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: Fri, 10 Jan 2020 22:09:04 -0700
There is a problem. "There is no *color* a camera [I would say sensor] can't
see" implies that cameras see colors. This would imply they see colors, but
still (as we have said) put out signals that aren't colors. (Why not?)
Cameras sense spectra.
To me, to be consistent, you must say that sensors sense ("see") spectra, and
when their signals are converted to a numerical color specification, may have
certain ranges of color they cannot represent, and/or produce certain numerical
values that are not colors (outside the human spectral locus), and/or represent
colors that are outside a specific color space.
-----Original Message-----
From: colorsync-users
<colorsync-users-bounces+waynebretl=email@hidden> On Behalf Of
Andrew Rodney via colorsync-users
Sent: Friday, January 10, 2020 9:25 PM
To: 'colorsync-users?lists.apple.com' List <email@hidden>
Subject: Re: Humans (and cameras and scanners) do not have a color gamut (?)
And the hits keep on coming:
1. Dr. Roy S. Berns from RIT stated, in Billmeyer and Saltzman’s Principles of
Color Technology: "Color gamut: Range of colors produced by a coloration
system." Color gamut applies to systems that produce color (Printers, TVs
Displays, projector) and color spaces as well. Only devices, or systems, that
render color have a color gamut. Digital cameras do not have a color gamut
(they have a color mixing function). Same with scanners.
2. Program of Color Science / Munsell Color Science Laboratory
https://www.rit.edu/cos/colorscience/rc_faq_faq3.php#255
Q. Digital image sensors (such as those used in digital cameras)use red, green,
blue ink-based color filters to generate color. Do they therefore have a color
gamut that limits the range of colors that they can detect?
A. Let's start with the short answer to your question; there is no such thing
as a camera, or scanner, gamut. A gamut is defined as the range of colors that
a given imaging device can display. To say that a camera had a gamut would be
to imply that you could put a color in front of it that it could not possibly
respond to. While it is certainly possible that two colors that are visually
distinct might be mapped into the same color signals by a camera, that does not
mean that the camera could not detect those colors. It just couldn't
discriminate them. For example, a monochrome sensor will map all colors into a
grayscale image and encode it as such. Certainly the encoding has a gamut (in
this case a lightness range with no chroma information), but did the camera
responded to all the colors put before it. It is the encoding that imposed the
gamut. In the color world, encoding is based on some explicit or implied
display. For example, sRGB is a description of a display and therefore defines
a gamut (but only if the sRGB values are limited in range). If a camera encodes
an image in sRGB, that doesn't mean that the range of colors the camera
detected are only from within the sRGB display gamut, but it means the camera
data have been transformed to best use that sRGB encoding. As long as a camera
has three or more sensors that span the visual spectrum, then it will respond
all the same stimuli as our visual system. Whether the camera can discriminate
colors as well as the human visual system will depend on the encoding of the
camera signals, quantitization, and the details of the camera responsivities.
(To return to the black and white system, that camera encodes all the colors
into a gray scale. They could then be displayed as any color within a given
display, but many colors from the original scene would be mapped to the same
values.)
Since there is no such thing as a gamut for an input device, then there is no
way to compute it or calculate a figure of merit. Generally, the accuracy of
color capture devices is assessed through the accuracy of the output values for
known inputs in terms of color differences. Also, sensors are sometimes
evaluate in terms of their ability to mimic human visual responses (and
therefore be accurate) using quantities with names like colorimetric quality
factor, that measure how close the camera responsivities are to linear
transformations of the human color matching functions. Doing an internet search
on "colorimetric quality factor" will lead you in the right direction.
3. https://www.provideocoalition.com/camera-not-color-gamut/
Your camera does not have a color gamut
4.
https://www.arri.com/en/learn-help/learn-help-camera-system/frequently-asked-questions/frequently-asked-questions-on-color#accordion-44070
<https://www.arri.com/en/learn-help/learn-help-camera-system/frequently-asked-questions/frequently-asked-questions-on-color#accordion-44070>
In an image that is delivered from the sensor of a digital camera, the values
of the primaries relate to the amount of light seen through red, green and blue
color filters. There are no colors a camera can’t see, so it does not really
make sense to talk about the gamut of a camera. It is, however, necessary to
describe the color space used to encode the colors, which in case of the ALEXA
camera is called the ALEXA wide gamut color space.
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