[argyllcms] Re: Quality of camera profile - colour banding
- From: "edmund ronald" <edmundronald@xxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Sun, 27 Jul 2008 13:37:57 +0200
In my experience, which of course is very limited as I don't work for
a camera or sensor company, the simple matrix method is ok if the
matrix is derived from a test image in the lighting which is then used
for the subject matter. I have used commercial software to create
usable general-purpose camera profiles, but in difficult or mixed
light a simple matrix derived from actual measurement of a test image
in that light will always win out. To my eyes anyway.
At the level of the ICC, I have been lobbying for the inclusion of
fields in TIFF/EP for a spectral power measurement of the illuminant
of a scene, and for inclusion of spectral sensitivity curves for the
cells composing the sensor. There are now -medium expensive- solutions
for field measurement of both these curves, and the information
gathered could be processed by any Raw converter to derive decent
color. I have also lobbied to request that all Raw converters be
capable of picking up manufacturer included data including matrices
and rendering profiles when present, but there is industry resistance
as the camera manufacturers don't want to publicize either sensor data
or matrices and renderings, and Adobe likes to use only their own
data.
Edmund
On Sun, Jul 27, 2008 at 1:23 PM, Gerhard Fuernkranz <nospam456@xxxxxx> wrote:
> Klaus Karcher wrote:
>> edmund ronald wrote:
>>> In my experience, current dSLRs are pretty well linearized in Raw mode.
>>> Obtaining decent color from them is a matter of locating the primaries.
>>> The raw2xyz transform can be considered to be a matrix.
>>> The problem resolves into a one line Matlab or Ocatve program.
>>> Whether you want to deal with flare, or other secondary phenomena, is
>>> a different issue.
>>
>> Is it usual to get primaries way beyond the spectral locus or even
>> with negative components (e.g. like those in Milan's profiles) with
>> current cameras?
>
> It depends on the method being used. There are several methods proposed
> in the literature for deriving the 3x3 matrix, which claim to work
> better than a simple minimization of an error metric in a least squares
> sense, for a given a calibration target. Some of them seem to make use
> of additional constraints like exact mapping of white, positivity of the
> captured spectra, or particular assumptions about the correlation of the
> captured spectra (e.g. smoothness of the spectra), etc. I haven't yet
> looked into these subjects in detail though.
>
> Regards,
> Gerhard
>
>
>
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