Re: Viewer perception of neutral gray
Re: Viewer perception of neutral gray
- Subject: Re: Viewer perception of neutral gray
- From: "Bob Frost" <email@hidden>
- Date: Wed, 5 Sep 2007 10:11:52 +0100
Mark,
1. People have 3 types of color receptors in their eyes,
At the very least, you need to put the word 'most' at the beginning of your
sentence, since it has long been known that some people only have two types
(dichromats), and some only have one type (monochromats) - 8% of men and 1%
of women are partially or completely color blind.
In addition, recent research shows that some women (2-3% ?) have four types
of cone (tetrachromats) like many birds, ampibians, and reptiles. And from
these results, about 99 million women in the world could have this
four-color vision. The extra cone has pigments between the red and green.
Here's a quote from a research paper out of UC, San Diego, by Jameson et al.
in 2001
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11495112&dopt=Abstract
"We use genetic analyses to examine an important position in the gene
sequence, and we empirically assess and compare the color perception of
individuals possessing more than three retinal photopigment genes with those
possessing fewer retinal photopigment genes. Women with four-photopigment
genotypes are found to perceive significantly more chromatic appearances in
comparison with either male or female trichromat controls. We provide a
rationale for this previously undetected finding and discuss implications
for theories of color perception and gender differences in color behavior."
There is also other research suggesting that we all are all tetrachromats -
and that our UV receptors are blocked by the absorbtion of UV in the cornea
and lens - http://www.4colorvision.com/files/tetrachromat.htm.
So the women with the extra receptor may actually be pentachromats, like the
lowly pigeon!
often known as alpha, beta and gamma.
Or more correctly as L, M, and S (long, middle, and short
wavelength-sensitive); Photopsins I, II, and III; Protan, Deutan, and
Tritan; or erythrolabe, chlorolabe, and cyanolabe.
2. Each type of receptor very roughly corresponds to red, green and blue.
There are other reseach papers showing that there is considerable genetic
variation in the pigments in two of our three cones, which cause variation
in our color perception.
<http://www.ncbi.nlm.nih.gov/sites/entrez?Db=PubMed&Cmd=ShowDetailView&TermToSearch=10708034&ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVAbstractPlus>
5. Since we know that "color blind" people exist, it is very unlikely that
most people have equivalent spectral response.
Another variation in color response that is often ignored, is due to the
changes in the color transmission of the lens with age. Here are some
results from a replacement lens manufacturer
showing the difference in color transmission of a 25yr-old human lens and a
54yr-old lens:
wavelength 450 500 550 600 650 700
25yr-old 35% 70% 75% 75% 75% 75%
54yr-old 25% 45% 50% 55% 57.5% 60%
Reduction 29% 36% 33% 26% 23% 20%
As you can clearly see the older lens has 20% reduced red transmission, but
this progressively increases across the spectrum to 36% in the blue. And
this difference is found at a mere 54 yrs of age! It is much greater at 60,
70, and 80.
Last year I had both lenses replaced as they were going cloudy and affecting
my resolution, but with 3 months between the ops. So I had three months with
one old lens and one new one - qhite interesting!
As soon as I came out of the op theatre, even though my sight
through the new lens was initially blurred, the difference in color was
amazing (it is the first thing most who have lens replacements comment on
apparently). The nurses shirts were blue instead of a gray-blue, a cyan
poster on the wall was blue, the sky was much bluer than with my old eye,
and a pink skirt that looked quite a nice color with my old eye was quite
lurid with the new one!
Next day the blurring had gone, and I could now see things on the horizon as
sharp as I ever could, and having just walked aroung our village, it's like
one eye is seeing things in 5000K and the other in 6500K. Using both
together seemed to use an intermediate 'WB' at first, although later the new
lens began to dominate.
I tried a rough measurement of the difference in my eyes using Photokit
Color in CS2, and the difference was something like a .15CC yellow filter.
As yellowing affects all those over about 50 yrs, there are an awful lot of
people out there in the world who don't see as much blue as they did when
they were young.
So perhaps publishers of color management books should issue buyers with a
set of blue graduated filters. If you are 50-60 view the pictures with
filter 1, 60-70 use filter 2, 70-80 use filter 3. ;)
To end with, here is a nice quote from an essay on tetrachromacy -
"A recent paper by Kimberly Jameson, Susan Highnote and Linda Wasserman of
the University of California, San Diego, concerning females who may have
tetrachromacy shows amazing results. Up to 50 per cent of women are
tetrachromatic and can use their extra pigments in "contextually rich
viewing circumstances". For example when looking at a rainbow, tetrachromat
females can segment it into, on average, 10 different colours, whereas their
trichromat brothers and sisters can see only seven, much as Isaac Newton's
red, orange, yellow, green, blue, indigo and violet. Consequently for those
special tetrachromat women, this island that they inhabit may be seen in
emerald, jade, verdant, olive, lime, bottle and 34 other shades of green.
Apparently, men and women do see the world differently."
http://www.science-writer.co.uk/award_winners/16-19_years/2004/winner.html
'Normal' human vision? 'Standard Observer'? Most of us are different!!
Bob Frost.
----- Original Message -----
From: "Mark Rice" <email@hidden>
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