gstreamer/gst/dvbsubenc/libimagequant/nearest.c

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#include "libimagequant.h"
#include "pam.h"
#include "nearest.h"
#include "mempool.h"
#include <stdlib.h>
struct sorttmp
{
float radius;
unsigned int index;
};
struct head
{
// colors less than radius away from vantage_point color will have best match in candidates
f_pixel vantage_point;
float radius;
unsigned int num_candidates;
f_pixel *candidates_color;
unsigned short *candidates_index;
};
struct nearest_map
{
const colormap *map;
float nearest_other_color_dist[256];
mempool mempool;
struct head heads[];
};
static float
distance_from_nearest_other_color (const colormap * map, const unsigned int i)
{
float second_best = MAX_DIFF;
for (unsigned int j = 0; j < map->colors; j++) {
float diff;
if (i == j)
continue;
diff = colordifference (map->palette[i].acolor, map->palette[j].acolor);
if (diff <= second_best) {
second_best = diff;
}
}
return second_best;
}
static int
compareradius (const void *ap, const void *bp)
{
float a = ((const struct sorttmp *) ap)->radius;
float b = ((const struct sorttmp *) bp)->radius;
return a > b ? 1 : (a < b ? -1 : 0);
}
static struct head
build_head (f_pixel px, const colormap * map, unsigned int num_candidates,
mempool * m, float error_margin, bool skip_index[], unsigned int *skipped)
{
struct sorttmp *colors = g_alloca (sizeof (struct sorttmp) * map->colors);
unsigned int colorsused, i;
struct head h;
colorsused = 0;
for (i = 0; i < map->colors; i++) {
if (skip_index[i])
continue; // colors in skip_index have been eliminated already in previous heads
colors[colorsused].index = i;
colors[colorsused].radius = colordifference (px, map->palette[i].acolor);
colorsused++;
}
qsort (colors, colorsused, sizeof (colors[0]), compareradius);
assert (colorsused < 2 || colors[0].radius <= colors[1].radius); // closest first
num_candidates = MIN (colorsused, num_candidates);
h.candidates_color =
mempool_alloc (m, num_candidates * sizeof (h.candidates_color[0]), 0);
h.candidates_index =
mempool_alloc (m, num_candidates * sizeof (h.candidates_index[0]), 0);
h.vantage_point = px;
h.num_candidates = num_candidates;
for (i = 0; i < num_candidates; i++) {
h.candidates_color[i] = map->palette[colors[i].index].acolor;
h.candidates_index[i] = colors[i].index;
}
// if all colors within this radius are included in candidates, then there cannot be any other better match
// farther away from the vantage point than half of the radius. Due to alpha channel must assume pessimistic radius.
h.radius = min_colordifference (px, h.candidates_color[num_candidates - 1]) / 4.0f; // /4 = half of radius, but radius is squared
for (i = 0; i < num_candidates; i++) {
// divide again as that's matching certain subset within radius-limited subset
// - 1/256 is a tolerance for miscalculation (seems like colordifference isn't exact)
if (colors[i].radius < h.radius / 4.f - error_margin) {
skip_index[colors[i].index] = true;
(*skipped)++;
}
}
return h;
}
static colormap *
get_subset_palette (const colormap * map)
{
unsigned int subset_size, i;
colormap *subset_palette;
if (map->subset_palette) {
return map->subset_palette;
}
subset_size = (map->colors + 3) / 4;
subset_palette = pam_colormap (subset_size, map->malloc, map->free);
for (i = 0; i < subset_size; i++) {
subset_palette->palette[i] = map->palette[i];
}
return subset_palette;
}
LIQ_PRIVATE struct nearest_map *
nearest_init (const colormap * map, bool fast)
{
colormap *subset_palette = get_subset_palette (map);
const unsigned int num_vantage_points =
map->colors > 16 ? MIN (map->colors / (fast ? 4 : 3),
subset_palette->colors) : 0;
const unsigned long heads_size = sizeof (struct head) * (num_vantage_points + 1); // +1 is fallback head
const unsigned long mempool_size =
(sizeof (f_pixel) +
sizeof (unsigned int)) * subset_palette->colors * map->colors / 5 +
(1 << 14);
mempool m = NULL;
struct nearest_map *centroids = mempool_create (&m,
sizeof (*centroids) + heads_size /* heads array is appended to it */ ,
mempool_size, map->malloc, map->free);
unsigned int skipped;
const float error_margin = fast ? 0 : 8.f / 256.f / 256.f;
unsigned int h, i, j;
bool *skip_index;
centroids->mempool = m;
for (i = 0; i < map->colors; i++) {
const float dist = distance_from_nearest_other_color (map, i);
centroids->nearest_other_color_dist[i] = dist / 4.f; // half of squared distance
}
centroids->map = map;
skipped = 0;
assert (map->colors > 0);
skip_index = g_alloca (sizeof (bool) * map->colors);
for (j = 0; j < map->colors; j++)
skip_index[j] = false;
// floats and colordifference calculations are not perfect
for (h = 0; h < num_vantage_points; h++) {
unsigned int num_candiadtes =
1 + (map->colors - skipped) / ((1 + num_vantage_points - h) / 2);
centroids->heads[h] =
build_head (subset_palette->palette[h].acolor, map, num_candiadtes,
&centroids->mempool, error_margin, skip_index, &skipped);
if (centroids->heads[h].num_candidates == 0) {
break;
}
}
// assumption that there is no better color within radius of vantage point color
// holds true only for colors within convex hull formed by palette colors.
// The fallback must contain all colors, since there are too many edge cases to cover.
if (!fast)
for (j = 0; j < map->colors; j++) {
skip_index[j] = false;
}
centroids->heads[h] = build_head ((f_pixel) {
0, 0, 0, 0}
, map, map->colors, &centroids->mempool, error_margin,
skip_index, &skipped);
centroids->heads[h].radius = MAX_DIFF;
// get_subset_palette could have created a copy
if (subset_palette != map->subset_palette) {
pam_freecolormap (subset_palette);
}
return centroids;
}
LIQ_PRIVATE unsigned int
nearest_search (const struct nearest_map *centroids, const f_pixel px,
int likely_colormap_index, const float min_opaque_val, float *diff)
{
const bool iebug = px.a > min_opaque_val;
const struct head *const heads = centroids->heads;
float guess_diff;
unsigned int i;
assert (likely_colormap_index < centroids->map->colors);
guess_diff =
colordifference (centroids->map->palette[likely_colormap_index].acolor,
px);
if (guess_diff < centroids->nearest_other_color_dist[likely_colormap_index]) {
if (diff)
*diff = guess_diff;
return likely_colormap_index;
}
for (i = 0; /* last head will always be selected */ ; i++) {
float vantage_point_dist = colordifference (px, heads[i].vantage_point);
if (vantage_point_dist <= heads[i].radius) {
unsigned int ind = 0;
float dist;
assert (heads[i].num_candidates);
dist = colordifference (px, heads[i].candidates_color[0]);
/* penalty for making holes in IE */
if (iebug && heads[i].candidates_color[0].a < 1) {
dist += 1.f / 1024.f;
}
for (unsigned int j = 1; j < heads[i].num_candidates; j++) {
float newdist = colordifference (px, heads[i].candidates_color[j]);
/* penalty for making holes in IE */
if (iebug && heads[i].candidates_color[j].a < 1) {
newdist += 1.f / 1024.f;
}
if (newdist < dist) {
dist = newdist;
ind = j;
}
}
if (diff)
*diff = dist;
return heads[i].candidates_index[ind];
}
}
}
LIQ_PRIVATE void
nearest_free (struct nearest_map *centroids)
{
mempool_destroy (centroids->mempool);
}