@nonophuran PM sent.
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D75_5446.NEF (25.9 MB)
D75_5446.NEF.pp3 (13.6 KB)
(no particular licence for this picture, of course)
So, trying it out for myself, with this data
spydercheckr_reference_data.pdf (200.8 KB)
after picking the WB on the grey card exposed to the sun, I adjusted the exposure so the brightest patch would get to L = 97% approximately.
The other grey patches fall pretty well where they’re expected to, in my opinion (not talking about the a and b values, though).
Notes:
- camera is a Nikon D750,
- profile is auto-matched,
- only
base tableis ticked, - the processing profile is derived from neutral.
→ this seems to achieve neutrality in RT.
A few minutes before that, with a different lens and orientation, the sun was behind clouds. With a similar processing approach, I get some compression in the shadows (i.e. they appear lighter than they should, but that could be due to the hand-held and imperfect setup 
)
If I understand my D7200 correctly, when shooting in RAW you don’t need to set up anything in the camera. Everything you can switch on is used only for the in-camera development of the JPEGs. Therefore the input profile of RT is just used to map the values of all four sensor channels to the rgb values of the corresponding pixel.
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Indeed.
Back to the optional Tone Curve and the Look Table: for my D750, I think I found something relative to its origin.
That does not clarify what these two options, in this case, are supposed to do. What “Look” are we talking about? What is that Tone Curve required for? (i.e. when is it applicable?)
Since this git + google groups discussion mentioned in my previous post is almost 10 years old, I doubt I’ll get an answer about the intent of the attached look table (for the D750). But there was some debate pertaining to the quality / usability of the provided color checker shots, back then (perhaps @jdc remembers?). This is getting off topic: should I provide my own shot so it can be turned into an RT-bundled .dcp profile?
@nonophuran
Yes, I remember, or at least approximately…
The problem of the calibration charts is of 2 types (at least)
- these calibration targets are most often close to sRGB or even a little more, especially for greens, this is mainly due to the printing of these targets, which limits the gamut. Isn’t it paradoxical to have a “working profile” in Prophoto (or Rec2020) and use a target in sRGB. We extrapolate a lot and the errors are significant…
- the second point is whatever we say, whatever we do the calibration system is good for an illuminant, the rest comes from empiricism. In this sense, ICC profiles are “finer” than DCPs, but more complex to develop, and even more constrained by the illuminant
Another point to be mentioned is the nature of the grays (for example on the Colorchecker24), putting Pick in the belief that it is a good balance of whites comes up against 2 false inferences.
- the grays are not pure greys…so we do the WB on one color, certainly close to a gray…but
- believing that the variation of the law of white balance is linear is probably wrong
And
- the color matrix is in D65, and probably tainted with error… The illuminant is not pure, Observer it is tainted with doubt.
- I remind you that it is possible to correct the colorimetry with “Abstract profile” (even if this module is controversial… that’s an understatement), by acting at the end of the process (see Rawpedia).
Jacques
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The tone curve has the same roll as any tone curve…to massage the data in to a way the manages contrast more the way we perceive it… the Look table can be applied as noted in the specifications for DCP profiles as noted here
"There is also a LookTable, which is exactly the same as a HueSatDelta Table, but is intended to be applied later in the processing pipe, “after any exposure compensation and/or fill light stages, but before any tone curve stage”
During creation the DCP spec is often used and abused as is evident from all the complaints about various DNG implementations…
There is a lot of good information around DCP files here which may clarify some of your queries including a text file that you can just read through…
Hi Jacques,
I think I understand the problem the way you described it. It’s especially obvious in the realm of colour negative film inversion: one grey spot is never enough, however close to neutral it might be.
In your opinion, with all those limitations in mind, is a new attempt (with a 24 or 48-patch card) for the D750 required, or is the biggest achievable difference too small to even care, because of the nature of the targets and the realistically achievable shooting conditions?
Thanks again!
Hi Todd,
Thanks for responding.
I think I get the Tone Curve concept. Thanks for the link, too.
My main point was, for the specific example of the Nikon D750 DCP currently shipped with RT, to understand from whence this look came, as this was far from obvious in the history of its making, cf. github discussion mentioned supra.
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I can’t recall now without full review but you may have mentioned about starting points and JPG and that’s why you are using DCP as a preferred option?? Or that’s wrong. But I hacked this to work with my Spyder checker and It actually gives a pretty nice result. Maybe not color accurate as some but a pretty nice match to JPG… GitHub - pmjdebruijn/colormatch: ColorMatch
We have to stay very humble… I don’t know. Doing what you suggest is better than nothing, but you have to remain pragmatic by understanding the limitations.
The colorimetric system has more unknowns than equations and all the tools and concepts: ICC profiles, DCP profiles, notions of primaries, illuminants, etc. are approximate models.
For example, the white balance on which I work (temperature correlation) supposes a certain number of sidestepping of reality. To think that it could be otherwise is a utopia.
But there again, it is better that than nothing…provided you know the limits.
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Well one thing you could do is convert one of your files to DNG and then you have a source file for the defacto Adobe DCP file… you could try downloading it as well from adobe and see if they are the same… Picking one of these you could compare it to the one used in RT to see how it might differ…
Then you can also since you have a color checker use the adobe profile editor to tweak that to your hearts desire …
Here Robin tweaks the color using a photo but you could use a colorchecker…there is even a colorchecker tab for xrite cards as well…
But simply tweaking a std daylight shot of your color card might give you a profile that suits you better…
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Hi Todd,
I had seen this repository owner’s contribution to a fork of dcamprof but I was not aware of this other tool.
I’m not sure I understand what you hacked your way into. What’s the input, what’s the output?
The README says:
ColorMatch
==========
ColorMatch allows you to create an ICC standard color profile
based on the color transform your camera firmware uses to
create JPG files. This profile can then be applied to your
RAW files using RAW editing software.
Keep in mind that ColorMatch should be considered as highly
experimental and requires meticulous application of the
procedures below in order to be successful.
WARNING: Keep in mind that ColorMatch comes with no warranty
whatsoever, use at your own peril.
→ is this trying to mimic what we have in RT, in the Exposure module, where we have the ability to auto-match the tone curve to the look of the embedded JPG thumbnail?
Or are you doing something else?
Its taking your jpg and creating an icc to produce or attempt to produce a match.
It obviously works best with a shot from a camera with more patches and it is set up to do so. I have a Spyder checker with only 24 patches but so I had to edit the code to accommodate that. It still does a pretty nice job… what colorchecker do you have again??
same here.
I also have a faulty colorchecker passport that lacks the 24-patch chart, so I only have the greys and the more subtle tones. Wonder how I could franken that into something usable at the same time by dcamprof but that’s a different subject.
if you want to post a raw shot of that I can run it though the colormatch and you can see if the result is of any use… you can tweak the script further… I forget what the default settings that is uses with colprof but you can simply edit those in the script to make a targeted change as well…It the jpg preview in you raw is pretty big I can just extract it but if not the jpg would be needed too…
faulty indeed. I didn’t know they made one like that. If you had a spectrophotometer you could measure each patch and make a reference file, but you’d be missing good red, green, and blue patches to anchor the colorimetric response.
here : Which Input Profile to choose? - #31 by nonophuran
or, in the shade, as mentioned in the screen capture above:
D75_5437.NEF (26.7 MB)
It’s probably imperfectly shot. Limitations I anticipate:
- some glare,
- some cast though I don’t know of what tint (green foliage slightly behind me? honestly, I don’t know, but my balcony is not a perfectly neutral environment, i.e. not contaminated with reflections of sorts)
@ggbutcher, yeah, unlucky me, esp. since I got this passport sealed and second hand (think: old new stock) and the support (at Calibrite’s) has not accepted yet to proceed to anything other than saying “yes, it looks like a manufacturing problem”.
Ya it did come in green…have you been messing with your camera…funny I use legacy WB and your as shot is coming in at 1 for all color channels (UNIWB ???)…just doing an average image spot wb gives what I might expect for the image and of course I could use one of the patches for even better wb…
Usually I do the image pairs using as shot rather than applying a wb… and then just let the blended icc do the match…
I guess I can do a spot wb here on both and then try…
That sucks… “old/new stock” could straddle the X-Rite/Calibrite divide and they’ll end up playing warranty badminton with it…