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: Rich Wagner via colorsync-users <email@hidden>
- Date: Mon, 13 Jan 2020 15:02:00 -0700
This gets a bit off-topic, but it is relevant to the prior discussion and may
be of interest to some on this list.
> On Mon, 13 Jan 2020 12:52:18 -0500, Henry Davis <email@hidden
> <mailto:email@hidden>>wrote:
>
> One can find all sorts of expert ?scholarly? work about how animals percieve
> color. You bring up tetrachromatic, and there are other theories out there
> about animal perception. They are thrown around as ?facts? when a few
> decades ago they would have only been counted as speculations.
At this point, Henry, you are simply displaying a broad ignorance of science,
and in particular, biophysics, which makes further discussion difficult. Yes,
there was a lot that was not known about the physiology of “animal vision,”
including color perception (and a lot of other science!) decades ago, and much
has been learned since then. When I was in grad school working on my PhD in
biophysics (electrophysiology), much of the science involving the
electrophysiology of photoreception was in its infancy. Neher and Sakmann
received the Nobel Prize in 1991 for their development of the “patch clamp”
technique that allowed the measurement of femtoamp currents passing through
single ion channel molecules in cell walls. I spent more time writing software
for data acquisition and analysis and Markov modeling than I did doing
experiments. It was a very exciting time during which many of the fundamental
mechanisms of cell physiology, photoreception, phototransduction and vision
were unraveled.
A lot has been learned since then, as the result of a lot of hard, meticulous
work by dedicated scientists. Vision is a phenomenally complex process, and
although much of it is now fairly well understood and is not controversial,
color perception is still an active area of research. Regarding what’s known:
there is an excellent online summary of the science behind the organization of
the retina here:
https://webvision.med.utah.edu/book/part-ii-anatomy-and-physiology-of-the-retina/photoreceptors/
and color vision here:
https://webvision.med.utah.edu/book/part-vii-color-vision/color-vision/ and
color perception here:
https://webvision.med.utah.edu/book/part-viii-psychophysics-of-vision/color-perception/
This is not a collection of "a lot of theories being waved around.” This is
now scientific consensus. Regarding what’s not known and is currently under
investigation, look here: Visual perception -
https://www.sciencedirect.com/journal/current-opinion-in-behavioral-sciences/vol/30/suppl/C
There are some fascinating articles in this special issue volume, including a
review of cone fundamentals and CIE standards. Other articles are mentioned
below. The 36 or so articles can be downloaded free.
It is accepted fact that color vision processing in the primate visual system
is initiated by absorption of light by three different spectral classes of
cones. Therefore, color vision is described as being trivariant or
trichromatic. You can find graphs of the spectral sensitivities of the S-cone,
M-cone, and L-cones online (above). These spectral sensitivities have been
measured, they are not hypothetical. If you are colorblind, you do not perceive
color as most people do. This is also not controversial. Most colorblindness is
due to missing or defective cones. The molecular genetics behind most
colorblindness is now also fairly well understood.
Tetrameric color vision is not “hypothetical” or “theoretical." There are
humans (women) with tetrachromacy, who have a fourth type of cone. To match the
sensory effect of arbitrarily chosen spectra of light within their visual
spectrum requires mixtures of at least four primary colors. It was once thought
that this was exceptionally rare in humans, but that remains an open question.
It is certainly not common. (http://www.digitaljournal.com/article/326976,
https://www.bbc.com/future/article/20140905-the-women-with-super-human-vision).
There is a great article on tetrachromacy in humans in the volume mentioned
above (Tetrachromacy: the mysterious case of extra-ordinary color vision.
https://www.sciencedirect.com/journal/current-opinion-in-behavioral-sciences/vol/30/suppl/C)
Most birds are known to have retinas with four spectral cone types that mediate
tetrachromatic color vision. The fourth cone is variable across avian species,
but it primarily detects ultraviolet light. There are also pigmented oil
droplets in the photoreceptor cells of birds that filter light before it gets
to the outer edge of the cells, that give birds a larger color spectrum than
that of humans. To study how birds might use this tetrameric system, the
scientists in the article I sent previously created a tetrameric,
spectral-based camera that mimicked real animal spectral sensitivities that
allowed them to visualize the raw data that would be collected by
photoreceptors. This cutting edge research was published in one of the most
respected scientific journals in the world.
(https://www.nature.com/articles/s41467-018-08142-5)
In this era where there has been a great loss of respect for science, and tons
of misinformation and false information spread across the internet, I think it
is important to remain grounded on the scientific basis of our understanding of
the world. Engineers certainly will, as even the avian research described
above could be useful in designing sensors with better detection abilities for
collision avoidance systems on vehicles, and so on. Understanding and modeling
the world around us has been, and will continue to be, the basis for a lot of
innovation.
—Rich
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