Function Diff

cmpimg/cmpimg.go:208–238

Diff calculates an intensity-scaled difference between images a and b and places the result in dst, returning the intersection of a, b and dst. It is the responsibility of the caller to construct dst so that it will overlap with a and b. For the purposes of Diff, alpha is not considered. Diff is no

(dst draw.Image, a, b image.Image)

// difference between the input images, but rather to highlight differences
// between them for testing purposes, so the calculation is rather naive.
func Diff(dst draw.Image, a, b image.Image) image.Rectangle {
	rect := dst.Bounds().Intersect(a.Bounds()).Intersect(b.Bounds())

	// Determine greyscale dynamic range.
	min := uint16(math.MaxUint16)
	max := uint16(0)
	for x := rect.Min.X; x < rect.Max.X; x++ {
		for y := rect.Min.Y; y < rect.Max.Y; y++ {
			p := diffColor{a.At(x, y), b.At(x, y)}
			g := color.Gray16Model.Convert(p).(color.Gray16)
			if g.Y < min {
				min = g.Y
			}
			if g.Y > max {
				max = g.Y
			}
		}
	}

	// Render intensity-scaled difference.
	for x := rect.Min.X; x < rect.Max.X; x++ {
		for y := rect.Min.Y; y < rect.Max.Y; y++ {
			dst.Set(x, y, scaledColor{
				min: uint32(min), max: uint32(max),
				c: diffColor{a.At(x, y), b.At(x, y)},
			})
		}
	}

	return rect
}

type diffColor struct {
	a, b color.Color