: intensity cog >r 4 ndrop r> ;	# average intensity

# contrast:  (1-x) image + (x) average

: agc >r dup intensity r> swap / * ;

: contrast 
	>r unpack r>
	over intensity over + >r
	-1.0 * over swap * + r> +
	3 image:join ;
		
# unpack image into 3 equal size single plane images
: plane:unpack-3
	unpack type		# get type symbol for first plane
	swap over convert >r
	swap over convert >r
	convert r> r> ;

# YUV conversion: this needs checking
# probably a lot more convenient to build libtile programs for these

# Y = 0.299R + 0.587G + 0.114B
# U'= (B-Y)*0.565
# V'= (R-Y)*0.713


0.299 constant coef-r
0.587 constant coef-g
0.114 constant coef-b
0.565 constant coef-u
0.713 constant coef-v

# color space conversion: input needs to have a list of 3 channels
# FIXME: this no work

: plane:rgb->Y 
	coef-b *
	swap coef-g *+
	swap coef-r *+ ;
	
: plane:rgb->P411
	3 pack dup unpack
	plane:rgb->Y >r		# get luma
	unpack swap drop	# ( b r )
	r  - .565 * swap
	r  - .713 * swap 	# ( Cb Cr )
	r> ; 			# ( Cb Cr Y )
	

: rgb->P411
	plane:unpack-3 
	plane:rgb->P411
	>r image:halve swap image:halve swap r>
	3 image:join ;