

Your eyes suck at blue (neat image compression trick) - yummyfajitas
http://nfg.2y.net/games/ntsc/visual.shtm

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ilamont
The page is not loading some images, and loads others very slowly, which makes
it difficult to see the phenomenon described in the post.

Might want to bookmark this and check it out later, after the HN traffic surge
has died down.

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thamer
Cached version: <http://nfg.2y.net.nyud.net:8090/games/ntsc/visual.shtm>

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indiv
In more detail: <http://en.wikipedia.org/wiki/Chroma_subsampling>

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lbrandy
The inherent assumption on which chroma sub-sampling is founded is that
luminance information is far more important than chromanance information. This
is backed up by empirical evidence. From there, the effect follows directly
from the equation for luminance:

Y = 0.2126 R + 0.7152 G + 0.0722 B

From here you can see that green is by far the most important color, followed
by red, and then finally, way down there, blue.

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jobenjo
Umm... I feel like there's a huge flaw in this. He's looking at the different
_channels_ in this image, but couldn't that mean there's just less blue data
in that particular image?

I believe that humans may be worse at seeing blue, but this test seems bogus.
By looking at the channels, he's actually cutting out different subsections of
data, so it's apples to oranges, right? What if there's just much less blue in
this particular photo?

Or am I mistaken?

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mdd
No, You're spot on.

The author states that this is "an unmodified picture, straight off the
digicam". Unfortunately for his test, this means the light passed through a
Bayer filter, which uses a pattern of "50% green, 25% red and 25% blue":
<http://en.wikipedia.org/wiki/Bayer_filter>

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davepeck
Interesting. Until reading this, I never stopped to wonder why OpenGL, for
example, has GL_UNSIGNED_SHORT_5_6_5 (5 bits for red and blue; six for green)
as opposed to some other allocation of 16 bits.

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ijnuhv
Wow - green, the middle of the visual spectrum matters most. If only they had
discovered this years ago there could have been some really good systems for
sending color information by just doing intensity-red and intensity-blue. Or
Y-U + Y-V = YUV if you prefer.

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Aron
I would have started by reducing the bit depth of blue, rather than pixel
width.

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Daniel_Newby
Ah, but the blue receptors in your eye are as accurate as the green ones, just
less tightly packed. Spatial filtering therefore preserves more-visible color
accuracy at the expense of less-visible blue location.

Not that that stops all those standards that use reduced bit depth for red and
blue.

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rfurmani
That makes a lot of sense. When we lived in the wild discerning different
shades of green would have been crucial. It is also known that women can see
more shades of red, probably in order to be able to more effectively gather
edible berries. Now blue, who needs it? ;-)

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Avshalom
No, sorry that's just nonsense.

We're less sensitive to blue light because there is less blue light.

The black body spectrum of the sun peaks at green (which is why plants are
green) and tails of into red. Blue light is not only a proportionately small
section of the energy output but blue photons have more energy per particle
and so there are even fewer photons necessary to make up that section.

That said while I've heard the women have better red resolution that doesn't
necessarily mean they're more sensitive to the color number one. and number
two explanations like "so they could gather berries" tend to come from a
desire to see women barefoot and pregnant rather than solid science.

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tesseract
> The black body spectrum of the sun peaks at green (which is why plants are
> green)

Plants are green because they reflect green light, i.e. they do not absorb it
and use it to facilitate photosynthesis. Chlorophylls tend to have absorption
peaks in the red and blue, which are (in the grand scheme of the
electromagnetic spectrum) near the sun's blackbody peak but do not coincide
with it.

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jballanc
To prevent overheating and excessive evaporation, of course...

