[ajenner]

The programmatic transitions between still images use linear RGB space, which is the correct way to interpolate between two colours. The maths behind it is pretty simple - essentially just reversing the gamma correction from normal (0-255) sRGB space before the interpolation and redoing it for the final colour (no need to get into the hairy areas of LAB or perceptual colour spaces for this). Once we know the colour we want, we choose the character (from a list of 6) and attribute which most closely matches that colour. Of course, it's all done using lots of lookup tables so that we can process several hundred character cells per frame.

[jart]

My point is that sRGB linear interpolation does not accurately model the blending of color that happens in nature, which is something that should happen with CP-437 shade blocks. Here's a web page I set up so you can see for yourself. https://justine.lol/color.html Even within the context of sRGB itself, it's not "correct" at all. For example, yellow and blue should make pink. But sRGB predicts it as being grey. Depending on how good your monitor is, the shade blocks should make pink, but even that is usually thwarted somewhat by subpixel layout. For example, if you drag the window around on an LCD, the coloring of the shade blocks will change weirdly as subpixels move. Subpixel layout shouldn't be an issue with IBM-PC CRT monitors. I wish I had one to confirm what it does. But in general this is just one of the weaknesses of the sRGB colorspace. But if you use something like CIELAB then it does predict pink. But that space has weaknesses of its own. But those problems are nowhere near as challenging as shade blocks, because linear interpolation just chooses a new color and doesn't need to predict anything. To choose colors for shade blocks you're applying your model to predict a more natural phenomenon.

[ajenner]

There's a difference between linear interpolation of sRGB values (what you're doing on your page) and linear interpolation of linear RGB values (which gives better results). This is the explanation that made it all fall into place for me: http://www.ericbrasseur.org/gamma.html?i=1 . The linear RGB colour space is also a linear transformation of the CIELAB space so doing the interpolation in this space is equivalent to transforming to CIELAB space, doing the interpolation there, and then transforming back.

However, for the purposes of Area 5150 I think the differences between sRGB interpolation and linear RGB interpolation would have been too subtle to notice since there are only 6 * 16 * 16 = 1536 dithered colour/pattern combinations to choose from in the first place - the error introduced by that quantisation is likely larger than the sRGB vs. linear RGB difference. But I used linear RGB anyway, just to be correct about it.