Michel Joly de Lotbinière wrote:
But the remaining problem is this: shadow detail was removed from images when viewed in a color managed application with the video LUT loaded, while it was present when viewed in a non-managed viewer with the video LUT loaded.
So, was the dispcal ambient light -a option the right correction to use to solve the problem of disappearing color-managed shadow detail?
Probably not. The problem described in what you quoted is because the source profile and destination profiles don't have matching black points, and the process being used doesn't map one to the other. [Another trap is to use the V2 sRGB profiles from the ICC website - they are broken, don't use them. Use the sRGB profile supplied with Argyll V1.1.0 RC1 instead.] To fix this you either need to use BPC (Black Point Compensation) if it is available in your CMM and will work with the gamut mapping mode you are using, or if you are using Argyll to create your CLUT destination profile, make sure you give it the source profile as its source gamut, and when using the profile use an intent that does gamut mapping (such as perceptual or saturation).
How is it possible to get those other intents into the generated profile so I can try out the gamut mapping method? At the moment, the LUT profile just has the "relative colorimetric" tables in it.
Supply the source profile as the argument to the -s or -S flags.
What options do I give colprof to generate the other tables? I'm uncertain: what to specify as a reasonable "source color space" -S option that would enclose most of the usual colors in digital photography images? I.e. something a little larger than sRGB, but not too large? Or use the LCD manufacturer's supplied icc profile (without calibration curve) for the LCD panel, that the iccview.de comparision measures as 80% of the sRGB volume--should I use that? Or should I use some reasonable profile for reflective media (e.g. a typical inkjet printer)--but as I'm not looking at reflective media while editing pictures, how can that be a correct choice?
You can try various things, but ideally you want to use a profile for the space your image files are in. Note that if your image files are in a very large gamut colorspace (such as Lab or ProPhoto etc.), you will probably have to supply a supplementary gamut too (-g), if you don't want the output to be over compressed and dull. Graeme Gill.