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← Older revision		Revision as of 15:57, 20 September 2015
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		+	* http://forum.doom9.org/showthread.php?p=1509153#post1509153
		+	* http://www.virtualdub.org/blog/pivot/entry.php?id=151
		+	* https://engineering.purdue.edu/~bouman/ece637/notes/pdf/Halftoning.pdf (page 11)
		+
		+	It is ordered input dithering with a 02/31 recursive Bayer pattern (contrast normal 13/42 pattern) modified for equal sums in both rows and columns. Avery
		+
		+	Lee described the recursive generation in his blog a while ago on Dithering. I modified the resultant pattern for equal summing to eliminate an obvious
		+
		+	pattern visible in 16x16 cells.
		+
		+	The dithering is added as an extra lower 8 bits (4bits for chroma) on the input pixels, making 16bit data. This is then used as an index into a 65K LUT to
		+
		+	get the output 8 bit pixel. The dither pattern effectively replaces the 0.5 rounding term in generating the LUT.
		+
		+	without dithering:
		+
		+	i = 0..255
		+	mapR[i] = int(min(max(i * r/255.0, 0.0), 1.0) * 255.0 + 0.5);
		+	example: r=2, i=16 => mapR[16] = int(32/255.0 * 255.0 + 0.5) = 32
		+
		+	for (int y=0; y<vi.height; ++y) {
		+	for (int x=0; x<vi.width; ++x) {
		+	p[x] = map[p[x]];
		+	}
		+	p += pitch;
		+	}
		+
		+	with dithering:
		+
		+	i = 0..256*256-1
		+	mapR[i] = int(min(max(i * r - 127.5)/(255.0256), 0.0), 1.0) 255.0 + 0.5);
		+	example: r=2, i=16256 => mapR[16256] = int((32256 - 127.5)/(255.0256) * 255.0 + 0.5) = 32
		+	bias = -127.5 ??
		+
		+	for (int y=0; y<vi.height; ++y) {
		+	const int _y = (y << 4) & 0xf0;
		+	for (int x=0; x<vi.width; ++x) {
		+	p[x] = map[ p[x]<<8 \| ditherMap[(x&0x0f)\|_y] ];
		+	}
		+	p += pitch;
		+	}
		+
		+	// 16x16 dither table:
		+	_y = (y << 4) & 0xf0 = ...
		+	ditherMap[(x&0x0f)\|_y] = ...
		+
		+	y=15+3 => _y = (y << 4) & 0xf0 = 18/2^4 & (f16 + 01) = 18/16 & 15*16 = 1 & 1111 0000 = 0
		+	y=1516 => _y = (y << 4) & 0xf0 = 1516/2^4 & (f16 + 01) = 15 & 15*16 = 1111 & 1111 0000 = 0
		+	ditherMap[(x&0x0f)\|_y] = ditherMap[(x & 1111) \| 0] = ditherMap[x & 1111]
		+	y=1616 => _y = (y << 4) & 0xf0 = 1616/2^4 & (f16 + 01) = 16 & 15*16 = 1 0000 & 1111 0000 = 1
		+	ditherMap[(x&0x0f)\|_y] = ditherMap[(x & 1111) \| 1]
		+	* so each 256 pixels, the offset in ditherMap is shifted by one.
		+
		+	// 4x4 dither table:
		+	const int _y = (y << 2) & 0xC;
		+	ditherMap4[(x&0x3)\|_y];
		+
		+	http://web.archive.org/web/20130512190753/http://white.stanford.edu/~brian/psy221/reader/Bayer.1973.pdf

	[[Category:Glossary]]		[[Category:Glossary]]

← Older revision		Revision as of 22:00, 23 June 2014
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		+	[[Category:Glossary]]

Ordered dithering - Revision history

Admin at 15:57, 20 September 2015

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Admin: Created page with "todo"