dither.c File Reference

#include <math.h>

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Macros
#define	DMAP(v, x, y)   (modN[v]>magic[x][y] ? divN[v] + 1 : divN[v])

Functions
void	make_square ()
void	dithermap (int levels, double gamma, rgbmap, divN, modN, magic)
void	bwdithermap (int levels, double gamma, bwmap, divN, modN, magic)
void	make_square (double N, divN, modN, magic)
int	dithergb (int x, int y, int r, int g, int b, int levels, divN, modN, magic)
int	ditherbw (int x, int y, int val, divN, modN, magic)

Variables
static char	rcsid [] = "$Header: /l/spencer/src/urt/lib/RCS/dither.c,v 3.0.1.2 1992/04/30 14:07:02 spencer Exp $"
static int	magic4x4 [4][4]

Macro Definition Documentation

#define DMAP	(		v,
			x,
			y
	)		(modN[v]>magic[x][y] ? divN[v] + 1 : divN[v])

Definition at line 48 of file dither.c.

Function Documentation

void bwdithermap	(	int	levels,
		double	gamma,
		bwmap	,
		divN	,
		modN	,
		magic
	)

Definition at line 142 of file dither.c.

Referenced by init_color(), and init_monochrome_colour_map().

{
    double N;
    register int i;
    int gammamap[256];
    
    for ( i = 0; i < 256; i++ )
    gammamap[i] = (int)(0.5 + 255 * pow( i / 255.0, 1.0/gamma ));

    N = 255.0 / (levels - 1);    /* Get size of each step */

    /* 
     * Set up the color map entries.
     */
    for(i = 0; i < levels; i++)
    bwmap[i] = gammamap[(int)(0.5 + i * N)];

    make_square( N, divN, modN, magic );
}

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int ditherbw	(	int	x,
		int	y,
		int	val,
		divN	,
		modN	,
		magic
	)

Definition at line 279 of file dither.c.

{
    int col = x % 16, row = y % 16;

    return DMAP(val, col, row);
}

int dithergb	(	int	x,
		int	y,
		int	r,
		int	g,
		int	b,
		int	levels,
		divN	,
		modN	,
		magic
	)

Definition at line 247 of file dither.c.

{
    int col = x % 16, row = y % 16;

    return DMAP(r, col, row) +
    DMAP(g, col, row) * levels +
        DMAP(b, col, row) * levels*levels;
}

void dithermap	(	int	levels,
		double	gamma,
		rgbmap	,
		divN	,
		modN	,
		magic
	)

Definition at line 80 of file dither.c.

Referenced by init_8_bit_colour_map(), and init_color().

{
    double N;
    register int i;
    int levelsq, levelsc;
    int gammamap[256];
    
    for ( i = 0; i < 256; i++ )
    gammamap[i] = (int)(0.5 + 255 * pow( i / 255.0, 1.0/gamma ));

    levelsq = levels*levels;    /* squared */
    levelsc = levels*levelsq;   /* and cubed */

    N = 255.0 / (levels - 1);    /* Get size of each step */

    /* 
     * Set up the color map entries.
     */
    for(i = 0; i < levelsc; i++) {
    rgbmap[i][0] = gammamap[(int)(0.5 + (i%levels) * N)];
    rgbmap[i][1] = gammamap[(int)(0.5 + ((i/levels)%levels) * N)];
    rgbmap[i][2] = gammamap[(int)(0.5 + ((i/levelsq)%levels) * N)];
    }

    make_square( N, divN, modN, magic );
}

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void make_square

(

)

void make_square	(	double	N,
		divN	,
		modN	,
		magic
	)

Definition at line 192 of file dither.c.

Referenced by init_8_bit_color_map(), init_color(), init_dither(), and window_color_map().

{
    register int i, j, k, l;
    double magicfact;

    for ( i = 0; i < 256; i++ )
    {
    divN[i] = (int)(i / N);
    modN[i] = i - (int)(N * divN[i]);
    }
    modN[255] = 0;      /* always */

    /*
     * Expand 4x4 dither pattern to 16x16.  4x4 leaves obvious patterning,
     * and doesn't give us full intensity range (only 17 sublevels).
     * 
     * magicfact is (N - 1)/16 so that we get numbers in the matrix from 0 to
     * N - 1: mod N gives numbers in 0 to N - 1, don't ever want all
     * pixels incremented to the next level (this is reserved for the
     * pixel value with mod N == 0 at the next level).
     */
    magicfact = (N - 1) / 16.;
    for ( i = 0; i < 4; i++ )
    for ( j = 0; j < 4; j++ )
        for ( k = 0; k < 4; k++ )
        for ( l = 0; l < 4; l++ )
            magic[4*k+i][4*l+j] =
            (int)(0.5 + magic4x4[i][j] * magicfact +
                  (magic4x4[k][l] / 16.) * magicfact);
}

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Variable Documentation

int magic4x4[4][4]

static

Initial value:

=  {
{    0, 14,  3, 13},
{   11,  5,  8,  6},
{   12,  2, 15,  1},
{    7,  9,  4, 10}
}

Definition at line 40 of file dither.c.

char rcsid[] = "$Header: /l/spencer/src/urt/lib/RCS/dither.c,v 3.0.1.2 1992/04/30 14:07:02 spencer Exp $"

static

Definition at line 30 of file dither.c.