(PHP 4 >= 4.0.6, PHP 5)
imagecolorclosestalpha -- Get the index of the closest color to the specified color + alpha
Returns the index of the color in the palette of the image which
is "closest" to the specified RGB value and
alpha level.
imageAn image resource, returned by one of the image creation functions, such as imagecreatetruecolor().
redValue of red component
greenValue of green component
blueValue of blue component
alphaA value between 0 and 127. 0 indicates completely opaque while 127 indicates completely transparent.