I am trying to figure out GainMap tags change by ISO in ".dng" file. I came across with this question: https://forums.adobe.com/thread/1410199 and this answer: https://forums.adobe.com/message/6145362#6145362 helped me to understand.
To understand ISO’s effect better, I took 10 pictures and averaged them when ISO was 100. Then I took 10 more of the same scene and averaged them again, but this time ISO was 200. Among the two sets of images, the only change is ISO, i.e. all other parameters are fixed.
Pixel values were doubled in RAW of the average of second set w.r.t the first set, globally, since only the ISO was doubled (as I expected). I also averaged 4 GainMap opcodes separately for the first set of images (ISO100), and for the second set of images (ISO200). Again, when I compared the two sets (ISO100 vs. ISO200), second and third opcodes are exactly the same for the two sets. However, first and fourth GainMap opcodes are different. Can you help me to figure out what is the reason of this difference?
Here I'm sharing the change of GainMap opcodes, which are obtained by point-wise dividing the two matrices which are obtained by the two sets (ISO100 vs. ISO200). Colorbar shows the scale of change. As I mentioned, only first and fourth GainMap opcodes are different, so that I’m putting the two here. The other two are the same with each other.
Thanks in advance for your time.