Magic Lantern team has done it again: Raw histograms, raw zebras, ETTR
hint and even Auto-ETTR are of the spin-offs of their discovery how to
access the raw buffers.
What's it all about? We know that a single raw image contains a
relatively large dynamic range (11 to 14 EV). In order to make use of
this dynamic range it is necessary to expose such, that only specular
reflections and actual lights are clipped in raw. This is a matter of
trial and error on most cameras, since the histogram is calculated from
the jpeg data, which clips about 1 or 2 EV levels below the raw data.
Recent Magic Lantern nightly builds feature raw zebras (colored areas
where overexposure is to be expected, similar to clip warning in a raw
converter). The histogram shows how much EV values are still available
until highlights are clipped. This makes it easy to "expose-to-the-right".
or (the inventor):
A loadable module even allows for auto-ETTR, which sets exposure values
on a button press.
All this is still experimental and works on some EOS cameras only. To
try you need to install stable Magic Lantern v2.3 first, then get the
most recent nightly:
(simply unzip and replace the files on your CF or SD card).