// ignorable) for the ctTrueColor and ctTrueColorAlpha color types (section 4.1.2).
	default:
		return FormatError("PLTE, color type mismatch")
	}
	return d.verifyChecksum()
}

func (d *decoder) parsetRNS(length uint32) error {
	switch d.cb {
	case cbG1, cbG2, cbG4, cbG8, cbG16:
		if length != 2 {
			return FormatError("bad tRNS length")
		}
		n, err := io.ReadFull(d.r, d.tmp[:length])
		if err != nil {