singers indoor, high iso: how to remove nasty blue

Processing Play Raw
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@sovereign: thanks Matteo for pointing that out – I have indeed totally forgot about the other channels!

I still like your version the best so I’ll ask again: what is the process that you used to come up with those parameters in channel mixer? I can’t believe it’s trial and error, there must be thought process behind…

@ggbutcher Your explanation makes sense and I have seen that in fact just by changing the input profile to prophoto rgb the entire image changes quite a bit (I mean the colors); the histogram does change significantly.

I’m now using this profile for this particular image but then – what’s the rationale behind? That when photos are taken in difficult lighting conditions… then one must change the input profile? For what – one that is as wide as possible like prophoto? Is one supposed to change input profiles whenever… something happens? like shooting at night or in clubs?

I realize that I don’t even know what is the question that I should ask!

Finally, I’ll reply to the question I’ve asked @yteaot above about color zone module. With a bit more fiddling I have seen that to draw a square hole one must use the monotonic spline interpolation, alright! Then I have been able to replicate (more or less) what you did. I think this is the easiest tool to use even though I prefer the outcome using the channel mixer as I said earlier.

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That’s why I’m working on the spectral profiles, ‘one profile to rule them all’. Getting camera measurements transformed down to the display gamuts is more suited to a non-continuous function captured in a mechanism like a LUT. If you dissect the Adobe camera profiles, that’s what they’re using.

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Those values may come from Out of gamut colors, matrix, hsv - at least that’s the only post I found them (thanks for posting them here!). They do work remarkably well on this shot. I’ve added a bit of Lut3D and came up with this:

20191201_NIK1145
20191201_NIK11451920×1282 1.12 MB

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Ciao @aadm, what I did is a (very) creative color grading, and it does not make sense in every situation. In this case I replaced the blue channel with green (mostly) and red.

You can try the following to achieve in a few simple steps a very basic look that you can further refine:

  1. set the exposure to automatic
  2. activate the channel mixer and drag to zero the blue in the blue channel: the image will assume a yellowish cast because what you are left with are just the red and green channels.
  3. mix the green and red in the blue channel as you find pleasant; try for example 0,965 for green and -0,030 for red; aim for a nice overall color balance.
  4. activate local contrast with default parameters.
  5. apply denoise profiled and hot pixels removal.

Here you are the result:

20191201_NIK1145
20191201_NIK11452048×1368 1.22 MB

As you see, the core steps are really few and simple.
The fine tuning might require some fiddling though …

To answer your original question, I didn’t do any math to set up the channel mixer.
I begun more or less in the way I described and then, touch after touch, I reached the final result.

To adjust the final color with the color balance was a sensible way to refine the result.
To adjust the white balance instead was probably not necessary.

Note: I am using the scene-referred processing style (filmic rgb activated by default).

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20191201_NIK1145-1
20191201_NIK1145-13000×2002 1.66 MB
20191201_NIK1145-1.jpg.out.pp3 (12.8 KB)

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Here’s my shot at it. Very reminiscent of the problems I had with my Hummingbird Play Raw

I wanted to keep the warm stage and the blue back lighting, so I used the channel mixer with a blue parametric mask to tone down and desaturate the blue. Once the blue was better balanced in the picture I used the color balance to bring up overall saturation and contrast.

Nice play raw… thanks! Let me know if you have any questions.

20191201_NIK1145
20191201_NIK11457379×4927 14.1 MB
20191201_NIK1145_01.nef.xmp (26.7 KB)

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Thank you for the link. Yes the @age matrix is a very simple and effective way to tame the blue, keeping all other colors with only a slightly warmer color balance.

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Minimal processing: PhotoFlow for raw and gmic for post. Lighten blues, add contrast and brightness. Sure, more could be done such as chroma reduction, colour correction and image enhancement.

pr20060-afre
pr20060-afre1920×1282 1.78 MB

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@sovereign : Thanks a lot for the walkthrough Matteo! Very informative and always nice to learn something new about how to use a particular module (I normally use channel mixer only for B&W conversions using the presets listed in the manuals for different films).

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@Dave22152 thanks Dave, I’m looking at your parametric mask because I wasnt able to make a good one so it is instructive to see yours.

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I set the parametric mask to Hue and used the +eye dropper to select a blue area. Then I activated the mask view applied the mask blur to spread it out so it’s blurry and uniform across the region. That’s the critical part. Sometimes you have to play with blur, feathering and contrast to get it right.

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After scrutinizing the different results, I think the main problem is to keep the details that are present but hidden in those blue regions and let them appear in the output image.

Looking at the hairs of both singers but mainly of the woman, it seems that more or less some processing cannot reveal those details. The first exemple from @aadm is a clear exemple of the absence of detail in hair (no offense intended!). The transformation of blue in black does’nt always improve the situation if the details remain hidden.

So my conclusion is that the issue is not the presence of the “nasty” blue in itself but mainly in that case the loss of the existing details due to a weakness in the processing pipeline starting perhaps with the choice of a suitable camera profile.

I spoke of defective input profile, sorry if I offended somebody, but english is not my native language. Thanks @ggbutcher for the clarification about camera profiles.

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Actually, they’re all ‘defective’, in that they’re all just approximations of space on the spectral response of the camera. Even the SSF-based profiles I’m currently making are anchored on the 24 colorchecker patches and surely miss characterizing colors I haven’t yet lamented. I’m going to try making a few profiles from other references, like the Munsell set (1600 patches!), see what happens…

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What I did for my entry isn’t so much to make it look impressive but to demonstrate the utility of a good mask. This is the one I used to brighten the blues.

Small size

mask
mask960×641 314 KB

But we can do better after we handle the blue. Notice that the mask covers only a part of the hair; viz. the blue parts. To recover detail, after mitigating the blue, we should modify the mask so that we don’t see any hair detail; i.e. the mask includes all of the hair instead of only the blue strands. (Self-bookmark for future gmic exploration.)

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@Jade_NL: You have a straight line at an angle in contrast equalizer. I don’t find that among the presets. How did you get that?

Also, why do you use tone curve and not rgb curve?

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This is based on the sharpen preset. I used the mix slider to bring the right side down. I now notice that there might be a visualization bug in this mix slider.

I remember also playing with the chroma setting and not liking the results, so I double clicked to reset it. This also resets the mix slider to 1.000 even though the actually setting for the luma tab is +/- 0.600

  • It’s situated above filmic and thus it saves me the hassle of moving yet another module,
  • It has L*a*b options that I use at times,

I only use the rgb curve in combo with the exposure module to anchor my middle grey early in my edit process, but that is a temporary use and it is disabled once I nail the grey point I’m after.

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@Jade_NL
Thanks for the answer, Jacques. I appreciate your help.

To study and learn from what others do I have two installations of dt3.3. One is for editing and one for examining the development of the xmp of interest. For anyone who is interested in trying that, it is important that in settings for the second, examination installation, under storage/xmp, un-check: write sidecar files for each image.

I have been going through your xmp and matching the settings on my own xmp. As I go, I compare the look of the photo images and also the histograms and the module tooltips of settings in the history. I use the waveform histogram. Everything goes well until I set up color balance, although there are some small discrepancies between my tooltips and yours earlier.

The tooltip for white balance for your xmp is:

image
while mine is:

image
I don’t know where the emerald nan setting comes from, therefore I can’t understand the difference. As far as comparing the images and histograms at that point, I can’t see any difference.

Later, for filmic your tooltip is:

image
and mine is:

image
There is a very small difference in white relative exposure, and a bigger one with hardness. Since that is auto-set, there seems to be nothing I can do about it, but the fact that there is a difference would seem to indicate something different about the images. Your tooltip says you are using the 2019 version of the spline generator, although in the filmic settings, color science is set to v4(2020). At any rate, I detect no difference in the graphs, nor in the photo images and histograms.

Coming at last to color balance, at this point obvious differences in the images and histograms appear.

This is your setup:
image
Mine is exactly the same.

Your tooltip and mine to the right of it are:
image image
lift[0] appears to be 1+lift factor, which corresponds to gamma[0] and gain[0].

lift[1] appears to be 1+lift saturation, while lift[3] is 1-lift saturation.

Your gain[1] appears to be 1-gain saturation , while my gain[1] doesn’t seem to correspond to anything.

My gain[3] appears to be 1+gain saturation, whereas your gain[3] doesn’t seem to correspond to anything.

I haven’t been able to decipher lift[2] and gain[2].

Do you, or does anyone, have an explanation for this?

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Too be honest I haven’t put that much time into the latest development version.

I did notice differences between 3.2.1 and (at the time) current master. I asked about it and some of it is explained with this reply from Aurélien Pierre.

I’m assuming for the moment that there are other tweaks and adjustments done to the algorithms that will show (very?) small differences in the end-result when comparing the same settings in 3.2.1 and 3.3.

I opened the above image in 3.2.1 and, after copying both file and xmp to my 3.3 work area also opened it in the latest master: There’s a very slight difference in luminance, visible in the dark(er) parts. Development version 3.3 being just a tad darker.

I have noticed the new tool-tips in the the development version, which is rather nice, but I haven’t looked at the actual numbers and their meaning just yet.

Anyway, that’s all I can say about your findings. Maybe a developer can shed some more light on that.

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There should be no difference in algorithms between 3.2.1 and 3.3. Same parameters should give the same result. Only defaults settings have been touched up. Under the hood, it’s all the same.

lift[0], gamma[0] and gain[0] are the luminance factors. The [1], [2] and [3] are R, G and B factors respectively. Saturation and hues are computed dynamically from/to those RGB params normalized in luminance, they are not used in the actual algo (they are UI only). They are all compensated such that 0 in interface == 1 in params == neutral setting for the parameter (no-operation in the algo).

So if any set of settings/XMP produces different “interpreted” parameters in different versions of dt, this should be reported as a bug.

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I loaded Jacques’ xmp in dt3.2.1 and compared it to 3.3 and found no difference in color picker samples: rgb: 57, 54, 50 for both. Lab had a small difference: 3.3: 22.95, 0.68, 3.05 vs. 3.2.1: 22.96, 0.68, 3.05. I wouldn’t know how to get interpreted values for 3.2.1.