We have encountered two problems in this step that have been solved in a pre-processing phase. The first
one is that human skin hue values are very near to red colour, that is, their value is very close to 2π radians,
so it is difficult to learn the distribution due to the hue angular nature that can produce samples on both
limits. To solve this inconvenience the hue values are rotated π radians. The second problem in using HSL-space is when the saturation values are close to 0, because then the hue is unstable and can cause false
detections. This can be avoided discarding saturation values near 0.