Re: Humans (and cameras and scanners) do not have a color gamut (?)
Re: Humans (and cameras and scanners) do not have a color gamut (?)
- Subject: Re: Humans (and cameras and scanners) do not have a color gamut (?)
- From: Andrew Rodney via colorsync-users <email@hidden>
- Date: Wed, 8 Jan 2020 14:28:31 -0700
Wayne, let me add this exact copy and paste from Jack when we discussed this
topic many years ago:
--------
A raw image does have a color space if we allow non-colorimetric values to be
called color space values. If we don’t allow this then only colorimetric
cameras (of which there are very few) have color spaces.
I think it is easer to allow non-colorimetric color spaces and use
“colorimetric color spaces” than to invent a new term for non-colorimetric
color spaces. (Actually, about ten years ago I proposed the term “spectral
space” in ISO but no one liked it.)
What I think is misleading is to give the impression that non-colorimetric
cameras have a well-defined relation to colorimetry. Yes, we can estimate
colorimetry well enough for practical purposes but different estimates can
produce different results and be equally valid.
It is important that critical photographers understand this otherwise they
might wonder why they get different results photographing the same scene with
different cameras, even when they use the same raw converter. Or, why different
conversions to scene-referred produce different results for the same scene and
camera. You need to know there is judgment involved in designing the conversion
otherwise you won’t know to perform evaluations to see what conversion you like
best.
Jack
-----
The bit about what's important to critical photographers will likely be lost on
someone who just posted a few minutes about photographers and unlike some here,
are isn't an actual (trained or professional) photographers.... <g>. As one, I
think I can speak for and as a critical photographer.
Andrew Rodney
http://www.digitaldog.net/ <http://www.digitaldog.net/>
> On Jan 8, 2020, at 2:21 PM, Wayne Bretl via colorsync-users
> <email@hidden> wrote:
>
> Arrgh - addressing problems - went only to iliah and not the whole list as
> intended
>
> -----Original Message-----
> From: Wayne Bretl <email@hidden>
> Sent: Wednesday, January 08, 2020 2:13 PM
> To: 'Iliah Borg' <email@hidden>
> Subject: RE: Humans (and cameras and scanners) do not have a color gamut (?)
>
> See Jack Holm's paper, which I posted above, where he derives the spectral
> locus of a combination of a sensor's outputs and a subsequent matrix:
> http://www.color.org/documents/CaptureColorAnalysisGamuts.pdf
>
> Although he does not show the sensor outputs themselves, they have reached
> their extreme possible ratios when the stimulus is a single wavelength, and
> therefore a pseudo chromaticity chart could be plotted using the ratios of
> one channel to the sum of the three on one axis and a ratio of a second
> channel to the sum on the orthogonal axis. This chart would have a defined
> gamut of sensor values (inside the spectrum locus) but would not represent
> colors per se until processed through a matrix.
>
> Holm shows the resulting chromaticities for multiple sensors and several
> reasonable matrices. He includes cases for motion picture negative film that
> clearly show a triangular gamut limit (spectral locus).
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