The horseshoe: the visual version
Every widget from the article Why the map of visible color is a horseshoe, in one place, for when you would rather play than read. Under each heading is a short note on what that widget illustrates. Two of them are bigger versions of the article's charts, with more to play with.
- Three kinds of cones in the eye
- The map and what can show a point
- Drawing the horseshoe
- From xy to u′v′
- Dragging your own primaries
Three kinds of cones in the eye
The retina of an average human eye has three kinds of light-sensitive cells, called cones. The curves show how strongly each kind reacts to a single wavelength. The L and M curves overlap a lot, so no light can wake up only one of them. That overlap is why the edge of the horseshoe is curved.
The map and what can show a point
The chromaticity map with x across and y up. Hover or tap a point, or use the x and y sliders, and it tells you which color spaces can show it.
Drawing the horseshoe
Slide through the wavelengths and watch the curve get drawn from the cone responses. The horseshoe is what you can mix from one pure light for every wavelength.
From xy to u′v′
The same colors on the xy chart and on u′v′, a later chart designed so equal distances look more equal. Slide between the two to see the shape change.
Dragging your own primaries
Drag three to six primaries around and watch how much of the visible color they cover. Three well-placed lights already cover most of it, a fourth adds a lot, and after that the gains get small.
For the story behind each chart, read the full article.