Note: There is a parallel thread on color balance for this camera here: Instead of hijacking that thread, for this thread, I'm looking more at specific tools to do the analysis. Subtle difference, though definitely related.
Given the various (and conflicting) recommendations on what values to use for proper color balance on ASI cameras (ASI2600MC-Pro in particular), I thought I'd try some tests to prove which is "correct". Quick answer: None of them. Which leads me to this post...
What tools can one use to determine the proper color balance settings for the ASI2600MC-Pro camera? I don't want to simply judge what the screen looks like, since my sense of color is not the best, and what is displayed is dependent on a bunch of other system settings that have nothing to do with what is recorded in the FITS file.
Constraint: The camera is hooked to a Raspberry Pi 4B running Astroberry, so I need to use that as the base for any software tools used. I'm not opposed to loading something additional to the distro, but doing the calibration with, say, a Windows laptop with ASCOM and then assuming they apply to Astroberry / INDI is a leap I'd rather not take.
Background: Yes, I "know" that RAW imaging means "direct bits from the sensor", but fact is that there are red and blue white balance settings in INDI, and they do make a difference. From the factory, and according to the thread above, the camera came with WB_R set to 52, and WB_B set to 95. (My recollection is that it was the other way around, but no matter...) Green is apparently assumed as 50. Recommendations just after I got the camera said that the factory settings are odd, and should be overridden to 50/50. I've been imaging with 50/50 since then, and have been happy with the results. Image background has been pretty evenly gray, with no glaring color tint. Stars are relatively assorted in color, etc.
Then the above referenced thread pops up, noting they got an 85/74 setting from ASIStudio. Whoa.
Since I cannot run ASIStudio on the Pi, I thought I'd try playing with INDI and the acquisition app that I do use, which is CCDciel. I put my Flat display on top of the scope, and snapped away. CCDciel displays at the bottom of the window the R/G/B values of the pixel your mouse is over, giving a quick and easy way to display the results of the settings. Trying the current 50/50 setting gives a decidedly unbalanced result. Best seems to be 85/99, which is yet different from all the others.
In tabular form: (1 second exposure)
RB/BB Red Green Blue
----- ----- ----- -----
50/50: 18831 / 25284 / 25284
52/95: 15006 / 25130 / 25130
85/74: 25197 / 25197 / 15425
85/99: 25156 / 25156 / 21388
So, three questions, really:
1. What tool should I use (available for Astroberry) to figure out what setting I should be using?
2. How sensitive is the specific color of "white" from my Flat screen is the result? I.e., could my results be different than the OP in the other thread due only to my choice of what "white" is? Does it even matter?
3. Why am I seeing "stuck" values, such as 25284 in the 1st row, and 25130 in the 2nd? These values are common across a wide area in the image, which is unexpected. At lower exposures, it may be only "stuck" for one color.
Bonus question: In CCDciel I can specify a color balance (R, G, B sliders) for use in Preview. While this doesn't affect the saved image, it very much affects what I see on the screen. I have had to set the Green slider to 50% in order to see a reasonably balanced image from the sky, taken with the 50/50 settings in INDI.
Thanks for the help!