Date: Tuesday, November 01, 2005 9:08 AM

> "Some digital cameras try to record 10-bit (1,024 possible
> values per channel, a billion possible colors). Modern drum
>
> This point is not universally correct. For example, the Canon
> 1Ds and the 1Ds Mark II produce 12 bit files. As for

FWIW, when we have bench tested various current D-SLRs (including the 1D,
D1X and the D2X) the noise (combination of internal & light scatter (aka
lens flare)) is sufficiently large that the last 2-bits of precision are not
typically meaningful.

The 10th bit is more controversial. Nikon reduces Raw files to 9.5 bits
(although they do gamma encoding at the same time) when they do what they
call "visually lossless" compression, but there are many photographers who
rely on detail in the highlights that the Nikon compression flattens out
(because of the gamma encoding) and find that the compression scheme ruins
their images and refuse to use it.

I don't think anyone has tried to see whether a 10-bit linear encoding would
actually be more useful than the 9.5 bit gamma encoded version Nikon uses,
but it'd be a good exercise for a grad student someplace!

Modern zooms that we tested are also limited to about 10-stops (1000:1)
total dynamic range in properly exposed scenes (due to lens flare), which
actually lines up pretty well with the sensors' capabilities.

This is all getting trickier to measure since the very newest cameras are
doing more analog "pre-conditioning" of the data before converting to
digital so at some point the experiments are measuring the circuitry, not
the sensor or lens.--David Cardinal

http://www.cardinalphoto.com
http://www.nikondigital.org

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