Now how to do that in scene-referred without changing color too much if at all.
You shot that pretty dark for an indoor shotā¦ I wonder if you could just start with a brighter image and then less correction is neededā¦ also if you use a color checker and use that for wb and color you might not have to worry so much about how your exposure and tone are changing colorā¦ I guess its comes down to what your perception of what the shot should look like and how to best represent that ???
I used the Sekonic chart middle gray to create an accurate reference under my 5000K lighting. L*=49.7 a=0.03 b=-2.2 So, the color is correct. I could definitely start with a brighter image by increasing exposure +1ev. Iām not so sure that it would make any difference though after calibrating the chart.
I had to increase the exposure 1.418 ev to calibrate the chart. If I ettr the shot 1.33 ev and re-calibrate, would that help to hold color when doing scene referred adjustments?
Me neither. One of my Gurus, Elle Stone, said:
āScene-referred RGB data is bounded only by Chromaticity.ā ā¦ in other words, Lightness is not.
Way to technical for me. Anyway thanks for sharing.
The operative word in that article is āboundedā, she shows that values of Luminance Y due to editing can not be clipped if someone goes over the top.
Whereas display-referred for 8-bit monitor automatically clips anything over 255.
Maybe L* in CIELAB does not correlate with Y in CIEXYZ.
I have no idea what darktable means by āscene-referredā, so my comment was a general one.
I was using a display-referred module (tone curve) within a scene-referred workflow. Would it be okay continue doing that as long as brightening was kept well under 255 which is always the case for my hobby photography?
Sorry, Mike, I donāt use darktable and have no idea what each āmoduleā does or how it does it. In principle, never exceeding 255 is OK unless there are specular highlights (e.g. sunlit motorbike) that you donāt care about. Iām less sure about ākept well under 255ā, not knowing how much āwell underā is.
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Yes. Its fine. It isnāt 100% optimal, but it works. If you want the best results, make sure Tone Curve comes after Filmic/Sigmoid.
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@paperdigits Advise taken. Iām just surprised that scene-referred doesnāt have a module that preserves color when lightening or darkening. At least thatās my impression.
Its a complicated topics, and Iām no expert, but generally when you change the value (lightness or darkness) you also change the perceived color as well. Iām sure there are plenty of people who can explain it better than I can.
Iām not a technical person so Iām sure that further explanations would most likely be over my head.
This might be a moot point, but having a L*ab adjust module catered to scene-referred might be useful for certain photos where maintaining color accuracy is important.
I donāt think that is possible.
DT uses 32-bit float and tried for the most part to keep operations linear and with a fairly close proportional relationship to the data in the sceneā¦ Then it uses a tone mapper to manage that and bring it to the displayā¦ So you have all that lightā¦you add or subtract exposure to give you middle gray ie put your scene middle grey at that point in the display DNRā¦ Then filmic or sigmoid will map the data on either side of that as you specifyā¦
THere is a dynamic display of this in filmic
A potential filmic-based rendering. Left: your sidecar, with the tone curve turned off (ground truth for colours). Right: filmic with color balance rgb.
But you are correct, the dynamic range of the image is so small that there is no need to compress it with a tone mapper; itās all reflective surfaces. Your tone curve already shows that: the histogram does not come near black and it stays far away from white. In fact, your curve expands the dynamic range (it increases contrast almost everywhere, with the shoulder being above the original input, only a bit of the toe affecting the darker portions in the original.
sRGB histogram without your curve:
With your curve:
Alternatively, your version (with the tone curve) vs sigmoid with the smooth preset:
But again, both with filmic and sigmoid, here we are just making a contrast adjustment.
(Note that the screenshots are not completely what I see on my display, as they are in my monitorās colour space, which does not match sRGB completely, and I did not convert them from that space to sRGB manually. They are not that far off.)
This would be a good place to start:
It also explains the issues with Lab.
The problem is that you have no real control over what happens to values above 1. Anything that changes the shape of the right side of the curve could have unintended consequences. Have you tried Tone EQ with the simple tone curve preset? Itās supposed to work exactly like a tone curve, but of course compatible with unbounded data.
And this part of the manual would probably be useful reading: darktable 4.6 user manual - darktable's color dimensions
Thanks, Todd!
Interesting that it also seems to involve display-referred actions, so not as described by the ICC folks:
The above links to:
I just looked at that. I donāt see any change when I select that preset. Am I missing something?
darktable 4.8
No guided filterā¦ see in masking for preservation of detailsā¦