Thread: "16-bit" mode.
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  #11  
Old November 17th 04, 12:35 AM
Mitch Alsup
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wrote in message . ..
First I thought it was strange when I found out that Photoshop's 16-bit
mode was actually 15-bit. Then, I though it was stranger still when I
found out there was one additional level (32768; it was explained that
this made certain types of math faster). Now, this evening, I was
writing an applet to extract RAW data from the uncompressed output of
the DNG converter, and decided to create a raw greyscale bitmap 256*256,
containing every possible 16-bit value, to see what PS would do with
them. I assumed that PS would make 0 and 1 0, 2 and 3 1, 4 and 5 2,
etc, but it does not. This is a sample of what it does:

real
16-bit PS values
data

0 0

snip
9 5

2044 19128

snip
2052 19134

4085 32762

snip
4095 32768

Does anyone have any idea why they posterize the data even more than the
15-bit limitation?


This looks like somebody is applying the gamma correction to the RAW data
ouptut = input**2.2 / some-fixed-scaling

Mitch