From Andrew Somers, a great primer on how color vision works and how illuminated display technology maps perception to luminance contrast, color gamut, etc. Especially useful is his writeup of not only WCAG 2’s limitations for determining proper contrast for meeting accessibility needs but also the upcoming standards like APAC (Accessible Perceptual Contrast Algorithm) that will pave the way for more useful and relevant a11y standards.
Notes about eyes
If you’re super nerdy and experienced with using Photoshop’s individual color channels to make enhancements or custom masks, you might have noticed that the blue channel has very little influence on the overall sharpness of an RGB image — it never occurred to me that this is inherently a function of our own human eyesight, which is unable to properly focus on blue light, in comparison to other wavelengths!
I like how the paper from the Journal of Optometry that this article links to straight up dunks on our questionably-designed eyeballs:
In conclusion, the optical system of the eye seems to combine smart design principles with outstanding flaws. […] The corneal ellipsoid shows a superb optical quality on axis, but in addition to astigmatism, it is misaligned, deformed and displaced with respect to the pupil. All these “flaws” do contribute to deteriorate the final optical quality of the cornea. Somehow, there could have been an opportunity (in the evolution) to have much better quality, but this was irreparably lost.
This also made me wonder if this blue-blurriness has anything to do with the theory that cultures around the world and through history tend to develop words for colors in a specific order, with words for “blue” appearing relatively late in a language’s development. Evidently that’s likely so, because hard-to-distinguish colors take longer to identify and classify, even for test subjects who have existing words for them!
Research continues on whether humans (and other animals) have the ability to perceive magnetic fields:
Many birds have a compass in their eyes. Their retinas are loaded with a protein called cryptochrome, which is sensitive to the Earth’s magnetic fields. It’s possible that the birds can literally see these fields, overlaid on top of their normal vision. This remarkable sense allows them to keep their bearings when no other landmarks are visible.
But cryptochrome isn’t unique to birds – it’s an ancient protein with versions in all branches of life. In most cases, these proteins control daily rhythms. Humans, for example, have two cryptochromes – CRY1 and CRY2 – which help to control our body clocks. But Lauren Foley from the University of Massachusetts Medical School has found that CRY2 can double as a magnetic sensor.
Vision is amazing, even more so when you take into account the myriad other things that animals and insects can detect beyond just our “visible” EMF spectrum. See also: box jellyfish with their surprisingly complex (and human-like) set of 24 eyes.
Phil Plait of Bad Astronomy lucidly explains display resolution, clearing up arguments about the iPhone 4’s retinal display technology:
Imagine you see a vehicle coming toward you on the highway from miles away. Is it a motorcycle with one headlight, or a car with two? As the vehicle approaches, the light splits into two, and you see it’s the headlights from a car. But when it was miles away, your eye couldn’t tell if it was one light or two. That’s because at that distance your eye couldn’t resolve the two headlights into two distinct sources of light.
The ability to see two sources very close together is called resolution.
DPI issues aside, the name “retinal display” is awfully confusing given that there’s similar terminology already in use for virtual retinal displays…
For those of you with eyes that aren’t easily categorized as simply “brown”, “blue”, or “hazel”: researchers have written up a new genetic model for human eye color phenotyping, published in PLoS Genetics.
We measured human eye color to hue and saturation values from high-resolution, digital, full-eye photographs of several thousand Dutch Europeans. This quantitative approach, which is extremely cost-effective, portable, and time efficient, revealed that human eye color varies along more dimensions than the one represented by the blue-green-brown categories studied previously. Our work represents the first genome-wide study of quantitative human eye color. We clearly identified 3 new loci, LYST, 17q25.3, TTC3/DSCR9, in contributing to the natural and subtle eye color variation along multiple dimensions, providing new leads towards a more detailed understanding of the genetic basis of human eye color.