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authorwm4 <wm4@nowhere>2013-05-26 01:48:39 +0200
committerwm4 <wm4@nowhere>2013-05-26 16:44:20 +0200
commit58a7d81dc55835fb0f5cc6a3f14288d722f83c91 (patch)
tree2f7cce21b79b6685348aca207938512cb2917814 /video/out/dither.c
parent39225ed19676aa054aa36eb1e09b72ec712ae368 (diff)
downloadmpv-58a7d81dc55835fb0f5cc6a3f14288d722f83c91.tar.bz2
mpv-58a7d81dc55835fb0f5cc6a3f14288d722f83c91.tar.xz
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.
Diffstat (limited to 'video/out/dither.c')
-rw-r--r--video/out/dither.c239
1 files changed, 239 insertions, 0 deletions
diff --git a/video/out/dither.c b/video/out/dither.c
new file mode 100644
index 0000000000..1919010e74
--- /dev/null
+++ b/video/out/dither.c
@@ -0,0 +1,239 @@
+/******************************************************************************
+
+ 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