Rg chromaticity

The RG chromaticity of the normalized RGB space

is a chromaticity space, a two-dimensional color space in which there is no intensity information.

In the RGB color space, a pixel is identified by the intensity of red, green, and blue primary colors. Therefore, a bright red can be represented as (R,G,B) (255,0,0), while a dark red may be (40,0,0). In the normalized RGB space or RG space, a color is represented by the proportion of red, green, and blue in the color, rather than by the intensity of each. Since these proportions must always add up to a total of 1, we are able to quote just the red and green proportions of the color, and can calculate the blue value if necessary.

Conversion between RGB and RG Chromaticity

Given a color (R,G,B) where R, G, B = linear intensity of red, green and blue, this can be converted to color

(

r

,

g

,

b

)

{\displaystyle (r,g,b)}

where

r

,

g

,

b

{\displaystyle r,g,b}

imply the proportion of red, green and blue in the original color:

The sum of rgb will always equal one, because of this property the b dimension can be thrown away without causing any loss in information. The reverse conversion is not possible with only two dimensions, as the intensity information is lost during the conversion to rg chromaticity, e.g. (1/3, 1/3, 1/3) has equal proportions of each color, but it is not possible to determine whether this corresponds to black, gray, or white. If R, G, B, is normalized to r, g, G color space the conversion can be computed by the following:

The conversion from rgG to RGB, is the same as the conversion from xyY to XYZ. The conversion requires at least some information relative to the intensity of the scene. For this reason if the G is preserved then the inverse is possible.