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/*
* "$Id: dither.c 8938 2009-12-18 23:52:01Z mike $"
*
* Dithering routines for CUPS.
*
* Copyright 2007 by Apple Inc.
* Copyright 1993-2005 by Easy Software Products.
*
* These coded instructions, statements, and computer programs are the
* property of Apple Inc. and are protected by Federal copyright
* law. Distribution and use rights are outlined in the file "LICENSE.txt"
* which should have been included with this file. If this file is
* file is missing or damaged, see the license at "http://www.cups.org/".
*
* Contents:
*
* cupsDitherDelete() - Free a dithering buffer.
* cupsDitherLine() - Dither a line of pixels...
* cupsDitherNew() - Create a dithering buffer.
*/
/*
* Include necessary headers.
*/
#include "driver.h"
#include <config.h>
/*
* 'cupsDitherDelete()' - Free a dithering buffer.
*
* Returns 0 on success, -1 on failure.
*/
void
cupsDitherDelete(cups_dither_t *d) /* I - Dithering buffer */
{
if (d != NULL)
free(d);
}
/*
* 'cupsDitherLine()' - Dither a line of pixels...
*/
void
cupsDitherLine(cups_dither_t *d, /* I - Dither data */
const cups_lut_t *lut, /* I - Lookup table */
const short *data, /* I - Separation data */
int num_channels,
/* I - Number of components */
unsigned char *p) /* O - Pixels */
{
register int x, /* Horizontal position in line... */
pixel, /* Current adjusted pixel... */
e, /* Current error */
e0,e1,e2; /* Error values */
register int errval0, /* First half of error value */
errval1, /* Second half of error value */
errbase, /* Base multiplier */
errbase0, /* Base multiplier for large values */
errbase1, /* Base multiplier for small values */
errrange; /* Range of random multiplier */
register int *p0, /* Error buffer pointers... */
*p1;
static char logtable[16384]; /* Error magnitude for randomness */
static char loginit = 0; /* Has the table been initialized? */
if (!loginit)
{
/*
* Initialize a logarithmic table for the magnitude of randomness
* that is introduced.
*/
loginit = 1;
logtable[0] = 0;
for (x = 1; x < 2049; x ++)
logtable[x] = (int)(log(x / 16.0) / log(2.0) + 1.0);
for (; x < 16384; x ++)
logtable[x] = logtable[2049];
}
if (d->row == 0)
{
/*
* Dither from left to right:
*
* e0 == p0[0]
* e1 e2 == p1[-1] p1[0]
*/
p0 = d->errors + 2;
p1 = d->errors + 2 + d->width + 4;
e0 = p0[0];
e1 = 0;
e2 = 0;
/*
* Error diffuse each output pixel...
*/
for (x = d->width;
x > 0;
x --, p0 ++, p1 ++, p ++, data += num_channels)
{
/*
* Skip blank pixels...
*/
if (*data == 0)
{
*p = 0;
e0 = p0[1];
p1[-1] = e1;
e1 = e2;
e2 = 0;
continue;
}
/*
* Compute the net pixel brightness and brightness error. Set a dot
* if necessary...
*/
pixel = lut[*data].intensity + e0 / 128;
if (pixel > CUPS_MAX_LUT)
pixel = CUPS_MAX_LUT;
else if (pixel < 0)
pixel = 0;
*p = lut[pixel].pixel;
e = lut[pixel].error;
/*
* Set the randomness factor...
*/
if (e > 0)
errrange = logtable[e];
else
errrange = logtable[-e];
errbase = 8 - errrange;
errrange = errrange * 2 + 1;
/*
* Randomize the error value.
*/
if (errrange > 1)
{
errbase0 = errbase + (CUPS_RAND() % errrange);
errbase1 = errbase + (CUPS_RAND() % errrange);
}
else
errbase0 = errbase1 = errbase;
/*
* X 7/16 = X e0
* 3/16 5/16 1/16 = e1 e2
*/
errval0 = errbase0 * e;
errval1 = (16 - errbase0) * e;
e0 = p0[1] + 7 * errval0;
e1 = e2 + 5 * errval1;
errval0 = errbase1 * e;
errval1 = (16 - errbase1) * e;
e2 = errval0;
p1[-1] = e1 + 3 * errval1;
}
}
else
{
/*
* Dither from right to left:
*
* e0 == p0[0]
* e2 e1 == p1[0] p1[1]
*/
p0 = d->errors + d->width + 1 + d->width + 4;
p1 = d->errors + d->width + 1;
p += d->width - 1;
data += num_channels * (d->width - 1);
e0 = p0[0];
e1 = 0;
e2 = 0;
/*
* Error diffuse each output pixel...
*/
for (x = d->width;
x > 0;
x --, p0 --, p1 --, p --, data -= num_channels)
{
/*
* Skip blank pixels...
*/
if (*data == 0)
{
*p = 0;
e0 = p0[-1];
p1[1] = e1;
e1 = e2;
e2 = 0;
continue;
}
/*
* Compute the net pixel brightness and brightness error. Set a dot
* if necessary...
*/
pixel = lut[*data].intensity + e0 / 128;
if (pixel > CUPS_MAX_LUT)
pixel = CUPS_MAX_LUT;
else if (pixel < 0)
pixel = 0;
*p = lut[pixel].pixel;
e = lut[pixel].error;
/*
* Set the randomness factor...
*/
if (e > 0)
errrange = logtable[e];
else
errrange = logtable[-e];
errbase = 8 - errrange;
errrange = errrange * 2 + 1;
/*
* Randomize the error value.
*/
if (errrange > 1)
{
errbase0 = errbase + (CUPS_RAND() % errrange);
errbase1 = errbase + (CUPS_RAND() % errrange);
}
else
errbase0 = errbase1 = errbase;
/*
* X 7/16 = X e0
* 3/16 5/16 1/16 = e1 e2
*/
errval0 = errbase0 * e;
errval1 = (16 - errbase0) * e;
e0 = p0[-1] + 7 * errval0;
e1 = e2 + 5 * errval1;
errval0 = errbase1 * e;
errval1 = (16 - errbase1) * e;
e2 = errval0;
p1[1] = e1 + 3 * errval1;
}
}
/*
* Update to the next row...
*/
d->row = 1 - d->row;
}
/*
* 'cupsDitherNew()' - Create an error-diffusion dithering buffer.
*/
cups_dither_t * /* O - New state array */
cupsDitherNew(int width) /* I - Width of output in pixels */
{
cups_dither_t *d; /* New dithering buffer */
if ((d = (cups_dither_t *)calloc(1, sizeof(cups_dither_t) +
2 * (width + 4) *
sizeof(int))) == NULL)
return (NULL);
d->width = width;
return (d);
}
/*
* End of "$Id: dither.c 8938 2009-12-18 23:52:01Z mike $".
*/
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