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Subject: Re: raw 3.1 professional custom profiles for highend digital cameras



Lawrence, I think you are correct that we lack the tools to place that improtant high value where it belongs, but neither did we with transparency. You can either leave a little headroom for error (which I prefer) or use ACR highlight recovery like Bruce recommends in case you slightly blow the highlights. It would help if the camera makers gave us a histogram which displayed the raw data rather than that of the JPEG 8 bit gamma corrected data. Of course, we also want all three channels displayed!

The 16/15+1 issue derives from Photoshop's use of signed 16 bit integers for its 16 bit calculations. Since the sign takes 1 bit, that leaves 15 bits for the data. According to Bruce Fraser in his excellent ACR with Adobe Photoshop with CS2, this was done so that there would be an unambiguous midpoint for certain calculations. If you want a midpoint, an even number won't do, but I find it odd (pun intended) that both of these numbers are odd.

16-bit signed integer: -32768 to +32767
16-bit unsigned integer: 0 to 65535

For an interesting discussion of dynamic range of digital as compared to film see Roger Clark's essay on the subject. Roger (MIT PhD in astrophysics) approaches the matter with true scientific rigor, as does Norman Koren to whom I alluded earlier. Most of us photographers are in the peculiar position of being neither scientist nor artist, but Roger and Normal are both.

Astronomers (who often have to deal with very wide dynamic ranges) use a program called ImagesPlus which can handle 16 bit unsigned integers.



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