Remember ye olde dayes when we had to be mindful of the so-called “web safe palette“? Once upon a time, screens could display 24-bits colors, but only 256 at a time in some “hi-res” modes. But that’s not what I’m going to tell you about: I’d rather tell you about the encoding of the palette, and about a somewhat better palette. And also about using fractions of bits for more efficient encodings.
Pairing functions are fun. Last week, we had a look at the Cantor/Hopcroft and Ullman function, and this week, we’ll have a look at the Rosenberg-Strong function—and we’ll modify it a bit.
Pairing functions are used to reversibly map a pair of number onto a single number—think of a number-theoretical version of std::pair. Cantor was the first (or so I think) to propose one such function. His goal wasn’t data compression but to show that there are as many rationals as natural numbers.
Cantor’s function associates pairs (i,j) with a single number:
…but that’s not the only way of doing this. A much more fun—and spatially coherent—is the boustrophedonic pairing function.
HSV (hue, saturation, value) and HSL (hue, saturation, lightness) are two intuitive, but computationally cumbersome, colorspaces.
The basic idea behind these colorspaces is the good ol’ color wheel, where primary colors are placed on a triangle and secondary colors between; complementary colors are to be found opposite on the circle. That’s intuitive enough, but we still have to make it into a workable colorspace.
Let’s have a look at another physical colorspace: Pantone.
The Pantone color system isn’t particularly useful for us as it is mainly concerned with “real world” colors, as in print. It also uses a variety of special dies, for metallic or fluorescent finish. It does, however, allow very accurate and consistent color reproduction for packaging, posters, and comics.
While the RGB and its transformed colorspaces are useful for computer graphics and video compression, there are other colorspaces that deal with “real life” materials, like ink and paint. Albert Henry Munsell (1858–1918), a painter, proposed such a system.
Unlike RGB and its friends, the Munsell colorspace isn’t based on mixing three primaries, but rather on hue (tint), value (brightness) and chroma (density of color, or saturation), and colors are arranged on a color wheel, but unlike the usual three/six primary color wheel, Munsell’s has 5 primary colors .