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/* #ident "@(#)x11:contrib/clients/xloadimage/dither.c 6.13 94/07/29 Labtam" */
/* dither.c
*
* completely reworked dithering module for xli
* uses error-diffusion dithering (floyd-steinberg) instead
* of simple 4x4 ordered-dither that was previously used
*
* the previous version of this code was written by steve losen
* (scl@virginia.edu)
*
* jim frost 07.10.89
* Steve Losen 11.17.89
* kirk johnson 06.04.90
* Graeme Gill 16/10/92 - remove tone_scale_adjust() stuff -
* gamma adjustment is better. Clean up values so
* that dithering mono images doesn't change them!
*
* Copyright 1990 Kirk L. Johnson (see the included file
* "kljcpyrght.h" for complete copyright information)
*
* Copyright 1989, 1990 Jim Frost and Steve Losen.
* See included file "copyright.h" for complete copyright information.
*/
#include "copyright.h"
#include "kljcpyrght.h"
#include "xli.h"
#define MaxGrey 65280 /* limits on the grey levels used */
#define Threshold (MaxGrey/2) /* in the dithering process */
#define MinGrey 0
static void LeftToRight(int *curr, int *next, int width);
static void RightToLeft(int *curr, int *next, int width);
/*
* simple floyd-steinberg dither with serpentine raster processing
*/
Image *dither(Image *cimage, unsigned int verbose)
{
Image *image; /* destination image */
int *grey; /* grey map for source image */
unsigned int spl; /* source pixel length in bytes */
unsigned int dll; /* destination line length in bytes */
unsigned char *src; /* source data */
unsigned char *dst; /* destination data */
int *curr; /* current line buffer */
int *next; /* next line buffer */
int *swap; /* for swapping line buffers */
Pixel color; /* pixel color */
int level; /* grey level */
unsigned int i, j; /* loop counters */
CURRFUNC("dither");
/*
* check the source image
*/
if (BITMAPP(cimage))
return(NULL);
if(GAMMA_NOT_EQUAL(cimage->gamma, 1.0))
gammacorrect(cimage, 1.0, verbose);
/*
* allocate destination image
*/
if (verbose)
{
printf(" Dithering image...");
fflush(stdout);
}
image = newBitImage(cimage->width, cimage->height);
if (cimage->title)
{
image->title = (char *)lmalloc(strlen(cimage->title) + 12);
sprintf(image->title, "%s (dithered)", cimage->title);
}
image->gamma= cimage->gamma;
/*
* if the number of entries in the colormap isn't too large, compute
* the grey level for each entry and store it in grey[]. else the
* grey levels will be computed on the fly.
*/
if (RGBP(cimage) && (cimage->depth <= 16))
{
grey = (int *)lmalloc(sizeof(int) * cimage->rgb.used);
for (i=0; i<cimage->rgb.used; i++)
grey[i]=
((int)colorIntensity(cimage->rgb.red[i],
cimage->rgb.green[i],
cimage->rgb.blue[i]));
}
else
{
grey = NULL;
}
/*
* dither setup
*/
spl = cimage->pixlen;
dll = (image->width / 8) + (image->width % 8 ? 1 : 0);
src = cimage->data;
dst = image->data;
curr = (int *)lmalloc(sizeof(int) * (cimage->width + 2));
next = (int *)lmalloc(sizeof(int) * (cimage->width + 2));
curr += 1;
next += 1;
bzero ((char *)curr, cimage->width * sizeof(*curr));
bzero ((char *)next, cimage->width * sizeof(*next));
/*
* primary dither loop
*/
for (i=0; i<cimage->height; i++)
{
/* copy the row into the current line */
for (j=0; j<cimage->width; j++)
{
color = memToVal(src, spl);
src += spl;
if (RGBP(cimage)) {
if (grey == NULL)
level = (int)colorIntensity(cimage->rgb.red[color],
cimage->rgb.green[color],
cimage->rgb.blue[color]);
else
level = (int)grey[color];
}
else {
level = (int)colorIntensity((TRUE_RED(color) << 8),
(TRUE_GREEN(color) << 8),
(TRUE_BLUE(color) << 8));
}
curr[j] += level;
}
/* dither the current line */
if (i & 0x01)
RightToLeft(curr, next, cimage->width);
else
LeftToRight(curr, next, cimage->width);
/* copy the dithered line to the destination image */
for (j=0; j<cimage->width; j++)
if (curr[j] < Threshold)
dst[j / 8] |= 1 << (7 - (j & 7));
dst += dll;
/* circulate the line buffers */
swap = curr;
curr = next;
next = swap;
bzero ((char *)next, cimage->width * sizeof(*next));
}
/*
* clean up
*/
if (grey != NULL)
lfree((byte *)grey);
lfree((byte *)(curr-1));
lfree((byte *)(next-1));
if (verbose)
printf("done\n");
return(image);
}
/*
* dither a line from left to right
*/
static void LeftToRight(int *curr, int *next, int width)
{
int idx;
int error;
int output;
if (0 < width)
{
output = (curr[0] > Threshold) ? MaxGrey : MinGrey;
error = curr[0] - output;
curr[0] = output;
next[0] += error * 5 / 16;
if (width > 1)
{
next[1] += error * 1 / 16;
curr[1] += error * 7 / 16;
}
}
for (idx=1; idx<(width-1); idx++)
{
output = (curr[idx] > Threshold) ? MaxGrey : MinGrey;
error = curr[idx] - output;
curr[idx] = output;
next[idx-1] += error * 3 / 16;
next[idx] += error * 5 / 16;
next[idx+1] += error * 1 / 16;
curr[idx+1] += error * 7 / 16;
}
idx = width -1;
if (idx > 0)
{
output = (curr[idx] > Threshold) ? MaxGrey : MinGrey;
error = curr[idx] - output;
curr[idx] = output;
next[idx-1] += error * 3 / 16;
next[idx] += error * 5 / 16;
}
}
/*
* dither a line from right to left
*/
static void RightToLeft(int *curr, int *next, int width)
{
int idx;
int error;
int output;
idx = width -1;
if (idx >= 0)
{
output = (curr[idx] > Threshold) ? MaxGrey : MinGrey;
error = curr[idx] - output;
curr[idx] = output;
next[idx] += error * 5 / 16;
if (idx > 0)
{
next[idx-1] += error * 1 / 16;
curr[idx-1] += error * 7 / 16;
}
}
for (idx=(width-2); idx>=1; idx--)
{
output = (curr[idx] > Threshold) ? MaxGrey : MinGrey;
error = curr[idx] - output;
curr[idx] = output;
next[idx+1] += error * 3 / 16;
next[idx] += error * 5 / 16;
next[idx-1] += error * 1 / 16;
curr[idx-1] += error * 7 / 16;
}
if (0 < width)
{
output = (curr[0] > Threshold) ? MaxGrey : MinGrey;
error = curr[0] - output;
curr[0] = output;
next[0] += error * 5 / 16;
}
}
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