(PHP 4 >= 4.0.6, PHP 5)
imagecolorclosestalpha -- Get the index of the closest color to the specified color + alphaReturns the index of the color in the palette of the image which is "closest" to the specified RGB value and alpha level.
Nota: Esta funcion requiere GD 2.0.1 o posterior.
See also imagecolorexactalpha().