Very interesting, but I had a question about the background color on the page. but first some ... background. A long time ago, I worked at a digital printer manufacturer and I was building a equal perceptual gradient target for a backlit transparency material, Ilfochrome, at a customer site. One thing I found interesting was how much the perception of how 'linear' the gradient looked depended on how bright the background was.

A 'target' was a set of densities we would calibrate the machine to reach for a particular RGB value. 0,0,0 = 3.4D and 255,255,255 = .04D (for transparent material).

One group in the company insisted on a simple cube root density drop off, based on a reading of the L* formula. However, when the customer printed a large gradient with it, they rejected it. It looked like the 'linear' gradient on your site. However, when we put the test pattern (a small 4x8") pattern on the light board, it looked perfect.

So we tried an experiment, we printed 3 gradients on a full sized sheet, (50 inchesx50 inches), one with a 'clear' background, one with a 50% grey and one with a black background.

I was in the field, so I found a gradient that looked good, but did a bunch of study when I got back, I felt that some of the newer CIE models at the time did take into account background.

Tldr; I was curious is your page and those models included into its gradient calculation what the surround is? Also, it would be interesting to display these with an adjustable background. (dark, light, grey), or with colors.

FYI the + button doesn't work for me on Android Fennec (Firefox) 91.2.0 (Build #912020), though the rest seems to