goutil/image/color/color.go

package ucolor

import "image/color"

// Transparent returns whether or not a color has transparency.
func Transparent (c color.Color) bool {
	_, _, _, a := c.RGBA()
	return a != 0xFFFF
}

// ToRGBA converts any color to a color.RGBA value.
func ToRGBA (c color.Color) color.RGBA {
	r, g, b, a := c.RGBA()
	return color.RGBA {
		uint8(r >> 8),
		uint8(g >> 8),
		uint8(b >> 8),
		uint8(a >> 8),
	}
}

// Premultiply applies alpha-premultiplication that colors must apply as per
// color.Color.RGBA. This is an intrinsically lossy proccess.
func Premultiply (ur, ug, ub, ua uint32) (r, g, b, a uint32) {
	return (ur * a) / 0xFFFF,
		(ug * a) / 0xFFFF,
		(ub * a) / 0xFFFF,
		ua
}

// Unpremultiply reverses alpha-premultiplication that colors must apply as per
// color.Color.RGBA. This may or may not return the precise original color.
func Unpremultiply (r, g, b, a uint32) (ur, ug, ub, ua uint32) {
	return (r / a) * 0xFFFF,
		(g / a) * 0xFFFF,
		(b / a) * 0xFFFF,
		a
}