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OrderDither.c
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C/C++ Source or Header
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1992-06-16
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2KB
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100 lines
/*
Ordered Dithering
by Stephen Hawley
from "Graphics Gems", Academic Press, 1990
*/
/* Program to generate dithering matrices.
* written by Jim Blandy, Oberlin College, jimb@occs.oberlin.edu
* Gifted to, documented and revised by Stephen Hawley,
* sdh@flash.bellcore.com
*
* Generates a dithering matrix from the command line arguments.
* The first argument, size, determines the dimensions of the
* matrix: 2^size by 2^size
* The optional range argument is the range of values to be
* dithered over. By default, it is (2^size)^2, or simply the
* total number of elements in the matrix.
* The final output is suitable for inclusion in a C program.
* A typical dithering function is something like this:
* extern int dm[], size;
*
* int
* dither(x,y, level)
* register int x,y, level;
* {
* return(level > dm[(x % size) + size * (y % size)];
* }
*/
main(argc, argv)
int argc;
char **argv;
{
register int size, range;
if (argc >= 2) size = atoi(argv[1]);
else size = 2;
if (argc == 3) range = atoi(argv[2]);
else range = (1 << size) * (1 << size);
printdither (size, range);
}
printdither (size, range)
register int size, range;
{
register int l = (1 << size), i;
/*
* print a dithering matrix.
* l is the length on a side.
*/
range = range / (l * l);
puts("int dm[] = {");
for (i=0; i < l*l; i++) {
if (i % l == 0) /* tab in 4 spaces per row */
printf(" ");
/* print the dither value for this location
* scaled to the given range
*/
printf("%4d", range * dithervalue(i / l, i % l, size));
/* commas after all but the last */
if (i + 1 < l * l)
putchar(',');
/* newline at the end of the row */
if ((i + 1) % l == 0)
putchar('\n');
}
puts("\n}; ");
}
dithervalue(x, y, size)
register int x, y, size;
{
register int d;
/*
* calculate the dither value at a particular
* (x, y) over the size of the matrix.
*/
d=0;
while (size-->0) {
/* Think of d as the density. At every iteration,
* d is shifted left one and a new bit is put in the
* low bit based on x and y. If x is odd and y is even,
* or x is even and y is odd, a bit is put in. This
* generates the checkerboard seen in dithering.
* This quantity is shifted left again and the low bit of
* y is added in.
* This whole thing interleaves a checkerboard bit pattern
* and y's bits, which is the value you want.
*/
d = (d <<1 | (x&1 ^ y&1))<<1 | y&1;
x >>= 1;
y >>= 1;
}
return(d);
}