)

func readImg(filename string) (image.Image, error) {
	f, err := os.Open(filename)
	if err != nil {
		return nil, err
	}
	defer f.Close()
	m, _, err := image.Decode(f)
	return m, err
}

func readGIF(filename string) (*GIF, error) {
	f, err := os.Open(filename)
	if err != nil {
		return nil, err
	}
	defer f.Close()
	return DecodeAll(f)
}

func delta(u0, u1 uint32) int64 {
	d := int64(u0) - int64(u1)