This function modifies a given image in order to keep a specific hue (given too) and to desaturate the rest of the image. This procedure originates an image with black and white colormap, excluding the parts colored with that hue. Input and output parameters are specificated in the function header.
Example of use extracting the blue hue (H: 150º - 270º):
I = imread('myimage.jpg');
I = im2double(I);
I_m = colorfilter(I,[150 270]);
imshow(I_m,[]);