What is HSI color space?
For most practical machine vision purposes, HSI may be regarded as the same space as RGB but represented in a different coordinate system. This diagram shows how the RGB cube would appear viewed from the black end, looking in the direction of the black-white diagonal. The HSI coordinate system is cylindrical with the intensity (I) axis coinciding with the black-white diagonal of the RGB system. Saturation (S) is the radius from the intensity axis and hue (H) is the angle with respect to (usually) the red direction. When we assign a single name to a color it is usually the hue to which we refer. A number of slightly different representations of the exact transformation between HSI and RGB are in common use.
