deflng a-z

img1 = _loadimage("img/zmago.jpg", 32)

w = _width(img1)
h = _height(img1)

img2 = _newimage(w, h, 32)
img3 = _newimage(w, h, 32)
img4 = _newimage(w, h, 32)

img5 = _newimage(w, h, 32)
img6 = _newimage(w, h, 32)
img7 = _newimage(w, h, 32)

img8 = _newimage(w, h, 32)
img9 = _newimage(w, h, 32)
img10 = _newimage(w, h, 32)

screen _newimage(w*3, h*3, 32)

redim h(2, 1) as single
h(0,0)=0:h(1,0)=-1:h(2,0)=7/16
h(0,1)=3/16:h(1,1)=5/16:h(2,1)=1/16

dither_bw img1, img2, 0.1, h()
dither img1, img3, 2, h()
dither img1, img4, 4, h()

redim h(4, 2) as single
h(0,0)=0:h(1,0)=0:h(2,0)=-1:h(3,0)=7/48:h(4,0)=5/48
h(0,1)=3/48:h(1,1)=5/48:h(2,1)=7/48:h(3,1)=5/48:h(4,1)=3/48
h(0,2)=1/48:h(1,2)=3/48:h(2,2)=5/48:h(3,2)=3/48:h(4,2)=1/48

dither_bw img1, img5, 0.1, h()
dither img1, img6, 2, h()
dither img1, img7, 4, h()

redim h(3, 2) as single
h(0,0)=0:h(1,0)=-1:h(2,0)=1/8:h(3,0)=1/8
h(0,1)=1/8:h(1,1)=1/8:h(2,1)=1/8:h(3,1)=0
h(0,2)=0:h(1,2)=1/8:h(2,2)=0:h(3,2)=0

dither_bw img1, img8, 0.1, h()
dither img1, img9, 2, h()
dither img1, img10, 4, h()

_dest 0
_putimage (0, 0), img2
_putimage (w, 0), img3
_putimage (2*w, 0), img4
_printstring (0,0),"Floyd-Steinberg"

_putimage (0, h), img5
_putimage (w, h), img6
_putimage (2*w, h), img7
_printstring (0,h),"Jarvis, Judice, and Ninke"

_putimage (0, 2*h), img8
_putimage (w, 2*h), img9
_putimage (2*w, 2*h), img10
_printstring (0,2*h),"Atkinson"


do
loop until _keyhit=27
system

'colour dither
'source image, destination image, number of colours per channel, diffusion matrix
sub dither(img1, img2, num, h() as single)
	w = _width(img1)
	h = _height(img1)

	_dest img2
	_source img2

	_putimage , img1

	for y=0 to h-1
	for x=0 to w-1

		z = point(x, y)

		r = (_red(z)*num\255)*255\num
		g = (_green(z)*num\255)*255\num
		b = (_blue(z)*num\255)*255\num

		pset (x, y), _rgb(r, g, b)

		qr = _red(z) - r
		qg = _green(z) - g
		qb = _blue(z) - b

		conv_ed img2, x, y, h(), qr, qg, qb
	next
	next
end sub

'black and white dither
'source image, destination image, bw threshold percent, diffusion matrix
sub dither_bw(img1, img2, t as double, h() as single)
	w = _width(img1)
	h = _height(img1)

	_dest img2
	_source img2

	_putimage , img1

	for y=0 to h-1
	for x=0 to w-1

		z = point(x, y)

		c = -((_red(z)+_green(z)+_blue(z))/3 > 255*t)*255

		pset (x, y), _rgb(c, c, c)

		qr = _red(z) - c
		qg = _green(z) - c
		qb = _blue(z) - c

		conv_ed img2, x, y, h(), qr, qg, qb
	next
	next
end sub

sub conv_ed(img, x0, y0, h() as single, qr, qg, qb)
	for y=0 to ubound(h,2)
	for x=0 to ubound(h,1)
		if h(x,y)=-1 then 
			xx = x
			yy = y
		end if
	next
	next

	_source img
	_dest img

	for y=0 to ubound(h,2)
	for x=0 to ubound(h,1)
		if h(x,y)<>-1 and h(x,y)<>0 then
			r = _red(point(x0-xx+x, y0-yy+y)) + qr*h(x,y)
			g = _green(point(x0-xx+x, y0-yy+y)) + qg*h(x,y)
			b = _blue(point(x0-xx+x, y0-yy+y)) + qb*h(x,y)
			
			pset (x0-xx+x, y0-yy+y), _rgb(r, g, b)
		end if
	next
	next
end sub