This article is neat about the engineering/marketing (seriously, it’s clear and direct and has useful pictures; that part is highly recommended). The part about vision and color is pretty sloppy though.

This sentence:

> “The reason this trick works is that rods are 20x as dense as cones in the retina, meaning the eye has approximately sqrt(20)=4.5x the spatial resolution in detecting intensity or luminance transitions compared to detecting color or chrominance transitions.”

... is simply false. The reason that we see lightness differences with better spatial resolution has (almost) nothing to do with numbers of rods vs. cones (indeed rods are almost absent from the fovea – the center of the retina – which we use for fine detail perception, basically the opposite of what was claimed), but instead happens because the signals from the three types of cone cells are processed into a single (monochromatic) lightness response, which we use for perception of fine detail. The signals from the cone cells are also processed into two color difference signals, but over bigger patches of retina: sort of a neurological analog to the “chroma subsampling” that happens in JPEG compression. In other words, JPEG compression does work because we see fine details monochromatically, but instead of “leveraging” this mostly irrelevant cone/rod difference as claimed, it’s really using the same basic approach (averaging/tossing out color data) that the eye itself uses.

Actually, the next few sentences are somewhere between misleading and wrong, too.

> “The eye is more sensitive to quantization levels of green light than to levels of red or blue light, which is probably related to the fact that the sun emits more power in the green region of the visible spectrum than in red or blue. (The eye's spatial resolution in each of the three primary colors is approximately uniform.)”

The eye is more sensitive to green light because we use three cone receptors with the biggest overlap in sensitivity in the green part of the spectrum, so that when you add up their responses to a signal (in the combined lightness signal I mentioned), green wavelengths have more of an impact.

It certainly has something to do with evolution and the spectra of reflected sunlight, but various animals have different spectral sensitivities, so the causality is complex. The sun emits light over a huge range of wavelengths (far beyond the visible spectrum in both directions), and exactly which part makes it to our eyes depends on time of day, weather conditions, altitude, etc.

The three “primary” colors are somewhere between extremely simplified model, useful engineering approach, and myth. We also have somewhat different spatial sensitivities to the three primaries in a computer display, as far as I know.

> “Also the blue and red subpixels are twice the size of green, making them twice as likely to be illuminated at the perceptual edge of a hard intensity transition than green.”

Let’s see here. 1/3 the total area is green, 1/3 the total area is red, and 1/3 the total area is blue. How is it that edges are twice as likely to fall on red or blue than green, again? (In other words, there’s some difference because of the different pixel sizes, but whatever is meant here is being poorly explained, and important assumptions about the edges in question are left unstated.)

Vision is complicated, and there’s a lot of heavy math going on in the neurons in your retina, before signals ever get transmitted through the optic nerve. It depends on adaptation to current light level and color, on what size blobs you’re looking at, on the surrounding colors, and on inferences about objects and how they’re lit. These complexities lead to all those famous optical illusions. So it’s worth using simplified models, to cut out complexity incidental to whatever you’re trying to explain. But that doesn’t give license to just make up stuff.

For anyone interested, this is a good place to start:

http://www.handprint.com/HP/WCL/color1.html

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One last thing. I’m pretty suspicious of this:

> “Overall, it is hard to see any really good advantages to the PenTile layout.”

Presumably the engineers who designed the thing had some compelling reasons. (It’s conceivable that it was driven by a desire to make a worse display that could be better hyped by marketing, but that seems extremely unlikely to me; I’m suspicious.) I’d like to hear what those are instead of just a hand-wavey “I don’t know what they are so I’m going to imply there are none”.