Hue and saturation, Computer Graphics

Hue and Saturation: A light source produced by a sun or electric bulb emits all frequencies within the visible range to give white light. When this light is incident upon an object, some frequencies are absorbed and some are reflected by the object. The combination of reflected frequencies decide the color of the object. If the lower frequencies are predominant in the reflected frequencies, the object color is red. In this case, we can say that the perceived light has a dominant frequency at the red end of the spectrum, therefore, the dominant frequency decides the color of the object. Due to this reason dominant frequency is also called hue or simply the color. Apart from the frequency there are two more properties which describe various characteristics of light. These are brightness and saturation (purity). The saturation describes the purity of the color. Conversion Between HSV And RGB Models It HSV color parameters are made available to a user of a graphics package, these parameter are transformed to the RGB settings needed for the color monitor. To determine the operations needed in this transformation, we first consider how the HSV hex cone can be derived from the RGB cube. The diagonal of this cube from black (the origin) to white corresponds to the v axis of the hex cone. Also, each sub cube of the RGB cube corresponds to a hexagonal cross- sectional area of the hexatone. At any cross section, all sides of the hexagon and all radial lines from the V axis to any vertex have the value V. For any set of RGB values, V is equal to the maximum values in this set. The HSV point corresponding to the set of RGB values lies on the hexagonal cross section at value V. Parameters S is then determined as the relative distance of this point from the V axis. Parameter H is determined by calculating the relative position of the point within each sextant of the hexagon. An algorithm for mapping any set of RGB values into the corresponding HSV values is in the following procedure. We obtain the transformation from HSV parameters to RGB parameters by determining the inverse of the equations in RGB To HSV procedure. These inverse operations are carried out for each sextant of the hex cone. The resulting transformation equations are summarized in the following algorithm. 

 

 

Posted Date: 7/12/2012 6:46:41 AM | Location : United States







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