The RGB color space is based on the use of the red, green, and blue additive primary colors. We saw in the first recipe of this chapter that these primaries have been chosen because they can produce a good range of colors well aligned with the human visual system. It is often the default color space in digital imagery because this is the way color images are acquired, that is, through the use of red, green, and blue filters. Additionally, the red, green, and blue channels are normalized such that when combined in equal amounts, a gray-level intensity is obtained, that is, from black (0,0,0) to white (255,255,255).
Unfortunately, computing the distance between the colors using the RGB color space is not the best way to measure the similarity between two given colors. Indeed, RGB is not a perceptually uniform color space. This means that two colors at a given distance might look very similar, while two other colors separated by the same distance might look very...