HSV, HLS and HS

are three variants of what is effectively the same colour space.

They all are effectively the RGB space twisted so that the neutral diagonal becomes the lightness axis, the saturation the distance from the central lightness axis and the hue the position around the center. The only difference between these models is the measurement of saturation, or the strength of the colour.

In HSV, created in 1978 by Alvey Ray Smith, saturation had a maximum on 0 when lightness was zero and 1 when lightness was 1. This is somewhat odd and anti-intuitive when the strength of the colour of white is considered. HLS is much more intuitive. The saturation peaks at a lightness of 0.5 and has a maximum of zero at black and white. The HSI colour space is in fact identical to HLS under a different name.

figure167

Figure: The RGB derived colour spaces (a) HSV, (b) HLS and (c) the most commonly used HSV space.

The most commonly used one, confusingly also called HSV, is a combination and variation on HSV and HLS, appearing to be a simple cylinder. This was done to have a uniform saturation limit. There are the same anomalies at white and black with saturation as with the original HSV. Whenever HSV is referred to in this report it will be to this colour space.

HSV is almost identical to RGB, slightly warped for symmetry's and simplicity's sake. It has made no attempts whatsoever towards perceptual uniformity but has achieved more intuitive dimensions.

 

Extract from : Matthew A Seaborn : http://www.brunel.ac.uk/~eepgmas/report/node26.html