Find xterm-256color approximations of RRGGBB triples
This is a minimally-engineered PHP script for finding a "close" color from the
xterm-256color palette, given a hex triple like #a0df00.
I used it to build the first pass at the 256-color mode for zora-theme-vim. There were a couple of manual tweaks required, but overall, it worked wonders.
The "closest" color is found by converting to HSL, then finding the color in the palette with the lowest total error value. Error values are tuned based on gut feeling and hand-weighting, to push the result to a close lightness, allowing less accuracy in hue and even less in saturation.
Then, there's an extra error factored in when comparing a palette gray to a non-gray target color. This prevents the lenience in saturation from turning everything to gray.
I wanted to try L*C*h, but to use the formulae I found, I'd have to convert RGB to XYZ to L*a*b* to L*C*h to get there.
This is a weekend hack. I went with HSL.
MIT.