Re: camera colour spaces
Re: camera colour spaces
- Subject: Re: camera colour spaces
- From: Graeme Gill <email@hidden>
- Date: Wed, 12 Mar 2008 10:54:45 +1100
email@hidden wrote:
The only way my limited understand of colour management is able to
understand this in- camera rendering is to see it as a cryptically
assigned generic input profile followed by an imposed conversion to a
selected colour space. The choice of rendering I can only see as different
input profiles, each one with its own table, or a single input profile
using different custom rendering intents, much as some profile
manufactures use the saturation intent to flavour the colour pallet,
(apparently there aren't any icc standards for this intent.)
It's unlikely there is an ICC style "input profile" within the
camera. In general the sensors are going to be pretty linear,
so if the spectral sensitivities of the sensors are close
to being equivalent to the standard observer, or if an
assumption is made about the statistical frequency and
spectral shapes of typical colors in the real world,
a simple 3x3 matrix is all that is required to transform
the sensor RGB into CIE XYZ values. [There may be
tweaks to this to accommodate any deviation from this
ideal of course.] It's unlikely I think that this matrix
would change with any selection of output file colorspace,
since it is essentially the sensor calibration.
From there it is a matter of rendering the raw XYZ data into
an output referred form, since this is what the expectation
generally is for things like JPG files. Picking a white point,
setting the transfer curve to get the black level and tonal range,
saturation manipulations, out of gamut compression/clipping
and encoding in the output colorspace then follow. It's easy to
see that in this process you can choose from any number of
standard color spaces to encode the final image, as well as
even more variations in the style of rendering.
Graeme Gill.
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