Color Channels

Most computer applications specify color in three-component systems such as RGB (Red, Green, Blue), HLS (Hue, Luminance, Saturation), or HSV (Hue, Saturation, Value). Bersoft Image Measurement can perform statistical methods on RGB and HSV channels (see Array/Band Analyzer, Statistics and Pixel profile), and adjust HSV channels as well (See Channels window).

This images have a single 8 bits channel, allowing representing 256 gradations of gray. A 0 value represents the black color and 255 is pure white.

The RGB model, one of the Additive Color models, is used on computer monitors. It has three primary colors: red, green, and blue, that it creates by emitting light. These three colors are combined in various proportions to produce all the colors displayed on your screen. They are referred to as additive because they combine to produce white.

Primary colors are measured as a value from 0 to 255. The colors produced by combining the three primaries are a result of the relative value of each primary. An absence of the three primaries colors, all three values of 0, results in black; when all three have values of 255, they produce white.

Graphic applications for the PC (Personal Computer) usually employ this color space because this model maps well to the way the common Cathode Ray Tube (CRT) display works.

When luminance is computed from red, green and blue, the coefficients will be a function of the particular red, green and blue spectral weighting functions employed, but the green coefficient will be quite large, the red will have an intermediate value, and the blue coefficient will be the smallest of the three.

The coefficients that Bersoft Image Measurement uses to compute luminance from linear red, green and blue are these:

The coefficients 0.299, 0.587 and 0.114 properly computed luminance for monitors having phosphors that were contemporary at the introduction of NTSC television in 1953, however, these coefficients do not accurately compute luminance for contemporary monitors.

Hue is the attribute of a visual sensation according to which an area appears to be similar to one of the perceived colors, red, yellow, green and blue, or a combination of two of them.

Saturation is the colorfulness of an area judged in proportion to its brightness. Saturation runs from neutral gray through pastel to saturated colors. A vivid color usually has a high saturation level (not much gray). As the saturation decreases, the amount of gray increases, and the color becomes less vivid.

The Hue Channel is shown from 0 to 359 degrees (0º = 360º = Red); both Saturation and Value channels are shown in gray scale from 0% to 100%.

RGB Color space equivalence to HSV Channels
		HSV Channels values			RGB Channels values
	Color	Hue Degree	Saturation %	Value %	Red	Green	Blue
	Red	0º = 360º	100	100	255	0	0
	Yellow	60º	100	100	255	255	0
	Green	120º	100	100	0	255	0
	Cyan	180º	100	100	0	255	255
	Blue	240º	100	100	0	0	255
	Magenta	300º	100	100	255	0	255

HSL and HSV are quite similar color spaces. Actually they are the different forms of HSV cylindrical space. The difference is that in HSV space to get white color you should set Saturation to "0". But in HSL space at L=1 you get white regardless the saturation value.