
Your eyes suck at blue - siim
http://nfggames.com/games/ntsc/visual.shtm
======
bradleyland
Ugh. We don't have an entirely clear picture of how our eyes physically detect
color, much less how we perceive it, but there are serious problems with the
argument the author makes here. You cannot simply take a color photograph of a
scene, split it in to three channels, then point out that the blue channel is
"dark and contains less detail" as evidence of our inability to perceive the
color blue. The fact is that the blue channel really _is_ darker because of
the actual lack of blue light in the photo.

The trick here is that the areas that have a lot of detail (her face, for
example) contain less blue. If you use a color meter to inspect the areas
around the girls face, you'll find that there is less blue light present. That
makes sense, considering that our skin doesn't contain a lot of blue pigment.
This fact is exacerbated by the fact that the author overlaps the channel
samples in a way that places emphasis on the areas impacted the most.

Basically, the author fails to understand the additive color model. We don't
notice the pixelation of the blue channel in this photo because the result of
the alteration is to introduce a low-contrast color in to the photo where the
aberration overlaps: yellow. If you look closely, you'll see that the areas
where you see cyan and magenta in the red and green channels are replaced by
yellow in the corresponding blue channel alteration. The effects are
diminished by two factors: there isn't much blue luminance present to
influence the other colors, and yellow contrasts poorly with most of the
colors in the photo where we notice it (the hood is white).

If you were to take a color-neutral photograph and split out the RGB channels,
you'd perceive the same level of detail in all channels.

EDIT: I'd kind of like to take back that last statement about perceiving the
same level of detail in all channels. I don't know that you would, but that's
not the primary thing that bugs me about the author's argument. My main point
is that his argument is flawed, not his assertion. I don't know enough about
human color perception to make that argument.

~~~
jemfinch
You're wrong.

No, you can't just split a picture into three channels and say "Hey, blue
looks dark," because blue might actually _be_ dark.

You can, however, make a picture grayscale, then turn that same grayscale
picture into redscale, greenscale, and bluescale. The luminance would be
exactly the same for every pixel, the only difference would be the pixel's
color.

I did that, in fact, and you know what? Your eyes really do suck at blue:
[http://www.flickr.com/photos/jemfinch/sets/72157617048178001...](http://www.flickr.com/photos/jemfinch/sets/72157617048178001/)

We do have a clear enough picture of how our eyes work to know that the blue
receptors are far fewer than the red and green receptors. Your eyes suck at
blue. My eyes suck at blue. All of our eyes suck at blue.

Every time this story comes up, someone brings up this point. That's why I did
it right: so I could reply to arrogant comments like yours that assume because
an experiment is flawed that the theory it tried to prove must be wrong.

~~~
tensor
Actually, your conclusion is incorrect. While there are fewer receptors for
blue, each is much more sensitive. All you demonstrated is that the sRGB color
model is blue deficient. See <http://en.wikipedia.org/wiki/Color_vision> and
[http://www.ecse.rpi.edu/~schubert/Light-Emitting-Diodes-
dot-...](http://www.ecse.rpi.edu/~schubert/Light-Emitting-Diodes-dot-
org/Sample-Chapter.pdf) for details.

In particular, I'd like to draw your attention to the CIE 1931 chromatic
diagram in the wikipedia link. This is supposed to represent the visible
spectrum that the eye can see. The triangle is the sRGB colour space, what
your monitor can reproduce. Notice how little blue the triangle contains? This
is why your blue image looks so dark.

From the second link, it also turns out that CIE 1931 actually underestimates
blue sensitivity. The book chapter discusses a corrected version called CIE
1978. It also has a plot of the eye sensitivity to various wavelengths. It
turns out that our eyes are about as good at both blue and red, but more
sensitive to green and yellow.

Experimentation is difficult. There are often a lot of factors you need to
consider. Also, may I ask that you be a little less confrontational in the
future? It's quite unnecessary. The majority of people here have good
intentions.

edit: upon further research, it turns out it's even more complicated than just
the sensitivity and cone numbers. Here: [http://hyperphysics.phy-
astr.gsu.edu/hbase/vision/rodcone.ht...](http://hyperphysics.phy-
astr.gsu.edu/hbase/vision/rodcone.html#c3b) it states that we should still
have less sensitivity to blue. However, we do perceive it to be the same
intensity despite this. It appears that we do have difficulty determining
details from blue objects, though. The reason is that most of the blue
receptors are on the outer areas of the retina. It is a complex topic
apparently.

~~~
dgreensp
Agreed. If red=255 looks brighter on your monitor than blue=255, well, that's
how the monitor was designed!

------
DrStalker
Does the article mention that images taken with a digital camera (with a few
exceptions) only sample 1/2 the green pixels and 1/4 each of the red and blue
ones?

<http://en.wikipedia.org/wiki/Bayer_filter>

There will be more information in the green channel because that is how the
camera is built. I'm sure somewhere there is proper research that was was used
in developing the Bayer filter that indicates the human eye is more sensitive
to green, but this looks like a case of bad methodology ending up with the
right conclusion through luck.

~~~
jkic47
To add to your point, a typical imager pixel can only sense one color - red,
green or blue (caveat: there are now some imagers that can simultaneously
sense multiple colours). The green value of a non-green pixel is interpolated
from the surrounding pixels capable of sensing green. Thus, only 1/3 of your
RGB image is "real" - the remaining 2/3 is interpolated.

------
rix0r
> This is how DVDs work: a high res green image and two low-res images, one
> for red, one for blue.

Not true. MPEG-2 uses the YCbCr colorspace, consisting of a high resolution
Luminance signal (brightness) and a low resolution Chrominance signal (color).
So in fact, all color information is subsampled, green is not treated
specially.

~~~
kwantam
Green is absolutely treated specially in YCbCr; you just have to understand
how YCbCr relates to RGB.

ITU-R BT.601 defines YCbCr as follows:

    
    
        Y ~= 0.30 R + 0.59 G + 0.11 B
        Cb ~= -0.17 R - 0.33 G + 0.5 B
        Cr ~= 0.5 R - 0.42 G - 0.08 B
    

Y is given the most bandwidth, and green makes up 60% of Y. Cb and Cr are
allocated substantially less bandwidth, and green still makes up a sizable
chunk of the value. In total, green occupies about 2/3 of the bandwidth in
YCbCr. That's pretty much the whole point of doing it---RGB spends an
unnecessary amount of bandwidth on R and B.

(reference: <http://en.wikipedia.org/wiki/YCbCr> )

------
clay
This plays into something that Robin Hanson was doing with colors. Blue = Far
Mode = grainy, picture unclear and far away.
<http://www.overcomingbias.com/2010/05/color-meanings.html>

------
mfukar
I'm wondering how much of this isn't an artifact of that specific picture; how
do we know the RGB distribution in the original pic isn't skewed away from
blue? That might explain why there's little information in the blue channel,
right?

edit: no -> little

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iwr
Low blue sensitivity may be due to the eye's lens being opaque to UV (very
bright blue). This is for good reasons because then daylight illumination
would be painful and cause retinal damage over time.

The blue color receptor can actually capture a wider range blues and low UV
shades. People who had cataract surgery (which replaces the defective lens
with an artificial one) may see into these deeper shades of blue if they
received an older style of implant.

[http://www.guardian.co.uk/science/2002/may/30/medicalscience...](http://www.guardian.co.uk/science/2002/may/30/medicalscience.research)

------
ajg1977
Trivia: DXT compression (the texture compression used in virtually all modern
games) uses a 5:6:5 format for end channels giving the green channel the extra
bit of precision, for exactly this reason.

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olalonde
I wouldn't have thought so given that blue is the favorite color of most
people[1].

[1] <http://www.joehallock.com/edu/COM498/preferences.html>

~~~
icegreentea
Not really. Favourite colours have to do more with social and cultural
features than your ability to finely distinguish between different shades of
said colour. I strongly believe that the proper phrasing for the results
should not be "blue is the favorite color of most people" but rather "blue is
the favourite colour of most White North Americans/Western Europeans".

I bet if this was done in China, it would be more heavily weighted towards
red, and if done in ancient Phenoncia, it would probably be purple.

~~~
mynameishere
I think this is why people like blue.

<http://www.flickr.com/photos/lighthearted/37225804/>

------
jarin
That is pretty neat, although I'm not sure I understand all the outrage. "THE
DVD FORUM IS STEALING OUR PIXELS!!"

If your eye doesn't notice the difference, are you being "bilked"?

~~~
docgnome
I think it's the same situation as so called "audiophiles" who spend large
amounts of money on gold cables and ultra expensive headphones. They may or
may not be able to tell the difference but the knowledge that their 10000USD
headphones produce a slightly large range of sound than the 100USD pair makes
them believe that the more expensive headphones are worth it. In the same way
you could probably sell some sort of... DVD re...bluer? or something and make
a mint even if no one could tell the difference.

~~~
jiganti
I'm not sure it would work if _no one_ could tell the difference, and I'll
cite your example of the audiophiles.

Many people are overpaying for sound equipment that would sound no different
to them than stuff half the price, but the fact that there _are_ people that
can tell the difference, who talk about that difference constantly, keeps the
deluded part of the market in the dark. These people will never do some sort
of double-blind test to identify whether or not they can tell the difference,
but since there were originally people who could recognize it, others started
to follow blindly. There has to be some starting off point before the masses
buy into the hype.

