rg chromaticity
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.
imply the proportion of red, green and blue in the original color:[2] [3]
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:
[4] The conversion requires at least some information relative to the intensity of the scene.
Computer vision algorithms tend to suffer from varying imaging conditions.
One common problem in computer vision is varying light source (color and intensity) between multiple images and within a single image.
[5] The rg colorspace is used out of a desire for pixel-based photometric invariance.
Where color is being used to track an object in an RGB image, this can cause problems.
In practice, computer vision uses an "incorrect" form of rg colorspace derived directly from gamma-corrected RGB, typically sRGB.
As a result, full removal of intensity is not achieved and 3D objects still show some of fringing.
A neutral object infers equal values of red, green and blue stimulus.
The lack of luminance information in rg prevents having more than 1 neutral point where all three coordinates are of equal value.
The white point has one third red, one third green and the final third blue.
On an rg chromaticity diagram the first quadrant where all values of r and g are positive forms a right triangle.
[6] Therefore, a white with equi-energy lights of 1.000 + 4.5907 + 0.0601 = 5.6508 lm can be matched by mixing together R, G and B.
Guild and Wright used 17 subjects to determine RGB color matching functions.
[7] RGB color matching serve as the base for rg chromaticity.
Normalized RGB tristimulus value can be plotted on an rg chromaticity diagram.
The test light is also to bright to account for this reference stimuli is added to the target to dull the saturation.
calls for color matching functions that are negative at certain wavelengths.
color matching function appears to have negative tristimulus values.
The figure to the side is a plotted rg chromaticity diagram.
Noting the importance of the E which is defined as the white point where rg are equal and have a value of 1/3.
Any point on the line represents the limit in rg, and can be defined by a point that has no b information and formed by some combination of r and g. Moving of the linear line towards E represents a decrease in r and g and an increase in b.
But when trying to form color matches using real stimuli negative values are needed according to Grassmann's Laws to match all possible colors.
This is why the rg chromaticity diagram extends in the negative r direction.
Avoiding negative color coordinate values prompted the change from to rg to xy.
On an xy chromaticity diagram the spectral locus if formed by all positive values of x and y.
