How to tell visible color from RGB values

Question

I'm working an image analyzation project that checks the rgb values at set locations in a host of images, and need to be able to know if a certain area is green or blue. Originally I thought I could do this by testing if g>b in the rgb, but I've come to realize that often there can be more blue than green in a green image, due to the mixture with red. How can I tell- possibly a formula or an algorithm, what a color visibly appears to be based on the rgb?

Answer 1

You can convert RGB values to HSB values using the Color classes RGBtoHSB method. The resulting hue value falls between 0-1, with the hue value of green (0,255,0) at 0.33 and blue (0,0,255) at 0.66

float[] hsb = Color.RGBtoHSB(0, 255, 0, null);//green
System.out.println(hsb[0]);
hsb = Color.RGBtoHSB(0, 0, 255, null);//blue
System.out.println(hsb[0]);

From this you could create a metric for hue values 'closer' to green, for instance any hue value < 0.5 is more green than blue.

Below is an image depicting how the colors change in this color space, with hue on the X axis (note in this picture hue varies from 0-360 degrees, whereas the RGBtoHSB returns values 0-1)