Hi @jdc , and thank you very much for responding. I had two contexts for asking about the CIECAM02 settings.
The first context is no longer applicable, being some unknown combination of user error and software instability. For some reason the image as shown in the RT UI didn’t look anything like the image as saved to disk and imported into GIMP. The usual “different color management settings” did not apply. I had installed the GTK3 stable version from OpenSUSE Tumbleweed, and it wasn’t very stable:
- The CIECAM02 module kept disappearing, leaving only the little description section visible, with no way to show the actual sliders. The only way to get the CIECAM02 panel back was to exit RT and then delete all the user RT configuration files and start over - this happened so frequently that it was difficult to actually get an image saved to disk.
- Also the left panel wasn’t resizeable, instead would start to resize and then flick back to the default width.
So I uninstalled the GTK3 version and installed the GTK2 version. It took a couple of configuration file deletions and restarts before the CIECAM02 module “stayed put”. But now everything is fine. And it’s entirely possible that the “looks different” problem was partially or entirely stupid user error from comparing actually different images - I have trouble remembering that RT’s default export folder isn’t the same as the folder from which the image was opened for processing.
The second context is that previously I never used the CIECAM02 module, precisely because the CIECAM02 color management options in Preferences ask about the display device and I didn’t know what the right settings should be:
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I think that if the context is using ICC profile color management, and displaying the image on the same monitor that’s used for editing, then the display “white” in Preferences/Color Management should be D50 - is this wrong?
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If the image were to be displayed on a calibrated but non-color-managed monitor (like a TV screen), then likely the actual white point of the device would be the right value, yes?
I decided to try using the RT CIECAM02 module, even not knowing the Color Management settings, because I was using GIMP 2.9’s LCH color tools and blend modes to make a night scene rendition of a photograph taken during daylight. I was having trouble getting the shadow tonality to be sufficiently dark without losing detail completely. It occurred to me that the RT CIECAM02 module might be used to solve the problem, and indeed RT worked very nicely for this purpose. This is why I was asking about “scene luminance” and how it was calculated:
- The image that I exported to disk from GIMP and opened with RT didn’t have any embedded exif information.
- Even if the image had contained all the exif information from the raw file, that information wouldn’t be relevant to the image that was actually exported from GIMP, because the image had already been considerably modified to make a night scene from a day scene.
- Even if the camera raw file from which the image was processed were directly opened in RT, the embedded exif information doesn’t contain the f-number which the RT “on hover tooltip” says is used to make scene luminance calculations, because my manual lenses don’t communicate that information to the camera.
Anyway, I liked the way the RT CIECAM02 module allowed me to modify the GIMP-produced shadow tonality so much that I decided to try using RT to make a night scene from the day scene starting directly from the camera raw file, and that worked out pretty well, too, at least for the tonality. I didn’t really like the color so much, but I’m not all that familiar with using RT. If anyone is curious, the RT-made night scene and some notes on the CIECAM02 settings is on this page under “Processing note”: http://ninedegreesbelow.com/photography/day-into-night.html