// undefined.
type PalettedImage interface {
	// ColorIndexAt returns the palette index of the pixel at (x, y).
	ColorIndexAt(x, y int) uint8
	Image
}

// pixelBufferLength returns the length of the []uint8 typed Pix slice field
// for the NewXxx functions. Conceptually, this is just (bpp * width * height),
// but this function panics if at least one of those is negative or if the