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: WAYNE BRETL via colorsync-users <email@hidden>
- Date: Wed, 8 Jan 2020 09:44:47 -0700 (MST)
- Importance: Medium
Jack Holm published a paper exploring the reported chromaticities of the
spectral locus based on measured sensor responses and several choices of
matrixing to produce colorimetric values. He noted that all the reportable
colors for a given sensor would lie within this locus, and that the locus might
cover a gamut smaller or larger than that of the eye.
http://www.color.org/documents/CaptureColorAnalysisGamuts.pdf
I expanded on this to study the result of spectra of various widths, thus
representing colors within the spectral locus, in a paper published by SMPTE:
Theoretical and Practical Limits to Wide Color Gamut Imaging in Objects,
Reproducers, and Cameras
https://ieeexplore.ieee.org/document/7269291
In this paper I confirmed Holm's statement that some sensors (those with narrow
spectal responses) would produce a colorimetric gamut limitation when used in a
practical sytem with reasonable raw-to-color conversion parameters, and also
showed how the difference from accurate reproduction would get worse and worse
the closer the color approached the limiting reported spectral locus. In other
words, although the conversion parameters hypothetically are unrestrained ("I
can make any color I want"), practically, they must be designed to give
reasonable reproduction of spectra from objects having common
not-so-highly-saturated colors, such as skin tones and the colors on a MacBeth
test chart. If the sensor has a gamut limitation, it is not practical to
increase the size of the converted color gamut to approach the visual spectral
locus, because the common colors will then become obviously over-saturated. I
believe Sony has realized this in the design of their digital cinema cameras,
because some of their publicity mentions wide spectral response to support wide
color gamut.
Summary: while I agree that sensors do not have a color gamut, they do have a
signal gamut, which inevitably gets translated into a color gamut in any useful
system.
> On January 8, 2020 at 5:08 AM Roger Breton via colorsync-users
> <email@hidden> wrote:
>
>
> I agree, Edmund, this type of discussion is good. The List is awfully quiet
> these days...
>
> / Roger
>
> -----Original Message-----
> From: colorsync-users
> <colorsync-users-bounces+graxx=email@hidden> On Behalf Of
> edmund ronald via colorsync-users
> Sent: Wednesday, January 8, 2020 2:13 AM
> To: Iliah Borg <email@hidden>
> Cc: 'colorsync-users?lists. apple. com' List <email@hidden>
> Subject: Re: Humans (and cameras and scanners) do not have a color gamut (?)
>
> BTW I think this type of discussion is quite helpful because it exposes all
> sorts of computer geeks and photographers who lurk here to the idea that what
> they are doing is twiddling the buttons on some very cumbersome tech that is
> quite distant from what humans perceive. This can be demoed easily when one
> takes a multispectral capture, and suddenly realises that although a lot of
> information has been stored it is hard to transform this back into valid
> dense-impressions.
>
> Edmund
>
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