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avfilter/palettegen: base box split decision on a perceptual model

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Similar to the change in paletteuse, we rely on a perceptual model to
decide how and where to split the box.
This commit is contained in:
Clément Bœsch
2022-12-27 15:33:15 +01:00
parent 724f52b906
commit 9026d92c13
4 changed files with 29 additions and 25 deletions
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2
libavfilter/Makefile
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@@ -403,7 +403,7 @@ OBJS-$(CONFIG_OVERLAY_VULKAN_FILTER) += vf_overlay_vulkan.o vulkan.o vul
OBJS-$(CONFIG_OWDENOISE_FILTER) += vf_owdenoise.o
OBJS-$(CONFIG_PAD_FILTER) += vf_pad.o
OBJS-$(CONFIG_PAD_OPENCL_FILTER) += vf_pad_opencl.o opencl.o opencl/pad.o
OBJS-$(CONFIG_PALETTEGEN_FILTER) += vf_palettegen.o
OBJS-$(CONFIG_PALETTEGEN_FILTER) += vf_palettegen.o palette.o
OBJS-$(CONFIG_PALETTEUSE_FILTER) += vf_paletteuse.o framesync.o palette.o
OBJS-$(CONFIG_PERMS_FILTER) += f_perms.o
OBJS-$(CONFIG_PERSPECTIVE_FILTER) += vf_perspective.o

48
libavfilter/vf_palettegen.c
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@@ -30,16 +30,19 @@
#include "libavutil/intreadwrite.h"
#include "avfilter.h"
#include "internal.h"
#include "palette.h"
/* Reference a color and how much it's used */
struct color_ref {
uint32_t color;
struct Lab lab;
int64_t count;
};
/* Store a range of colors */
struct range_box {
uint32_t color; // average color
struct Lab avg; // average color in perceptual OkLab space
int major_axis; // best axis candidate for cutting the box
int64_t weight; // sum of all the weights of the colors
int64_t cut_score; // how likely the box is to be cut down (higher implying more likely)
@@ -115,15 +118,14 @@ static int cmp_##name(const void *pa, const void *pb) \
{ \
const struct color_ref * const *a = pa; \
const struct color_ref * const *b = pb; \
return (int)((*a)->color >> (8 * (2 - (pos))) & 0xff) \
- (int)((*b)->color >> (8 * (2 - (pos))) & 0xff); \
return FFDIFFSIGN((*a)->lab.name, (*b)->lab.name); \
}
DECLARE_CMP_FUNC(r, 0)
DECLARE_CMP_FUNC(g, 1)
DECLARE_CMP_FUNC(L, 0)
DECLARE_CMP_FUNC(a, 1)
DECLARE_CMP_FUNC(b, 2)
static const cmp_func cmp_funcs[] = {cmp_r, cmp_g, cmp_b};
static const cmp_func cmp_funcs[] = {cmp_L, cmp_a, cmp_b};
/**
* Simple color comparison for sorting the final palette
@@ -137,40 +139,38 @@ static int cmp_color(const void *a, const void *b)
static void compute_box_stats(PaletteGenContext *s, struct range_box *box)
{
int avg[3];
int64_t er2[3] = {0};
/* Compute average color */
int64_t sr = 0, sg = 0, sb = 0;
int64_t sL = 0, sa = 0, sb = 0;
box->weight = 0;
for (int i = box->start; i < box->start + box->len; i++) {
const struct color_ref *ref = s->refs[i];
sr += (ref->color >> 16 & 0xff) * ref->count;
sg += (ref->color >> 8 & 0xff) * ref->count;
sb += (ref->color & 0xff) * ref->count;
sL += ref->lab.L * ref->count;
sa += ref->lab.a * ref->count;
sb += ref->lab.b * ref->count;
box->weight += ref->count;
}
avg[0] = sr / box->weight;
avg[1] = sg / box->weight;
avg[2] = sb / box->weight;
box->color = 0xffU<<24 | avg[0]<<16 | avg[1]<<8 | avg[2];
box->avg.L = sL / box->weight;
box->avg.a = sa / box->weight;
box->avg.b = sb / box->weight;
/* Compute squared error of each color channel */
for (int i = box->start; i < box->start + box->len; i++) {
const struct color_ref *ref = s->refs[i];
const int64_t dr = (int)(ref->color >> 16 & 0xff) - avg[0];
const int64_t dg = (int)(ref->color >> 8 & 0xff) - avg[1];
const int64_t db = (int)(ref->color & 0xff) - avg[2];
er2[0] += dr * dr * ref->count;
er2[1] += dg * dg * ref->count;
const int64_t dL = ref->lab.L - box->avg.L;
const int64_t da = ref->lab.a - box->avg.a;
const int64_t db = ref->lab.b - box->avg.b;
er2[0] += dL * dL * ref->count;
er2[1] += da * da * ref->count;
er2[2] += db * db * ref->count;
}
/* Define the best axis candidate for cutting the box */
box->major_axis = 1; // pick green by default (the color the eye is the most sensitive to)
box->major_axis = 0;
if (er2[2] >= er2[0] && er2[2] >= er2[1]) box->major_axis = 2;
if (er2[1] >= er2[0] && er2[1] >= er2[2]) box->major_axis = 1;
if (er2[0] >= er2[1] && er2[0] >= er2[2]) box->major_axis = 0;
if (er2[1] >= er2[0] && er2[1] >= er2[2]) box->major_axis = 1; // prefer green again
/* The box that has the axis with the biggest error amongst all boxes will but cut down */
box->cut_score = FFMAX3(er2[0], er2[1], er2[2]);
@@ -318,7 +318,7 @@ static AVFrame *get_palette_frame(AVFilterContext *ctx)
ff_dlog(ctx, "box #%02X [%6d..%-6d] (%6d) w:%-6"PRIu64" sort by %c (already sorted:%c) ",
box_id, box->start, box->start + box->len - 1, box->len, box->weight,
"rgb"[box->major_axis], box->sorted_by == box->major_axis ? 'y':'n');
"Lab"[box->major_axis], box->sorted_by == box->major_axis ? 'y':'n');
/* sort the range by its major axis if it's not already sorted */
if (box->sorted_by != box->major_axis) {
@@ -348,6 +348,9 @@ static AVFrame *get_palette_frame(AVFilterContext *ctx)
av_log(ctx, AV_LOG_INFO, "%d%s colors generated out of %d colors; ratio=%f\n",
s->nb_boxes, s->reserve_transparent ? "(+1)" : "", s->nb_refs, ratio);
for (int i = 0; i < s->nb_boxes; i++)
s->boxes[i].color = 0xffU<<24 | ff_oklab_int_to_srgb_u8(s->boxes[i].avg);
qsort(s->boxes, s->nb_boxes, sizeof(*s->boxes), cmp_color);
write_palette(ctx, out);
@@ -392,6 +395,7 @@ static int color_inc(struct hist_node *hist, uint32_t color)
if (!e)
return AVERROR(ENOMEM);
e->color = color;
e->lab = ff_srgb_u8_to_oklab_int(color);
e->count = 1;
return 1;
}

2
tests/ref/fate/filter-palettegen-1
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@@ -3,4 +3,4 @@
#codec_id 0: rawvideo
#dimensions 0: 16x16
#sar 0: 1/1
0, 0, 0, 1, 1024, 0x21c6e6c4
0, 0, 0, 1, 1024, 0xbb5cde01

2
tests/ref/fate/filter-palettegen-2
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@@ -3,4 +3,4 @@
#codec_id 0: rawvideo
#dimensions 0: 16x16
#sar 0: 1/1
0, 0, 0, 1, 1024, 0x630d76b1
0, 0, 0, 1, 1024, 0xfbf66e70