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: Thu, 9 Jan 2020 11:01:13 -0700
Limiting by saturation (overload clipping) of a channel is not the kind of
gamut limit explored by Jack Holm's paper or mine. As you state, it can be
alleviated by reducing exposure. The sensor gamut limitation of interest,
that has no fix, is when one sensor channel (or two, or three) goes to zero
when a particular spectrum is input. If this is a spectrum for which all
three cone responses are not zero, the sensor response, converted to a
color, results in a gamut limit smaller than that of the eye (in practical
cases, where the conversion matrix or LUT has been formulated to provide
close-to-colorimetric results for common broad spectra).
-----Original Message-----
From: colorsync-users
<colorsync-users-bounces+waynebretl=email@hidden> On Behalf Of
Florian Höch via colorsync-users
Sent: Thursday, January 09, 2020 10:49 AM
To: email@hidden
Subject: Re: Humans (and cameras and scanners) do not have a color gamut (?)
Am 09.01.2020 um 18:16 schrieb Henry Davis via colorsync-users:
> Speaking about the color gamut of a sensor may not be a precise use of
> terms but it does seem to relate a conceptual notion about it.
The problem I have with the term "gamut" when applied to sensors is that it
asserts the notion of a limitation that simply does not exist in the same
way like it does for output devices.
E.g. if a sensor gets saturated, there's two ways around that:
1. Reduce the intensity of what is being measured/captured (when possible)
2. Reduce sensor sensitivity (probably the more practical approach when it
comes to cameras)
Which in turn means, when you try to capture something that is "out of
gamut" (only using the term "gamut" here for the sake of the discussion
topic) for a camera sensor (e.g. at least one channel fully saturated), you
reduce exposure time and/or use a neutral density filter and voila, you're
now able to capture whatever signal was previously clipping.
When it comes to output devices that have color gamuts, there simply is no
equivalent mechanism - e.g. on a computer monitor, you can twiddle
backlight, "contrast", "saturation" controls all you want, once you are at
the hard limit imposed by the panel and backlight, there is no way to make
the gamut any bigger. Same for printers.
TL;DR scenes and output devices have color gamuts, hard limits to the range
of colors they contain or can (re-)produce. Input devices
(sensors) do not (notwithstanding later processing indeed usually imposing a
gamut, at least for cameras, and it certainly is arguable that cameras where
you can only get sRGB or AdobeRGB JPEGs but not raw capture have an
effective gamut limitation due to the latter).
Florian.
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