linear white-balanced raw data direct-mapped to sRGB color space? Raw data can look quite different depending on how you pre-process it.

If this would be the only way to make skin tones correct it's sort of strange that not everyone is making this color warmup, but rather I think C1 is one of the few. Look at the blues and look at the reds.

I have contact with some DCamProf users via email now and then. Most users use my software as they need something that is more accurate/realistic but still not reproduction (ie they need a contrast curve) than bundled profiles can offer. However there's also the users that don't even compare to the real thing, but just compares with other renderings from other software/profiles, and decide by taste what "looks best" -- this is the normal mode of the typical photographer. To a software developer it can be quite frustrating as there's a bunch of different tastes, and you need to figure out what elements that they do like (they usually can't say, only tell if one image looks nicer than the other) and which they don't, and then in the end be the final decider of what gets in there and and what does not.

In the medium format segment I've looked a bit at Leaf, Phase One and Hasselblad all very respected color renditions, all very different even when the hardware is practically the same. None is very accurate. All have gone through the process of making a subjective profile to suit their customers, and probably having some in-house person being the "master decider" on how the final look should be.
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daicehawk

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Re: DCamProf - a new camera profiling tool
« Reply #1469 on: February 27, 2017, 07:04:30 am »

raw in this case mean RT's Neutral profile, demosaiced manually whitebalanced, prophoto as working profile (clipped to monitor space) with some tonal curve (I do not know what curve this is).
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Alexey.Danilchenko

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Re: DCamProf - a new camera profiling tool
« Reply #1470 on: February 27, 2017, 08:43:09 am »

The answer to the question "why are colors so wrong?" is because they're designed to be "wrong". No of the big name raw converters try to make accurate/realistic color, they make pleasing color in the same way Fuji Velvia film or similar, twist colors to make more flattering result.
I seriously doubt they (raw converters) really have that specific intention in their profiles. Firstly films were not just designed by engineers - but profiles and cameras nowadays unfortunately mostly are. And then looking at Adobe profiles for quite a few cameras - the results they provide out of the box are very far from pleasing. For me that was precisely the reason I stuck with older cameras and learning how to get camera SSF and getting into profiling myself.
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Alexey.Danilchenko

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Re: DCamProf - a new camera profiling tool
« Reply #1471 on: February 27, 2017, 08:47:09 am »

raw in this case mean RT's Neutral profile, demosaiced manually whitebalanced, prophoto as working profile (clipped to monitor space) with some tonal curve (I do not know what curve this is).
Why ProPhoto? It may not even be close to get any representative colour. Why not XYZ directly then in this case (it is after all also sort of RGB space).
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #1472 on: February 27, 2017, 09:54:46 am »

I seriously doubt they (raw converters) really have that specific intention in their profiles. Firstly films were not just designed by engineers - but profiles and cameras nowadays unfortunately mostly are. And then looking at Adobe profiles for quite a few cameras - the results they provide out of the box are very far from pleasing. For me that was precisely the reason I stuck with older cameras and learning how to get camera SSF and getting into profiling myself.

I think companies like Phase One has had much more thought put into profile making than Adobe. Phase One makes cameras too. And I'm quite sure they have been involving their photographers when designing profiles. At least that is what they say, also when it comes to their cameras.

One can see when studying old Adobe profiles that profile design has changed over the years quite much, they have become better with time. They too have learnt stuff. Maybe they even have some good profiles today, I don't know as I'm not the kind of guy that buys and tests the latest all the time :-)
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scyth

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Re: DCamProf - a new camera profiling tool
« Reply #1473 on: February 27, 2017, 09:55:06 am »

No of the big name raw converters try to make accurate/realistic color,

P1 at least does supply repro profiles (and fully linear .fcrv curves) for C1 for their backs ...

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scyth

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Re: DCamProf - a new camera profiling tool
« Reply #1474 on: February 27, 2017, 10:00:13 am »

camera SSF

how is your monochromator/integrating sphere device doing, you did not post anything about it for a long time...
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #1475 on: February 27, 2017, 10:13:11 am »

P1 at least does supply repro profiles (and fully linear .fcrv curves) for C1 for their backs ...

Is it bundled in the main version nowadays, or do you need to purchase a "cultural heritage" edition? Anyway the point was that the reason colors are very inaccurate in the general-purpose profiles is that they are designed that way. The linked article above mentions a few technical reasons too, which is probably just right, but the overall reason is -- designed color. Or perhaps lack of design if you look at some early Adobe profiles, if you just slap some random contrast curve on a matrix-calculated-from-a-target you get quite large effects on the colors too.

Here's a "market speak" description of how Hasseblad developed their look, which they've even given a name "Hasselblad Natural Color Solution" http://static.hasselblad.com/2015/02/hncs.pdf doesn't really say much, except that it's a combined effort of both color science and involving photographers and their color perception.
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scyth

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Re: DCamProf - a new camera profiling tool
« Reply #1476 on: February 27, 2017, 10:44:08 am »

Is it bundled in the main version nowadays

they (profiles & curves) were always supplied with a regular C1
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #1477 on: February 27, 2017, 11:00:40 am »

they (profiles & curves) were always supplied with a regular C1

Ahh now I see them, I was playing with P45+ pictures, and the repro profiles didn't start until the IQ series, and not for all backs, at least not in my old version 8 on this computer.
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scyth

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Re: DCamProf - a new camera profiling tool
« Reply #1478 on: February 27, 2017, 11:25:37 am »

Ahh now I see them, I was playing with P45+ pictures, and the repro profiles didn't start until the IQ series, and not for all backs, at least not in my old version 8 on this computer.

well, at least they do for some... and in any case it was nice for P1 to include them with regular distribution
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daicehawk

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Re: DCamProf - a new camera profiling tool
« Reply #1479 on: February 27, 2017, 05:00:29 pm »

Why ProPhoto? It may not even be close to get any representative colour. Why not XYZ directly then in this case (it is after all also sort of RGB space).
Downloaded an XYZ D50 adopted profile from color.org, will report back. Actually we might have a chat somewhere in Russian, your monochromator setup keeps me wondering if it is worth trying and how are resulting profles in terms of color constancy over the tungsten-D65 or so range of the black body SPD light (OK, I know the D is not ABB, still the locuses are close enough).
Edit: Just have found out that RT does not allow to choose an arbitrary color space described in a profile. The ProPhoto seems to be the largest of the available WORKING color spaces in RT and it has worked great so far for visual verifying of target-derived or base-matrix-tweaked profiles.
« Last Edit: February 27, 2017, 05:54:55 pm by daicehawk »
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