Returns the index of the color of the pixel at the
specified location in the image specified by image.
If PHP is compiled against GD library 2.0 or higher and
the image is a truecolor image, this function returns the RGB
value of that pixel as integer. Use bitshifting and masking
to access the distinct red, green and blue component
values:
See also imagecolorset() and
imagecolorsforindex().