Returns the index of the color in the palette of the image which is "closest" to the specified RGB value.
The "distance" between the desired color and each color in the palette is calculated as if the RGB values represented points in three-dimensional space.
If you created the image from a file, only colors used in the image are resolved. Colors present only in the pallete are not resolved.
An image resource, returned by one of the image creation functions, such as imagecreatetruecolor().
Value of red component
Value of green component
Value of blue component
Returns the index of the closest color, in the palette of the image, to the specified one