Overview :

A lot of studies demonstrates that human perception of colours is based upon three qualities: the hue, the luminance and the saturation.

When we speak about a colour, we say “a red (hue) car”, “this is a dark (luminance) green (hue)”, “that violet (hue) is brilliant (saturation)” and not “a 20% green, 10% blue and 50% red car”!

So, when operating with colours, the hls space is the most intuitive, with respect to the rgb (or yuv) one.

This plugin operates principally with parameters expressed in that space: you can work directly on the saturation, the luminance and the hue.

While there's filters who works on luminance (permitting to change the brightness and contrast), the operations related to saturation are simply multiplications.

The filter ExpSat instead permits the specifications of complex math functions, through some intuitive parameter, that will be applied to saturation and luminance:

Expsat

graph mode on

The filter Colorize changes the colour dominance of image, relatively to the user-definable saturation and luminance factors.

The filter HLSnoise (beta) adds a noise to the image, obviously user-definable, separately to the HLS dimensions.

The filters are hue sensitives: you can specify the hue range being excluded by the operations.

Colorize

Graph and test modes on

As you can see in the previous images, filters are equipped by a graph mode, that will display mathematical and statistical informations, and a test mode, useful to calibrate the hue range by having a visual control of image composition.

Brabudu 2006
f.capuzzi@tiscali.it