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mpv/video/out/dither.c
wm4 58a7d81dc5 gl_video: improve dithering
Use a different algorithm to generate the dithering matrix. This
looks much better than the previous ordered dither matrix with its
cross-hatch artifacts.

The matrix generation algorithm as well as its implementation was
contributed by Wessel Dankers aka Fruit. The code in dither.c is
his implementation, reformatted and with static global variables
removed by me.

The new matrix is uploaded as float texture - before this commit, it
was a normal integer fixed point matrix. This means dithering will
be disabled on systems without float textures.

The size of the dithering matrix can be configured, as the matrix is
generated at runtime. The generation of the matrix can take rather
long, and is already unacceptable with size 8. The default is at 6,
which takes about 100 ms on a Core2 Duo system with dither.c compiled
at -O2, which I consider just about acceptable.

The old ordered dithering is still available and can be selected by
putting the dither=ordered sub-option. The ordered dither matrix
generation code was moved to dither.c. This function was originally
written by Uoti Urpala.
2013-05-26 16:44:20 +02:00

240 lines
6.8 KiB
C

/******************************************************************************
dither.c - generate a dithering matrix for downsampling images
Copyright © 2013 Wessel Dankers <wsl@fruit.je>
This file is part of mpv.
mpv is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
mpv is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License along
with mpv. If not, see <http://www.gnu.org/licenses/>.
You can alternatively redistribute this file and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
******************************************************************************/
#include <stdio.h>
#include <stdint.h>
#include <stdbool.h>
#include <stdlib.h>
#include <inttypes.h>
#include <string.h>
#include <assert.h>
#include <math.h>
#include <libavutil/lfg.h>
#include "talloc.h"
#include "dither.h"
#define MAX_SIZEB 8
#define MAX_SIZE (1 << MAX_SIZEB)
#define MAX_SIZE2 (MAX_SIZE * MAX_SIZE)
typedef uint_fast32_t index_t;
#define WRAP_SIZE2(k, x) ((index_t)((index_t)(x) & ((k)->size2 - 1)))
#define XY(k, x, y) ((index_t)(((x) | ((y) << (k)->sizeb))))
struct ctx {
unsigned int sizeb, size, size2;
unsigned int gauss_radius;
unsigned int gauss_middle;
uint64_t gauss[MAX_SIZE2];
index_t randomat[MAX_SIZE2];
bool calcmat[MAX_SIZE2];
uint64_t gaussmat[MAX_SIZE2];
index_t unimat[MAX_SIZE2];
AVLFG avlfg;
};
static void makegauss(struct ctx *k, unsigned int sizeb)
{
assert(sizeb >= 1 && sizeb <= MAX_SIZEB);
memset(k, 0, sizeof(*k));
av_lfg_init(&k->avlfg, 123);
k->sizeb = sizeb;
k->size = 1 << k->sizeb;
k->size2 = k->size * k->size;
k->gauss_radius = k->size / 2 - 1;
k->gauss_middle = XY(k, k->gauss_radius, k->gauss_radius);
unsigned int gauss_size = k->gauss_radius * 2 + 1;
unsigned int gauss_size2 = gauss_size * gauss_size;
for (index_t c = 0; c < k->size2; c++)
k->gauss[c] = 0;
long double sigma = -logl(1.5 / UINT64_MAX * gauss_size2) / k->gauss_radius;
for (index_t gy = 0; gy <= k->gauss_radius; gy++) {
for (index_t gx = 0; gx <= gy; gx++) {
int cx = (int)gx - k->gauss_radius;
int cy = (int)gy - k->gauss_radius;
int sq = cx * cx + cy * cy;
long double e = expl(-sqrtl(sq) * sigma);
uint64_t v = e / gauss_size2 * UINT64_MAX;
k->gauss[XY(k, gx, gy)] =
k->gauss[XY(k, gy, gx)] =
k->gauss[XY(k, gx, gauss_size - 1 - gy)] =
k->gauss[XY(k, gy, gauss_size - 1 - gx)] =
k->gauss[XY(k, gauss_size - 1 - gx, gy)] =
k->gauss[XY(k, gauss_size - 1 - gy, gx)] =
k->gauss[XY(k, gauss_size - 1 - gx, gauss_size - 1 - gy)] =
k->gauss[XY(k, gauss_size - 1 - gy, gauss_size - 1 - gx)] = v;
}
}
uint64_t total = 0;
for (index_t c = 0; c < k->size2; c++) {
uint64_t oldtotal = total;
total += k->gauss[c];
assert(total >= oldtotal);
}
}
static void setbit(struct ctx *k, index_t c)
{
if (k->calcmat[c])
return;
k->calcmat[c] = true;
uint64_t *m = k->gaussmat;
uint64_t *me = k->gaussmat + k->size2;
uint64_t *g = k->gauss + WRAP_SIZE2(k, k->gauss_middle + k->size2 - c);
uint64_t *ge = k->gauss + k->size2;
while (g < ge)
*m++ += *g++;
g = k->gauss;
while (m < me)
*m++ += *g++;
}
static index_t getmin(struct ctx *k)
{
uint64_t min = UINT64_MAX;
index_t resnum = 0;
unsigned int size2 = k->size2;
for (index_t c = 0; c < size2; c++) {
if (k->calcmat[c])
continue;
uint64_t total = k->gaussmat[c];
if (total <= min) {
if (total != min) {
min = total;
resnum = 0;
}
k->randomat[resnum++] = c;
}
}
if (resnum == 1)
return k->randomat[0];
if (resnum == size2)
return size2 / 2;
return k->randomat[av_lfg_get(&k->avlfg) % resnum];
}
static void makeuniform(struct ctx *k)
{
unsigned int size2 = k->size2;
for (index_t c = 0; c < size2; c++) {
index_t r = getmin(k);
setbit(k, r);
k->unimat[r] = c;
}
}
// out_matrix is a reactangular tsize * tsize array, where tsize = (1 << size).
void mp_make_fruit_dither_matrix(float *out_matrix, int size)
{
struct ctx *k = talloc(NULL, struct ctx);
makegauss(k, size);
makeuniform(k);
float invscale = k->size2;
for(index_t y = 0; y < k->size; y++) {
for(index_t x = 0; x < k->size; x++)
out_matrix[x + y * k->size] = k->unimat[XY(k, x, y)] / invscale;
}
talloc_free(k);
}
void mp_make_ordered_dither_matrix(unsigned char *m, int size)
{
m[0] = 0;
for (int sz = 1; sz < size; sz *= 2) {
int offset[] = {sz*size, sz, sz * (size+1), 0};
for (int i = 0; i < 4; i++)
for (int y = 0; y < sz * size; y += size)
for (int x = 0; x < sz; x++)
m[x+y+offset[i]] = m[x+y] * 4 + (3-i) * 256/size/size;
}
}
#if 0
static int index_cmp(const void *a, const void *b)
{
index_t x = *(const index_t *)a;
index_t y = *(const index_t *)b;
return x < y ? -1 : x > y;
}
static void fsck(struct ctx *k)
{
qsort(k->unimat, k->size2, sizeof k->unimat[0], index_cmp);
for (index_t c = 0; c < k->size2; c++)
assert(k->unimat[c] == c);
}
uint16_t r[MAX_SIZE2];
static void print(struct ctx *k)
{
#if 0
puts("#include <stdint.h>");
printf("static const int mp_dither_size = %d;\n", k->size);
printf("static const int mp_dither_size2 = %d;\n", k->size2);
printf("static const uint16_t mp_dither_matrix[] = {\n");
for(index_t y = 0; y < k->size; y++) {
printf("\t");
for(index_t x = 0; x < k->size; x++)
printf("%4"PRIuFAST32", ", k->unimat[XY(k, x, y)]);
printf("\n");
}
puts("};");
#else
for(index_t y = 0; y < k->size; y++) {
for(index_t x = 0; x < k->size; x++)
r[XY(k, x, y)] = k->unimat[XY(k, x, y)];
}
#endif
}
#include "osdep/timer.h"
int main(void)
{
mp_time_init();
struct ctx *k = malloc(sizeof(struct ctx));
int64_t s = mp_time_us();
makegauss(k, 6);
makeuniform(k);
print(k);
fsck(k);
int64_t l = mp_time_us() - s;
printf("time: %f ms\n", l / 1000.0);
return 0;
}
#endif