A friend of mine forwarded me this link to an interesting article about Digital ISO (you'll just have to plow through the excessive real estate populated by ads...) --> the article references a noise test video where testing was performed on a Canon 7D that showed that ISO 160 was cleaner than ISO 100 and that ISO 640 was on par with ISO 100! The tests appeared to have been done with video (rather than still images), but it definitely raises some questions. The article goes on to discuss / theorize about why some digital cameras will produce higher quality / less noisy images at certain higher ISOs. Has anyone here this type of analysis? The last page of the article suggests some test methods, but I am very curious as to what the best method to quantitatively test my own equipment and compare it to other camera models.
Perhaps what they are seeing is due noise being introduced by after the fact multiplying light values, b/c ISO640 is not a real gain setting on the non pro canon bodies. Check around BPN for the reference, I think Arash brought this up