Comment by jart

It is hard. Anyone can mix colors by hand in an ANSI art editor. However this demo is huge and certainly appears to be programmatically generated at times. It's very hard to program a computer to blend colors using CP-437 shade blocks, because you're not actually linearly interpolating two RGB values like you would normally in graphics programming. The blending happens in physical space, hence physics. Read the section about gradients in the link you provided. They say they tuned the gradients, but they didn't explain how they did it. For example, was it just spending countless hours eyeballing color combinations until it looked nice? Or did they use a formula like CIELAB ΔE* to predict how background / foreground / shade block combinations would be perceived? https://en.wikipedia.org/wiki/Color_difference#CIELAB_%CE%94...* Those formulas are much more complicated than the RGB((r2-r1)/2,(g2-g1)/2,(b2-b1)/2) blending that computers use in software (which just punts the problem to the chosen color space). Notice also how CIE needed to keep revising the formulas over the decades since color isn't something we entirely understand yet.