Photo post / audio analogy - de-yellow night shot

[iarga]

With the “cat image”, I would do something like this with G’MIC:
First G’MIC>Colors>RGB Tone

[G’MIC] RGB tone: iain_rgb_tone -47.94,-32.13,-48.96,0.51,-3.57,41.31,-6.63,-4.08,4.08,-27.03,-15.3,-2.04,4.59,-8.16,-21.42,0.51,14.79,-9.18,-62.22,9.18,79.56,-30.6,15.3,51,10.71,19.38,27.03,255,255,255,255,255,0

The cat has a magenta tint now.
Therefore I use G’MIC>Colors>HSL Adjustment:

[G’MIC] HSL Adjustment: gcd_hsl 0.916,-0.13,0,207.36,0.079,0,1,1,0

Thereafter a final correction (assumed the cat’s fur and car tire are gray) with G’MIC>Colors>Curves:

[Underexposed (Bill Martz)]

@Soupy
Heh. There were 69 steps in that history list, although once you settled on just channel mixer in step 40, it took only 27 more adjustments to get where you wanted it.

@Jade_NL
Besides using color picker, I have the histogram set for waveform RGB parade. I find both useful for getting the channels equal. However, many times I had them equal and still had blue instead of gray on the cat’s belly.

Soupy didn’t use brightness but still got a well exposed image by the level of RGB he used. I played with brightness, but still didn’t get around the blue belly problem.

I also tried using just color balance, but it took channel mixer to get free of the yellow.

[Underexposed (Bill Martz)]

channel mixer rgb offers the ability to normalize the channels. I have tried that and struggled just as much as without it to get the desired result. If I understand right, using it maintains the gray level. Is it worth it?

[gaaned92]

@Underexposed

didn’t get around the blue belly problem

I don’t understand why you make things complicated. It is just to to add the complementary color

[Soupy (Tim)]

@Underexposed

Heh. There were 69 steps in that history list, although once you settled on just channel mixer in step 40, it took only 27 more adjustments to get where you wanted it.

Sure, but I posted two different versions in this thread. The first version I was playing around with a combination of color balance, channel mixer, and color zones. That was 26 steps in the first xmp, so the second version was more like 40 adjustments - a couple of which are simply resetting and turning off what I did in the first version to start over. As I said, most of the adjustments were trial and error to reach the correct values - I didn’t do it mathematically I was just moving sliders a little this way, a little that. It could be done mathematically, but I am not a mathematician at heart, and it’s not very time consuming to just eyeball it. I knew what I was aiming for and how to get there (r=g=b), but didn’t know exactly which slider (r,g, or b) in each channel would get me the most natural looking result, so I compared them. If I was more advanced, that’s the kind of thing I’d probably just know immediately. I think I was playing around with blending at some stages too - an unnecessary thing that was just for my own experimentation. I wasn’t treating it like a race. Placing too much emphasis on the history stack can be misleading, as it doesn’t tell you which parts were for my own fun, and which parts were to achieve a result.

[Soupy (Tim)]

@Underexposed

channel mixer rgb offers the ability to normalize the channels. I have tried that and struggled just as much as without it to get the desired result. If I understand right, using it maintains the gray level. Is it worth it?

From Aurelien’s introducing color calibration,
“This also introduces much requested normalization options, that will keep the sum of parameters to 1”

I haven’t used the new module yet, but my understanding is when normalization is ticked R+G+B = 1 for that channel. This ensures greys stay grey, which is desirable when you have neutral grey to start with (and you want to keep them that way). But in the cat image we don’t have neutral grey to start, we have strong orange cast, so you should leave normalize unchecked.

[Underexposed (Bill Martz)]

@Soupy I’m not criticizing, just emphasizing your persistence. Remarkable. You found a really good combination of settings.

@Soupy

This ensures greys stay grey, which is desirable when you have neutral grey to start with (and you want to keep them that way). But in the cat image we don’t have neutral grey to start, we have strong orange cast, so you should leave normalize unchecked.

That’s a good point.

@gaaned92

I don’t understand why you make things complicated. It is just to to add the complementary color

I used neutralize colors in color balance, once, then, twice, then a third time, but it didn’t get rid of the yellow entirely. Plus, I tried to do it manually, using dt, for quite some time, but couldn’t get rid of the blue belly. You’re using ART, and it seems to be easier with ART. I tried the 1800 degrees in white balance, but that was way off in dt. Channel mixer was the way to go, and I made several attempts at it to try to develop some feel for what would happen when I moved a slider. I have made some progress learning how to get two spots equalized. Then I made life difficult by trying to do that with three spots. Not able to equalize all three, but came close enough, and I got better at it.

[Soupy (Tim)]

@Underexposed

I’m not criticizing, just emphasizing your persistence. Remarkable. You found a really good combination of settings.

Thanks Bill. I didn’t read it as criticism, but even if it was I wouldn’t have a problem with it - I’m more of a ‘critique’ guy than a ‘showcase’ guy - more opportunity to learn.

[gaaned92]

@Underexposed

You’re using ART, and it seems to be easier with ART.

I quickly made a haldclut to get rid of the cast and played with it (neutral profile)

[Underexposed (Bill Martz)]

@gaaned92

I quickly made a haldclut to get rid of the cast and played with it (neutral profile)

I read about haldcluts on RawPedia. I would have to do a lot more studying to understand what you did. What puzzles me at the moment is how the yellow is taken away while at the same time the blue belly is corrected. Seems like opposing processes, but it does it all at once.

dt’s color balance tries to take away the yellow, but only partially does so, and affects a slight amount of the blue belly. Of course, I have been trying to do correction without masking.

[gaaned92]

To generate the Haldclut:

• neutral profile with photo
• I used the ART/ local editing/color/tone correction/color wheel to add the orange complementary color and going a little to far to get a light blue cast. This is like subtracting the orange cast. No mask
• generate an ARP file
• load the haldclut identity tiff photo, apply above ARP, generate a PNG 8 bits, rename, put in my haldclut custom files. done.

Using the ARP and the haldclut 100% give the same output.

The interest of the Haldclut is that you can modulate the correction. That can surely be done with layers in DT.

@Underexposed

What puzzles me at the moment is how the yellow is taken away while at the same time the blue belly is corrected

Playing other ways with WB, color mixer and so on, did not permit me to get the same result with so little effort. And as you I am surprised.

[Underexposed (Bill Martz)]

@gaaned92 Thanks, I appreciate your responses.

[Underexposed (Bill Martz)]

After much trial and error, I came up with this.

DSC_2981_art_1_09.jpg.xmp (16.4 KB) dt3.3

The cat’s belly now has gray with a touch of red. I used color balance with masking to get the neutralizing color, which is a shade of green. I turned that off to have a result with just channel mixer. The upper right corner is too red, but getting rid of that threw everything else off.

I followed @Soupy’s lead in using linear prophoto RGB as the input profile, but I have no idea what lead him to choose that.

[Soupy (Tim)]

@Underexposed

I followed @Soupy’s lead in using linear prophoto RGB as the input profile, but I have no idea what lead him to choose that.

That is my habit now for all pictures, as pro photo rgb is bigger than linear rec 2020. I do flower photography and the benefits are particularly noticeable on flowers with highly saturated red or magenta.

[Underexposed (Bill Martz)]

@Soupy

pro photo rgb is bigger than linear rec 2020.

Does the difference show up when you convert to sRGB when you export it as a jpeg?

[Soupy (Tim)]

They do.

Linear rec 2020:

Linear pro photo rgb:

Linear rec 2020:

Linear pro photo rgb:

Of course more saturated isn’t always desirable, but I use it as default.

[Underexposed (Bill Martz)]

@Soupy

They do.

It is noticeable. Do you ever have anything printed? If so, does the difference still show up? Why isn’t pro photo rgb the default?

[Soupy (Tim)]

@Underexposed

It is noticeable. Do you ever have anything printed? If so, does the difference still show up?

Sadly not yet. Hoping to cross that bridge next year - just been focusing on digital development this year. But if colour management to the printer was handled correctly I don’t see any reason why the difference wouldn’t show up.

@Underexposed

Why isn’t pro photo rgb the default?

Not sure, it is in Rawtherapee. I was even playing with ACES ap0 for a while, which has all visible colours, but it sometimes produced weird results. I have seen pro photo give a slight blue cast, which could be a deterrent for using it on black and white images, but its very minimal and wouldn’t be noticeable in vast majority of colour images. (This comes back to Elle Stone’s “well behaved” colour spaces , where well behaved basically means ability to visibly produce grey when r=g=b, Are your working space profiles well behaved?) Rec 2020 is better behaved than Pro Photo rgb. That’s about the only advantage I can see that it has for working space. But I’ve no idea if that’s the dev’s reasoning for selecting it as default.

[pitbuster (Felipe)]

@Soupy

But I’ve no idea if that’s the dev’s reasoning for selecting it as default.

I do not know their reasoning, but ProPhoto RGB going outside of visible spectrum may be one.

Anyways, changing input profile to Rec2020 or ProPhoto are hacks, as we don’t know how the camera RGB space compares. Hopefully, Filmic and the new CAT in Color Calibration should help manage out of gamut colors gracefully.

[afre (Alan)]

Another simple attempt at the feline.