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/* HAM8 encoding, based on the jpegAGA HAM8 encoding
* Originally by Gnther Rhrich
* Converted to C by Chris Lawrence <lawrencc@debian.org>
*
* Copyright 1996-99 by Chris Lawrence
*
* This file is subject to the terms and conditions of the GNU General Public
* License. See the file COPYING in the main directory of the Linux
* distribution for more details.
*/
#ifndef VIDEO_HAM
int encodeham8; /* Declare something so things don't act too weird */
#else
#undef HISTOGRAM_WEIRDNESS
#include <sys/types.h>
#include <stdlib.h>
#include <string.h>
#include <ppm.h>
extern void Die(const char *fmt,...) __attribute__((noreturn));
extern u_char ColorTable[64 * 3];
extern u_char *ColorCache;
extern int depth;
static u_int16_t compute_error(u_char orig[3], u_char chosen[3]);
void EncodeHAM(pixel * pixrow, pixval maxval, u_char * yham, u_int16_t xsize,
int do_histogram);
static inline u_int16_t square(u_int16_t x)
{
return x*x;
}
static u_int16_t compute_error(u_char orig[3], u_char chosen[3])
{
u_int16_t ret, x;
x = orig[0] - chosen[0];
ret = square(x);
x = orig[1] - chosen[1];
ret += square(x);
x = orig[2] - chosen[2];
ret += square(x);
return ret;
}
#define HAM_ENTRIES (1 << (depth-2)) /* 2^(depth-2) */
#define HAM_COLORS (HAM_ENTRIES - 1) /* 2^(depth-2) - 1 */
static inline char map_ham(char ham, char value)
{
if( depth == 8 ) {
return (value << 2) | ham;
} else {
return (ham << (depth-2)) | value;
}
}
void EncodeHAM(pixel *pixrow, pixval maxval, u_char *pos, u_int16_t xsize,
int do_histogram)
{
u_char orig_cols[3], left[3], cache, *finham;
u_char best_color = 0, colcount = 0, ham_offset, tmp, tmp2, change_val;
u_int32_t CacheOffset, offset;
u_int16_t err, min_error;
int i;
/* Force choosing a color for the first pixel */
left[0] = left[1] = left[2] = 255;
finham = (pos + xsize);
while( pos < finham ) {
pixel p;
PPM_DEPTH(p, (*pixrow), maxval, HAM_COLORS);
pixrow++;
orig_cols[0] = PPM_GETB(p);
orig_cols[1] = PPM_GETR(p);
orig_cols[2] = PPM_GETG(p);
if( left[0] == orig_cols[0] &&
left[1] == orig_cols[1] &&
left[2] == orig_cols[2] ) {
/* This pixel is identical to the previous one */
ham_offset = colcount;
colcount = (colcount + 1) % 3;
left[ham_offset] = orig_cols[ham_offset];
*(pos++) = map_ham(ham_offset+1, orig_cols[ham_offset]);
} else {
offset = (orig_cols[1] << 12) | (orig_cols[2] << 6) | orig_cols[0];
cache = ColorCache[offset];
if (!cache) { /* No cached color: find index of best color in palette */
CacheOffset = offset;
best_color = offset = 0;
min_error = 3*square(HAM_ENTRIES);
do {
err = compute_error(orig_cols, &ColorTable[offset]);
if (err < min_error) {
min_error = err;
best_color = offset;
}
offset += 3;
} while (err > 0 && offset < (3 * HAM_ENTRIES));
ColorCache[CacheOffset] = best_color;
} else { /* There is a cached color */
#ifdef HISTOGRAM_WEIRDNESS
if (!do_histogram) {
*(pos++) = map_ham(0, cache/3);
left[0] = ColorTable[cache];
left[1] = ColorTable[cache+1];
left[2] = ColorTable[cache+2];
continue;
}
#endif
best_color = cache;
min_error = compute_error(orig_cols, &ColorTable[best_color]);
}
tmp2 = abs(orig_cols[0] - left[0]);
change_val = orig_cols[0];
ham_offset = 0;
for(i=1; i<3; i++) {
tmp = abs(orig_cols[i] - left[i]);
if( tmp > tmp2 ) {
change_val = orig_cols[i];
ham_offset = i;
tmp2 = tmp;
}
}
left[ham_offset] = change_val;
err = compute_error(orig_cols, left);
if (min_error >= err) {
/* Hold-and-Modify pixel to the left */
*(pos++) = map_ham(ham_offset+1, change_val);
} else { /* Use palette entry */
*(pos++) = map_ham(0, best_color/3);
left[0] = ColorTable[best_color];
left[1] = ColorTable[best_color+1];
left[2] = ColorTable[best_color+2];
}
}
}
return;
}
#endif
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