_, e.err = e.w.Write(e.header[:8])
	if e.err != nil {
		return
	}
	_, e.err = e.w.Write(b)
	if e.err != nil {
		return
	}
	_, e.err = e.w.Write(e.footer[:4])
}

func (e *encoder) writeIHDR() {
	b := e.m.Bounds()
	binary.BigEndian.PutUint32(e.tmp[0:4], uint32(b.Dx()))
	binary.BigEndian.PutUint32(e.tmp[4:8], uint32(b.Dy()))
	// Set bit depth and color type.
	switch e.cb {
	case cbG8: