Returns the index of the color in the palette of the image which is "closest" to the specified RGB value and alpha level.
A GdImage object, returned by one of the image creation functions, such as imagecreatetruecolor.
Value of red component.
Value of green component.
Value of blue component.
A value between 0 and 127. 0 indicates completely opaque while 127 indicates completely transparent.
Returns the index of the closest color in the palette.