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Author Topic: DCamProf - a new camera profiling tool  (Read 720216 times)

scyth

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Re: DCamProf - a new camera profiling tool
« Reply #1480 on: February 27, 2017, 06:03:02 pm »

Actually we might have a chat somewhere in Russian

wow camera forum has the original topic
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daicehawk

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Re: DCamProf - a new camera profiling tool
« Reply #1481 on: February 27, 2017, 06:36:01 pm »

wow camera forum has the original topic
Yes, I`ve read that one too.
But talking Anders into making a GUI-based tool for matrix creating-tweaking with some freedom regarding exposure and preview tone curve seems sweet.
 :D
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Alexey.Danilchenko

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Re: DCamProf - a new camera profiling tool
« Reply #1482 on: February 28, 2017, 04:08:22 am »

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 :-)
I cannot say for modern cameras but their latest incarnation of profiles rebuilt for older ones have actually been quite inconsistent and worsened in quite a few cases (older Nikons and Kodaks from my experience). Better results could be obtained by reverting to older ACR versions of those (in ACR calibration tab - thankfully it is still possible).
« Last Edit: February 28, 2017, 11:54:49 am by Alexey.Danilchenko »
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Alexey.Danilchenko

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Re: DCamProf - a new camera profiling tool
« Reply #1483 on: February 28, 2017, 04:14:38 am »

how is your monochromator/integrating sphere device doing, you did not post anything about it for a long time...
It is at the finishing stages of v2 of that. The manual version that I posted here was v0 ;)

I spent last year and a half (with lots of help and guidance from Iliah) assembling controller boards for fully automated setup with real time light specta measurement (concurrent with the shots taken). The setup is now assembled and partially debugged (firmwares are written for several Hamamatsu micro spectrometers) and the overall controlling software (home grown QT UI) is slowly progressing.

It will hopefully be ready and opensourced before summer.
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Alexey.Danilchenko

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Re: DCamProf - a new camera profiling tool
« Reply #1484 on: February 28, 2017, 04:21:36 am »

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.
In the days of film they involved people with art background rather than photographers from what I understand
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ErikKaffehr

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Re: DCamProf - a new camera profiling tool
« Reply #1485 on: February 28, 2017, 04:20:02 pm »

Hi,

My feeling is that vendors want to surround colour handling with mystery. In the real world, I would guess that there is a bit more science and a bit less of mystery…

Best regards
Erik

In the days of film they involved people with art background rather than photographers from what I understand
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #1486 on: March 01, 2017, 03:30:05 am »

I've been working lately with alternative tone operators. The "neutral" one is the DCamProf signature tone operator and will continue to be so, but I cannot deny that there are users that like the look an RGB curve (S-curve applied on R, G and B channels separately) provides. In addition to pure RGB and Adobes ACR (which works the same as an RGB curve, but with HSV-Hue kept constant) which by raising them to status of tone operator can be combined with gamut compression and look operators and be used in both ICC and DCP, I'm adding a variant called "RGB-Luminance".

It works according to a technique often used in RawTherapee where you have the possibility to manipulate two tonecurves. You then split your contrast into two curves, and apply one tone operator on one of the curves and another on the other. This way you can add saturation and hue control to an RGB curve by combining it with a Luminance curve for he shadow dip. Interestingly it seems this is the same type of technique C1 has in their profiles. By separating out the shadow dip you get a smoother flatter curve used by RGB which reduces its hue shift issues, and you also reduce the oversaturation issues, while keeping some of the subjectively attractive features of and RGB curve. The hue shift is good in some cases as the "hue spreading" means that you make colors more separated than they otherwise would be. At some point I may look into this a bit more also for the neutral tone operator, as I've seen in rendering of woods that its hue accuracy may compress the tones a bit too much, and one may need to make a tradeoff between perceptual hue accuracy and perceptual contrast/separation accuracy, eg spread the hues a bit to gain more separation.

DCamProf uses ProPhoto primaries for the curves, same as DCP/Adobe. This is an oversized colorspace but works well when the curve doesn't cause hue shifts, like Adobes curve or DCamProf's own neutral operator. However with an RGB curve if you apply that with Prophoto primaries you get issues especially that blues have a tendency to turn purple. I've scratched my head a good while over that, and I still can't provide an exact intuitive explanation what properties in the Prophoto that causes this, but on a high level I guess you can say that the extreme "virtual blue" primary (the coordinate is outside human locus) makes the balance between reds and blue a bit unstable, so the curves get an exaggerated effect and thus the hue shift is enlarged.

In short, for an RGB curve, Prophoto is not a good color space to apply it in. What I've done is to add a special "curve color space", which has the red and green primary at its original xy coordinates but I've moved in the blue to the locus. I need an as large color space as possible otherwise the curves won't render high saturation colors properly (as it won't reach them). With the rebalanced modified prophoto the red/blue balance is alright again and the hue-shift problem is gone, or rather, is back to what's normal for an RGB curve. I get a new problem to handle though, that colors may be outside the gamut of this slightly smaller color space. I could just clip them, but that would kill some tonality. Instead I make an auto-extension of the curves below 0.0 and above 1.0. The effect of this is a slight gamut compressing effect of (extreme saturation) reds. I was puzzled at first that when moving the blue primary it was the red channel that was affected, but that is because although the red primary is at the same xy coordinate it's brightness is reduced to balance out with the new blue primary to keep the whitepoint where it should be (D50).

About the curve color space, it's also something that has obviously been thought about in C1 which use a plain RGB curve for the user-selectable curve and it's important for them to minimize hue shifts. I'm not sure if they use the same color space for all cameras, I would rather guess that it varies a little between model to model. In any case it's a large color space, but smaller than ProPhoto, as it seems you can't make a space of that size and keep sane balance between the primaries. Other techniques they use to minimize hue shift is to use the split curve approach (the main shadow dip is in the ICC LUT as a luminance-like curve), gamut-compression to minimize/avoid unstable high saturation colors, and their general warmup of colors (adding in green) does stabilize things a bit. DCamProf profiles are not fully as stable as I've chosen other tradeoffs, preferring more accurate hues and have a bit less aggressive gamut compression.

Adobe on the other hand specifies in the DNG specification that the profile-embedded tone-curve must be applied with Prophoto primaries, which would be really bad if the curve was an RGB curve. The DNG spec doesn't actually specify curve type, but the defacto standard via their own software and their published SDK source code is their own type of Hue-corrected RGB curve and you then don't have the hue shift problem anyway.
« Last Edit: March 01, 2017, 03:51:17 am by torger »
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #1487 on: March 01, 2017, 04:09:33 am »

And here's an example crop, using Bart's image of flowers.

The "original" is actually not original but using the hue-preserving ACR tone curve, to have the similar brightness/saturation to make it easier to compare.

As you can see in the prophoto color space the RGB curve makes a clear hue shift to purple, even if we in this case have removed the shadow dip of the curve (reducing hue shift issues). The modified color space has much less hue shift. It's not zero though, and it shouldn't be as slighter hue shift contributes to the look of this curve type that some like. Its strong aspects are artificial hue separation, that some mistake for being more "accurate", and extremely robust and smooth transition into clipping (great for sunsets, high key portraits etc). For the record the neutral tone reproduction operator has borrowed some clipping behavior from the RGB curve, but not the hue spreading part (so far at least)...

The question "what is the optimal color space to apply a camera profile RGB tone curve?" probably doesn't have a straight answer. If someone think it has, I'd love to hear the discussion. Something "big and balanced", but the exact placement of primaries is not too important is my conclusion so far.
« Last Edit: March 01, 2017, 05:54:54 am by torger »
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delfalex

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Re: DCamProf - a new camera profiling tool
« Reply #1488 on: March 01, 2017, 04:46:05 pm »

The question "what is the optimal color space to apply a camera profile RGB tone curve?" probably doesn't have a straight answer.

Just a thought; When I've been capturing and profiling large color gamut subject matter I've often exported into Joseph Holmes's Dcam 5 or 4 profile for a workspace profile as their chroma variants allow for +/- perceptual colour scaling before final output profiling without messing with tone curve.

Alex

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jrp

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Re: DCamProf - a new camera profiling tool
« Reply #1489 on: March 01, 2017, 05:32:38 pm »

@torger I'm intrigued as to how you are going to design a GUI interface to wrangle all this tractably. ;D
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Alexey.Danilchenko

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Re: DCamProf - a new camera profiling tool
« Reply #1490 on: March 01, 2017, 06:40:20 pm »

The question "what is the optimal color space to apply a camera profile RGB tone curve?" probably doesn't have a straight answer. If someone think it has, I'd love to hear the discussion. Something "big and balanced", but the exact placement of primaries is not too important is my conclusion so far.
Does it have to be RGB? Could you not use Bruce Lindbloom Up Lab?
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #1491 on: March 02, 2017, 03:15:20 am »

Does it have to be RGB? Could you not use Bruce Lindbloom Up Lab?

It has to be RGB when you apply an "RGB curve", that is apply the same contrast curve separately on the R, G and B channels.

That "tone operator" has special look properties. It shifts saturated hues as it won't scale R G and B with the same amount. For example if you have R at 60%, green at 40% and blue at 80% before the S-curve, you will get a lower G value, a higher R value and a somewhat higher B value, a new channel mix which results in a more purple hue than the original. This effect can be exaggerated depending on how the colorspace is configured, as demonstrated in the crops above.

Hue shifts is not the big thing though, what it also does is that it separates the channels more, ie introduces a saturation increase. As we know in human visual perception contrast and saturation is connected, so if you increase contrast also saturation must be increased otherwise the result looks desaturated. That is the super-simple RGB curve does the basics of what any tone operator should do, and in the early days of digital photo editing RGB curve was the thing so it's a look we've got used to. It also have the nice property of super-robust clipping as it rolls off each channel separately. It does mean that bright reds become orange before clipping etc, but it becomes a really smooth transition.

An RGB curve does over-saturate things though, but as many prefer an over-saturated look it's not always seen as a problem. However by combining it with a luminance curve for the shadow dip you can soften the hue shift and over-saturation effects and get a more neutral curve.

When Adobe made the DCP they came up with their own RGB curve variant. The basically do the same thing regarding saturation increase, but correct the HSV-Hue so it stays the same, ie no hue shift (within the limits of the perceptual accuracy of HSV-Hue which is pretty good but not 100% perfect). I'm guessing a bit here but it seems their early attempts of profiles is simply to make a colorimetric base profile shooting some target and slapping on this curve. It makes an okay profile with no/little hue shift problems, but it's certainly not a full take on how to render color. That ACR curve results in grayish blue skies for example, as mathematically keeping the HSV-Hue correct only allows for strong desaturation to clipping. A pure RGB curve will instead twist the hue towards cyan of those skies and keep more saturation.

UP Lab, similar to Lab2000HL, is a good color space for gamut compression as you can scale chroma (saturation) without shifting hues or changing lightness. CIECAM02 JCh is quite good at that too. However applying a curve in that space it would mean to apply it to the L channel, the lightness channel. This works with the same principle as a "luminance curve" that is the end result is that you scale R G and B with an equal amount, which means no hue shift and no saturation change. This is a different tone operator than an RGB curve, with different properties. If you don't want hue shift, you get that. It has a problem though, and that is that it doesn't modify saturation. Intuitively that might seem as a good thing, but as human color perception has contrast and saturation connected increased contrast with kept saturation with perceptually be perceived as increased contrast with reduced saturation.

Unfortunately it's not as easy to just add some saturation to the luminance curve and you're fine, as the perception is not really linear. This is what all the work put into DCamProf's neutral tone reproduction operator is about.

If you ask me one of the few simple tone operators that has decent performance and look is the RGB-Luminance combination variant. I'm sure there are fans of the RGB and ACR curves too though.
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #1492 on: March 02, 2017, 03:46:04 am »


Just a thought; When I've been capturing and profiling large color gamut subject matter I've often exported into Joseph Holmes's Dcam 5 or 4 profile for a workspace profile as their chroma variants allow for +/- perceptual colour scaling before final output profiling without messing with tone curve.

Alex

In theory you could have a linear output from camera, reduce to your desired output space (gamut compression etc), and then apply the tone curve in the final output space. It's probably a good approach, but not for "regular Joe User". A general-purpose profile must be designed to work as raw converters expect them to work, and they expect that the curve is applied directly on camera output, that is before we know what the user's output space will be. It's the same with gamut compression, we have to apply that before we know the output space. It's surely non-optimal, but the way raw converters are designed today it's the task of the camera profile. If you're an advanced user and have the tools you can change the workflow though.

It would be problematic to apply it on the output space too though, as it would slightly change the look depending on output space, while if you apply it on a fixed space and then use ordinary gamut mapping/clipping to the output space the look is more uniform with different output spaces.

Why not apply it directly on the camera's "raw" color space? I haven't actually tested that yet, but I think it's a bad idea as depending on how the camera raw to rgb matrix becomes (decided by the target matching) I guess we can get the same "un-balanced" issue as with the ProPhoto, and some cameras would have issues with hue shift and others not etc, so it's probably better to have a fixed space, or at least some space with certain fixed properties. I haven't fully figured out what primary positions that work or not regarding hue shifts, more than I have spaces that work and those that don't.
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #1493 on: March 02, 2017, 04:38:36 pm »

Here's a few examples of how much (or little) difference tone operators do.

I've used the Hasselblad X1D Raw Sample http://www.hasselblad.com/inspiration/gallery/sample-image-downloads by Chris Crooze as a demo. I don't really have a colorchecker shot from an X1D so I had to use some less-than-optimal-lit H5D-50c CC24 to make a profile. So I can't really guarantee the accuracy of the profile, but that's anyhow not the point: we can pretend that the middle shot represents the colorimetric truth. It's linear curve -- that is no tone operator active, and pushed one stop to be easier to compare to the others.

The others all have the exact same contrast curve. From left to right:
ACR - Adobe Camera Raw's HSV-Hue-corrected RGB curve
NTRO - DCamProf's neutral tone reproduction operator
linear - the linear reference
RGB-Lum - RGB curve with luminance for the shadow dip
RGB - pure RGB curve.

Actually side-by-side comparison is not that good, when evaluating for real I never do that. A/B swapping with a few seconds adaptation is the the way to do it. Here side by side the eye don't really get a chance to adapt properly so it sees "the mean" of the all, so the NTRO and RGB-Lum may look a bit under-saturated, while more on target with A/B swap. The difference are also much easier seen with A/B swaps.

The intention of the NTRO is to show perceptually the same image as linear, contrast being the only difference. I'm pleased with the performance. Should one point out some error I think the lipstick is probably a bit too dark.

RGB/RGB-Lum shifts skintone hue towards yellow, and clearly desaturates highlights. The cheeks on the portrait may be seen as more "lively" due to the variations in color-shift (more neutral in darker areas, and more shifted and desaturated in lighter) which is lacking in ACR and NTRO. I was a bit surprised of the quite large color shift, and actually checked if C1 has the same color shift in portraits -- and it has. But most likely they have pre-modified the hue of the linear profile so it ends up where they want it when the RGB curve is applied (C1 shows yellow skin anyway, but I think it's a design choice).

While color-shift introduces more "color separation" in some aspects of the skin, it instead reduces color separation in the yellow rose, as the weakly orange tones in the center of the petals are shifted towards yellow, the same tone as the sides of the petals, while this hue is kept in ACR and NTRO.
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delfalex

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Re: DCamProf - a new camera profiling tool
« Reply #1494 on: March 02, 2017, 05:37:32 pm »

For my use the NTRO curve would be a great help in speeding things up in that as I'm often having to start from a more linear base upon which I am adding a luminance curve and then finally chroma. Is the
NTRO curve tweakable?

Will this be available in the GUI version of the program?

Alex


Sent from my iPhone using Tapatalk
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Tim Lookingbill

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Re: DCamProf - a new camera profiling tool
« Reply #1495 on: March 02, 2017, 05:45:25 pm »

Don't know why all your versions are much lighter than what I got in CS5 with embedded profile. I downloaded the file and opened in ACR 6.7 and it didn't let me choose different profiles like other Raw files I've downloaded from other camera manufacturer sites that are compatible with CS5.

I got the model's forehead to read (L*68 a 20, b 20) switching to Linear curve, +1.0 Exposure, +10 Fill, +3 Black, +10 Brightness, +40 Contrast, +10 Clarity, -5 Saturation. Decent results.

Maybe there's a display calibration discrepancy where everyone's gamma curve is slightly more or less contrasty. Not sure. This is why I've attached a screengrab of my ACR edits from Photoshop preview. 
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #1496 on: March 03, 2017, 02:39:33 am »

For my use the NTRO curve would be a great help in speeding things up in that as I'm often having to start from a more linear base upon which I am adding a luminance curve and then finally chroma. Is the
NTRO curve tweakable?

Will this be available in the GUI version of the program?

I was using the GUI to make the examples above. Not sure how I'm going to do with the RGB-Lum yet. Designing a profile in DCamProf can be seen as a multi-stage serial process, 1) make a colorimetric base profile, with possible "subjective" adjustments regarding the unavoidable errors, eg prefer having skintones a little bit too warm rather than too cool etc, 2) choose gamut compression (possibly with tuned parameters), 3) apply a curve via a tone operator, normally the NTRO, possible with tuned parameters 4) apply subjective color adjustments.

That is the major subjective part is left until the last stage, and to make this logical it requires that the tone operator doesn't distort too much. If you however use something like the RGB-Lum it's probably wiser to make subjective adjustments *before* the curve is applied. The reason being that it's difficult to cancel out the color shifts cause by RGB-Lum afterwards, so it's better "pre-distort" colors so they end up where you want them. While you can do this with DCamProf and the GUI it's not really designed for that order of workflow so it's a bit awkward.

So I'm thinking of making it possible to blend in some RGB-Lum elements in the NTRO as a part of tuning that or some other way. I'll probably keep in the RGB/ACR/RGB-Lum/RGB operators as plain choices just for reference anyway (good to compare to, to get a feeling of the effect of tone operators), but currently the only way to make a "high end" profile in a smooth and easy way is to use the NTRO.

I'll think some more about it and make some more experiments and see where it ends up.

The tone curve is tunable, I've put quite some effort into the curve editor so it should be effective in fine-tuning a tone-curve. The NTRO has a bunch of parameters in addition to the tone curve, all are tunable via JSON configuration like in command line but in the GUI the only tunable factor I've exposed is the overall saturation factor, which normally is left unchanged at its automatic value. I think this will be enough for the first version.
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #1497 on: March 03, 2017, 02:57:28 am »

Don't know why all your versions are much lighter than what I got in CS5 with embedded profile. I downloaded the file and opened in ACR 6.7 and it didn't let me choose different profiles like other Raw files I've downloaded from other camera manufacturer sites that are compatible with CS5.

I got the model's forehead to read (L*68 a 20, b 20) switching to Linear curve, +1.0 Exposure, +10 Fill, +3 Black, +10 Brightness, +40 Contrast, +10 Clarity, -5 Saturation. Decent results.

Maybe there's a display calibration discrepancy where everyone's gamma curve is slightly more or less contrasty. Not sure. This is why I've attached a screengrab of my ACR edits from Photoshop preview.

When it comes to Hasselblad cameras and ACR there is no profiles provided, that's why you can't choose different profiles. I don't know if this is because they have integrated Hassy's native color model, or if they only do the basic embedded color matrix. It's a mystery on its own as Hasselblad has claimed excellent Lightroom compatibility etc, but if that doesn't come with high end color profiles it wouldn't be true.

The difference in brightness is because I've pushed the exposure, forgot to mention that, and the reason for that is because I think the original image is a bit under-exposed. With portraits and skintones profiles are generally (indirectly) optimized to provide the best results at a certain exposure. Much of the tunings are non-linear and as such won't work if the face isn't put at the expected range of the tone curve. The differences between different profiles also turn out more if the portrait is somewhat high key, as the rendering of skintone highlights is very telling.

More "accurate" profiles often show problems with skintone highlights, they simply keep too much of the original hue so the result looks a bit flat and muddy, while classic RGB-style operators will shift and desaturate a bit making the skin looking more fresh. Some of this has already been taken into account with the NTRO, which in its first incarnations had some of those issues. I may even integrate more of this effect, it's a work in progress.

After a contrast curve has been applied color value readings doesn't mean much. Basically the only thing you can trust is hue (as our hue perception is approximately constant with contrast), but then you need to take hue readings in a color space which has straight hue lines, UP-Lab, Lab2000HL, CIECAM02 JCh, and actually RGB-HSV is not too bad except perhaps in the blue range. Our perception of saturation changes with contrast so saturation readings become meaningless, and lightness is part of the contrast of course. The rolloff range into the white-point is also longer than one may think, the desaturation process related to that starts quite early. So evaluating result in the end is about using our eyes.
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #1498 on: March 03, 2017, 03:33:03 am »

Here's an image to more clearly point out what I mean with what one could see as "livelier" skin-tones and "desirable hue shifts". I'm not saying that it's necessarily better, I personally prefer the NTRO rendering, but there may/might be elements to borrow from RGB-Lum.

I've marked the left cheek with a circle and split it in two. It looks like a "forbidden sign" I know, but it's entirely unintentional :-). The lower-left half the RGB-Lum is quite hue accurate, while in the brighter upper-right half there's some hue shift and stronger desaturation effect, while NTRO maintains correct hue better. In other words the RGB-Lum introduces some "artificial color separation" and gives a slightly more contrasty look despite having the same tone curve. (They're not ideally comparable as the global saturation of the RGB-Lum is a little bit lower than NTRO).
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Tim Lookingbill

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Re: DCamProf - a new camera profiling tool
« Reply #1499 on: March 03, 2017, 04:04:36 am »

So evaluating result in the end is about using our eyes.

I added one full stop exposure in ACR on that sample as well but I could've gone farther but stopped to avoid blowing out the spectral highlights in the buttons on the dress which you've cropped out of your sample.

All I'm concerned about by going through the trouble of making a custom profile is maintaining consistency when increasing exposure or brightening an image but at the same time preserve modeling detail in such surfaces as fabric and non-spectral skin highlights in the area of 200RGB. Of course the only way I've been able to achieve this in ACR is by using PV2010's linear styled function engineered in its Exposure slider after zeroing out all other sliders in the Basic Panel and adjusting for a neutral or slightly off white white balance.

Your attempt at building DcamProf profiles to control skin highlight hues nearing max brightness seems to leave out or avoid mitigating against the hue shifts from spectral fluorescing of foundation makeup which this sample image has at near pancake levels making this sample image not ideal IMO for testing the effects of various contrast curves on hue/saturation shifts.
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