t.Fatalf("bounds differ: %v and %v", m0.Bounds(), m1.Bounds())
	}
	if averageDelta(m0, m1) != 0 {
		t.Fatalf("images differ")
	}
}

// palettesEqual reports whether two color.Palette values are equal, ignoring
// any trailing opaque-black palette entries.
func palettesEqual(p, q color.Palette) bool {
	n := len(p)
	if n > len(q) {
		n = len(q)
	}
	for i := 0; i < n; i++ {
		if p[i] != q[i] {
			return false