The HSY color model is similar to the well-known HLS model – the H and S channels for a given color have equal values in both models. However, the HSY model has a notable advantage: its lightness (Y) channel takes human perception of color into account. The human eye senses different colors as having different brightness: for example, pure orange, yellow and green are generally perceived as brighter than pure red, violet and blue. This is reflected in their respective values of the Y channel: pure green will have higher Y value than pure red. An obvious use of the HSY color model is perception-based conversion of color photos into black-and-white. For more information on the HSY color model, see The Taming of the Hue, Saturation and Brightness Colour Space publication by Allan Hanbury.
Filter Forge uses the HSY color model in the Desaturate component (Weighted Average method), in the Blend component (Hue, Saturation, Color and Luminosity modes) and in all components that have the Preserve Color option.
