Thanks Gabor. I'll recheck, but when I did the measurements initially (at least with firmware 1.0.9) I found that appropriate delta was approx. -0.41.
instead of measuring it, it can be calculated easily. For example ISO 320 is from ISO 400. The clipping levels with ISO 400 are around 15300, and with ISO 320 this is around 12645 (these are the same for the other combinations, like 160/200, 640/800). The black level is always close to 2048.
(15300 - 2048) / (12645 - 2048) = 1.2505...
This is the proportion of the "shrinking" the camera performs on the raw data. 1/1.25 = 0.8, and in fact, the ISO 400 pixel values are multiplied by 0.8. 1.25 is a bit less than the cuberoot of 2. 1.25^3.1 is ~ 2 and 1/3.1 = 0.3225.
See the "combing histogram" in http://www.cryptobola.com/PhotoBola/Canon7D_ISO.htm
Added: the clipping levels may differ from copy to copy, but not relevantly. I found these values in shots of about five copies, among others with firmware 1.0.9.
Thanks Gabor, that is indeed the same as the math we're using. Once I get back to the office I'll check to see what the source of the discrepancy is.
Thank you Gabor for the interesting and informative"ISO settings with the Canon 7D" article. Opened my eyes.
This will be fixed in the final release. Thanks for pointing it out, Gabor.