cbG4
	cbG8
	cbGA8
	cbTC8
	cbP1
	cbP2
	cbP4
	cbP8
	cbTCA8
	cbG16
	cbGA16
	cbTC16
	cbTCA16
)

func cbPaletted(cb int) bool {
	return cbP1 <= cb && cb <= cbP8
}

func cbTrueColor(cb int) bool {
	return cb == cbTC8 || cb == cbTC16
}

// Filter type, as per the PNG spec.
const (
	ftNone    = 0
	ftSub     = 1
	ftUp      = 2
	ftAverage = 3
	ftPaeth   = 4
	nFilter   = 5
)