Kai-Uwe Behrmann schrieb:
Gerhard,
I forgot to mention value 255 is defined as white in cineon and value 95
as black.
Kai-Uwe,
OK, then I understand what you mean.
Not knowing about Cineon format before, I took a brief look at the
Cienon web site, and IMO http://www.cineon.com/conv_10to8bit.php sais,
that reference white is encoded as 685 (not 255), and black as 95 (as
you say). However, these values seem to be only the default values, and
my interpretation is, that the defaults may be replaced by individual
values, if a different white or black point is more approrpiate for
rendering a particular Cineon image to an output-referred color space.
This web page also specifies, how the 10-bit Cineon encoding should be
converted to 8-bit video RGB encoding, and they specify conversion
variants without and with different amounts of soft clipping. The
described conversion can be IMO easily carried out with TRCs.
But I'm still wondering, which RGB color space they mean with "video
RGB". It looks like they assume an RGB color space with (default) gamma
1.7, but they are not perfectly clear about this issue either, since
they also seem to call this "linear RGB"? And so far, I could not find a
statement, where they would specify any RGB primaries of this video RGB
color space.
Furthermore, the colorimetric properties of the Cineon color space
itself are IMO not specified clearly either. The 10-bit log encoding
seem to be specified in terms of "printing densities", where "Printing
Density = the density above D-min of the negative as seen by the
combination of print film and the illumination of a standard motion
picture printer" (according to
http://www.kodak.com/US/plugins/acrobat/en/motion/support/dlad/kodak_digital_lad_users_guide.pdf).
But which spectral properties do the assumed film and the "illumination
of a standard motion picture printer" have? A densitometric match does
not necessarily imply a colorimetric match, the same densities may
result in different observed XYZ colors for different films.
Regards,
Gerhard
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