A link within the 2003 article cited by Chuck was interesting--it
updated it for 8/2011.
http://www.luminous-landscape.com/tutorials/optimizing_exposure.shtml
It states the red channel is "almost never blown in typical
daylight"--the LCD histo may be deceiving. I am not so sure 'bout the
red channel bit. Seems easy enough to blow the red channel sometimes.
I don't even think the RBG zebra or live view RGB
histo with CHDK is from RAW data though it was discussed in the
developers forum on a few occasions.---see below
"It would be possible to generate a true raw histogram from raws that
had already been shot. This would be quite slow (probably a couple
seconds if you sampled every pixel from disk, and a bit less if you
took it from the raw buffer right after the shot.) A variant of this is
already available in script with shot_histogram. Similar data is not
available from the preview, and this is probably a hardware limitation.
It might be possible to come up with some experimentally derived
modification to the live histogram to give you better feedback about
the raw."
So perhaps it wouldn't be that hard to have a one button ETTR exposure
for an image with a bit of updated firmware. The best S/N shot to
start with for a black cat sitting on a coal pile is a grey cat at
least for a DSLR but not my OM.
Why not a Raw histo or Zebra on half press, Mike
--
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