Did a little more analysis of UCSB\'s colorchecker RAW file. Here is the fractional difference (G2-G1)/(G2+G1), after median filtering both channels to reduce the column gain fluctuations:
The deviation from pure gray is an indication of channel imbalance. The patches that seem to be different are the black patches, where we are dividing by a small number which amplifies fluctuations; but the rest is remarkably uniform, spot checking indicates the fractional difference of the two greens is a few tenths of a percent, which would not be enough to cause serious nastiness.
This is quite different from skibum\'s first copy, which showed a substantial difference in yellow in one direction, and a difference in cyan in the opposite direction. I\'ll have to go back and dig up my data on that one, but I seem to recollect the difference was several percent. Here, UCSB\'s copy doesn\'t show any dramatic difference between yellow and cyan patches.
Tentative conclusion would be a bad batch among the first run of cameras.
Nov 12, 2009 at 04:58 PM
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