Opening Comment: In talking with a friend, I realize I should mention how narrowly defined this color management problem and solution are. I've limited myself to trying to get the colors to match between cameras with different sensors at the initial stage of image processing. I have done _nothing_ to address the issues of display to display, nor display to print color variations. Those two topics are equally thorny and well beyond the scope of this series of blog entries.
After uncovering a hole in the color management camera list, I worked on generating the needed .dsp color "offset" files. Now I need to take a look at the results to see it's been worth the effort.
As an overview, I took DPReview RAW files for cameras I was interested in creating .dsp files for, ran the RAW files through a two application process, then transferred the results into a Linux system where the RawTherapee image processing application lives. Have a read through the two blog entries linked in the prior paragraph for a more complete description.
In this blog entry I compare images of the XRite Color Checker Chart with different Color Management selections. Without further ado, here are the results.
[As always, click on the following image and have a look at the image at 100 percent resolution to see whatever there is to see.]
Comments -
Starting with the "No Color Management" option we can see that the Sony A6300, A7, NEX-5T, and A7S images of the XRite ColorChecker Chart are a little "dull" looking and the colors don't look like what we'd expect them to. They are "off" and not correct.
The RawTherapee "Camera Standard" selection helps the image colors appear brighter and clearer. I know, these are non-technical terms, but I think they get the point across. There are slight camera to camera color variations even though I did the very best I could to get the white and darkest gray patches to match between the images. This is what I observed to begin with. This is the arrow to the rabbit hole I fell down for these three blog entries. It was this subtle camera to camera color rendition variation that made me wonder what was wrong.
Coming to the Custom DSP Color Management solution I see that the images align very closely. These images use the files I generated based on DPReviews XRite ColorChecker RAW files. The A6300 yellow patch looks just ever so slightly "dull" compared with the other Custom DSP images. The difference is very very subtle.
The A6300 has a dual luminant .dsp file built into RawTherapee. It includes Look Table and Curves options. The base image with Look Table enabled yellow patch appears "duller" than in the Custom DSP Color Management A6300 image.
Enabling Curves brightened the yellow patch to a more vibrant state. It's still very very slightly different than the Custom DSP Color Management images from the other cameras.
Yes, color management is a rather tricky business. Just the slightest differences in setting image Curves outside the Color Management system changes colors surprisingly quickly. Further, using the Curves function inside the Color Management system changes things yet again.
All this taken into consideration, I feel the Custom DSP Color Management "offset" files give a pleasingly consistent, common color rendition between various sensor outputs. The Adobe and XRite software appear to work. Further, I feel it's more consistent between different sensor outputs than, say, "Camera Standard", so, therefore, worth the effort.
For the cameras that are supported with dual luminant .dsp files, I think I can accept the slight color differences between them and the Custom DSP images on my unsupported by this higher color management specification cameras.
Truth be told, my color management requirements aren't that stringent. However, if they were, and if it were for some reason critical that I get absolute color accuracy, I could do a couple things. The first would be to buy an XRite ColorChecker chart and create my own dual luminant daylight/tungsten temperature files. The second would be to include an XRight ColorChecker chart in my photographs.
As I'm happy with the current updated solution, I think I'm presently "good to go."
Resources -
RawTherapee Color Management System
How to get LCP and DCP files into RawTherapee
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