sRGYB for tetrachromates

It is well known and documented that some women, as many as 10%, are tetrachromates. Implications are simple: while most people can distinguish only three different colors and their variations, tetrachromates can distinguish four colors and their variations, enabling them to see up many more colors, theoretically even 200 time more.

Human eye contains two kinds of photoreceptors, named cones and rods. Usually, a human’s eye has about 5,5 million of photoreceptor cones, limiting the eye’s resolution to a theoretical limit of 5,5 Megapixels, or about 11 Megapixels in stereo. They react to more intensive light, making them less usable with darkness. The 120 million or so rods in the human eye do not provide for additional 120 megapixels, since these photoreceptors react to light very slowly and in huge bulk groups. Rods are usable in dim environment, where low intensity is unable to activate any cones. They are of the same colors: blue. This is why all colors at night are shades of blue, and if you see other colors then blue, that just means that it’s not really that dark, and that some cones are being activated.

Usually, a human being has photoreceptor cones of three different colors: Red, Green and Blue. Different combinations of these colors enable the eye to differentiate between about 10 million colors, meaning that distinguishing ability is about 2153. This is not counting special effects like alphas, which do not really create additional colors, but enable us to perceive additional variations, like reflections and refractions. But tetrachromates have and additional receptor color: orange. So comparing to the standard vision of a trichromate, a tetrachromate can distinguish up to 2154 color variations, over two billion. In practice this has been estimated to about 100 million different colors, the lower number resulting from close spectral relation of the additional photoreceptor color (orange-ish) to red and green photoreceptors. This does not mean that tetrachromates see new colors, only that they see more shades.

With continuous push of high definition technologies to mass market, advanced technology is readily available to consumers. More and more consumer displays have native 10-bit panels, enabling them to display about one billion color variations throughout the spectrum. The numbers aren’t very compatible though, because billion colors in sRGB gamut does not cover all 100 million practically perceived variations in RGYB gamut, because in the latter simply many more variations are created in the 590nm wavelength range, while in RGB color distribution is even, regardless of eye color sensitivity.

To satisfy the needs of tetrachromates there are two options: either define a standardized RGYB color space, something like sRGYB, or push for more sensitive reproduction and recording technologies. Simply reproducing a deeper color space does not bring too many advantages, if the source is of low definition. Sure, the upscaling result on the higher precision screens will look better due to higher sub pixel sampling, but the improvement is not really that noticeable. Defining a new colorspace for displays and cameras is quite unreal at this stage, but creating 12- or 16-bit sources and panels is a much more realistic feat.

—EDIT  on OCT 2010—

SHARP was the first commercial entity to offer mass produced consumer goods using described ideology. The product is codenamed Quattron.

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