avfilter: add palettegen filter

doc/filters.texi

@@ -6909,6 +6909,51 @@ pad="2*iw:2*ih:ow-iw:oh-ih"
 @end example
 @end itemize
 
+@section palettegen
+
+Generate one palette for a whole video stream.
+
+It accepts the following options:
+
+@table @option
+@item max_colors
+Set the maximum number of colors to quantize in the palette.
+Note: the palette will still contain 256 colors; the unused palette entries
+will be black.
+
+@item reserve_transparent
+Create a palette of 255 colors maximum and reserve the last one for
+transparency. Reserving the transparency color is useful for GIF optimization.
+If not set, the maximum of colors in the palette will be 256. You probably want
+to disable this option for a standalone image.
+Set by default.
+
+@item stats_mode
+Set statistics mode.
+
+It accepts the following values:
+@table @samp
+@item full
+Compute full frame histograms.
+@item diff
+Compute histograms only for the part that differs from previous frame. This
+might be relevant to give more importance to the moving part of your input if
+the background is static.
+@end table
+
+Default value is @var{full}.
+@end table
+
+@subsection Examples
+
+@itemize
+@item
+Generate a representative palette of a given video using @command{ffmpeg}:
+@example
+ffmpeg -i input.mkv -vf palettegen palette.png
+@end example
+@end itemize
+
 @section perspective
 
 Correct perspective of video not recorded perpendicular to the screen.

libavfilter/Makefile

@@ -160,6 +160,7 @@ OBJS-$(CONFIG_OPENCL)                        += deshake_opencl.o unsharp_opencl.
 OBJS-$(CONFIG_OVERLAY_FILTER)                += vf_overlay.o dualinput.o framesync.o
 OBJS-$(CONFIG_OWDENOISE_FILTER)              += vf_owdenoise.o
 OBJS-$(CONFIG_PAD_FILTER)                    += vf_pad.o
+OBJS-$(CONFIG_PALETTEGEN_FILTER)             += vf_palettegen.o
 OBJS-$(CONFIG_PERMS_FILTER)                  += f_perms.o
 OBJS-$(CONFIG_PERSPECTIVE_FILTER)            += vf_perspective.o
 OBJS-$(CONFIG_PHASE_FILTER)                  += vf_phase.o

libavfilter/allfilters.c

@@ -175,6 +175,7 @@ void avfilter_register_all(void)
     REGISTER_FILTER(OVERLAY,        overlay,        vf);
     REGISTER_FILTER(OWDENOISE,      owdenoise,      vf);
     REGISTER_FILTER(PAD,            pad,            vf);
+    REGISTER_FILTER(PALETTEGEN,     palettegen,     vf);
     REGISTER_FILTER(PERMS,          perms,          vf);
     REGISTER_FILTER(PERSPECTIVE,    perspective,    vf);
     REGISTER_FILTER(PHASE,          phase,          vf);

libavfilter/vf_palettegen.c

@@ -0,0 +1,547 @@
+/*
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it 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.
+ *
+ * FFmpeg 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/**
+ * @file
+ * Generate one palette for a whole video stream.
+ */
+
+#include "libavutil/avassert.h"
+#include "libavutil/opt.h"
+#include "avfilter.h"
+#include "internal.h"
+
+/* Reference a color and how much it's used */
+struct color_ref {
+    uint32_t color;
+    uint64_t count;
+};
+
+/* Store a range of colors */
+struct range_box {
+    uint32_t color;     // average color
+    int64_t variance;   // overall variance of the box (how much the colors are spread)
+    int start;          // index in PaletteGenContext->refs
+    int len;            // number of referenced colors
+    int sorted_by;      // whether range of colors is sorted by red (0), green (1) or blue (2)
+};
+
+struct hist_node {
+    struct color_ref *entries;
+    int nb_entries;
+};
+
+enum {
+    STATS_MODE_ALL_FRAMES,
+    STATS_MODE_DIFF_FRAMES,
+    NB_STATS_MODE
+};
+
+#define NBITS 4
+#define HIST_SIZE (1<<(3*NBITS))
+
+typedef struct {
+    const AVClass *class;
+
+    int max_colors;
+    int reserve_transparent;
+    int stats_mode;
+
+    AVFrame *prev_frame;                    // previous frame used for the diff stats_mode
+    struct hist_node histogram[HIST_SIZE];  // histogram/hashtable of the colors
+    struct color_ref **refs;                // references of all the colors used in the stream
+    int nb_refs;                            // number of color references (or number of different colors)
+    struct range_box boxes[256];            // define the segmentation of the colorspace (the final palette)
+    int nb_boxes;                           // number of boxes (increase will segmenting them)
+    int palette_pushed;                     // if the palette frame is pushed into the outlink or not
+} PaletteGenContext;
+
+#define OFFSET(x) offsetof(PaletteGenContext, x)
+#define FLAGS AV_OPT_FLAG_FILTERING_PARAM|AV_OPT_FLAG_VIDEO_PARAM
+static const AVOption palettegen_options[] = {
+    { "max_colors", "set the maximum number of colors to use in the palette", OFFSET(max_colors), AV_OPT_TYPE_INT, {.i64=256}, 4, 256, FLAGS },
+    { "reserve_transparent", "reserve a palette entry for transparency", OFFSET(reserve_transparent), AV_OPT_TYPE_INT, {.i64=1}, 0, 1, FLAGS },
+    { "stats_mode", "set statistics mode", OFFSET(stats_mode), AV_OPT_TYPE_INT, {.i64=STATS_MODE_ALL_FRAMES}, 0, NB_STATS_MODE, FLAGS, "mode" },
+        { "full", "compute full frame histograms", 0, AV_OPT_TYPE_CONST, {.i64=STATS_MODE_ALL_FRAMES}, INT_MIN, INT_MAX, FLAGS, "mode" },
+        { "diff", "compute histograms only for the part that differs from previous frame", 0, AV_OPT_TYPE_CONST, {.i64=STATS_MODE_DIFF_FRAMES}, INT_MIN, INT_MAX, FLAGS, "mode" },
+    { NULL }
+};
+
+AVFILTER_DEFINE_CLASS(palettegen);
+
+static int query_formats(AVFilterContext *ctx)
+{
+    static const enum AVPixelFormat in_fmts[]  = {AV_PIX_FMT_RGB32, AV_PIX_FMT_NONE};
+    static const enum AVPixelFormat out_fmts[] = {AV_PIX_FMT_RGB32, AV_PIX_FMT_NONE};
+    AVFilterFormats *in  = ff_make_format_list(in_fmts);
+    AVFilterFormats *out = ff_make_format_list(out_fmts);
+    if (!in || !out)
+        return AVERROR(ENOMEM);
+    ff_formats_ref(in,  &ctx->inputs[0]->out_formats);
+    ff_formats_ref(out, &ctx->outputs[0]->in_formats);
+    return 0;
+}
+
+typedef int (*cmp_func)(const void *, const void *);
+
+#define DECLARE_CMP_FUNC(name, pos)                     \
+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   ((*a)->color >> (8 * (2 - (pos))) & 0xff)  \
+           - ((*b)->color >> (8 * (2 - (pos))) & 0xff); \
+}
+
+DECLARE_CMP_FUNC(r, 0)
+DECLARE_CMP_FUNC(g, 1)
+DECLARE_CMP_FUNC(b, 2)
+
+static const cmp_func cmp_funcs[] = {cmp_r, cmp_g, cmp_b};
+
+/**
+ * Simple color comparison for sorting the final palette
+ */
+static int cmp_color(const void *a, const void *b)
+{
+    const struct range_box *box1 = a;
+    const struct range_box *box2 = b;
+    return box1->color - box2->color;
+}
+
+static av_always_inline int diff(const uint32_t a, const uint32_t b)
+{
+    const uint8_t c1[] = {a >> 16 & 0xff, a >> 8 & 0xff, a & 0xff};
+    const uint8_t c2[] = {b >> 16 & 0xff, b >> 8 & 0xff, b & 0xff};
+    const int dr = c1[0] - c2[0];
+    const int dg = c1[1] - c2[1];
+    const int db = c1[2] - c2[2];
+    return dr*dr + dg*dg + db*db;
+}
+
+/**
+ * Find the next box to split: pick the one with the highest variance
+ */
+static int get_next_box_id_to_split(PaletteGenContext *s)
+{
+    int box_id, i, best_box_id = -1;
+    int64_t max_variance = -1;
+
+    if (s->nb_boxes == s->max_colors - s->reserve_transparent)
+        return -1;
+
+    for (box_id = 0; box_id < s->nb_boxes; box_id++) {
+        struct range_box *box = &s->boxes[box_id];
+
+        if (s->boxes[box_id].len >= 2) {
+
+            if (box->variance == -1) {
+                int64_t variance = 0;
+
+                for (i = 0; i < box->len; i++) {
+                    const struct color_ref *ref = s->refs[box->start + i];
+                    variance += diff(ref->color, box->color) * ref->count;
+                }
+                box->variance = variance;
+            }
+            if (box->variance > max_variance) {
+                best_box_id = box_id;
+                max_variance = box->variance;
+            }
+        } else {
+            box->variance = -1;
+        }
+    }
+    return best_box_id;
+}
+
+/**
+ * Get the 32-bit average color for the range of RGB colors enclosed in the
+ * specified box. Takes into account the weight of each color.
+ */
+static uint32_t get_avg_color(struct color_ref * const *refs,
+                              const struct range_box *box)
+{
+    int i;
+    const int n = box->len;
+    uint64_t r = 0, g = 0, b = 0, div = 0;
+
+    for (i = 0; i < n; i++) {
+        const struct color_ref *ref = refs[box->start + i];
+        r += (ref->color >> 16 & 0xff) * ref->count;
+        g += (ref->color >>  8 & 0xff) * ref->count;
+        b += (ref->color       & 0xff) * ref->count;
+        div += ref->count;
+    }
+
+    r = r / div;
+    g = g / div;
+    b = b / div;
+
+    return 0xffU<<24 | r<<16 | g<<8 | b;
+}
+
+/**
+ * Split given box in two at position n. The original box becomes the left part
+ * of the split, and the new index box is the right part.
+ */
+static void split_box(PaletteGenContext *s, struct range_box *box, int n)
+{
+    struct range_box *new_box = &s->boxes[s->nb_boxes++];
+    new_box->start     = n + 1;
+    new_box->len       = box->start + box->len - new_box->start;
+    new_box->sorted_by = box->sorted_by;
+    box->len -= new_box->len;
+
+    av_assert0(box->len     >= 1);
+    av_assert0(new_box->len >= 1);
+
+    box->color     = get_avg_color(s->refs, box);
+    new_box->color = get_avg_color(s->refs, new_box);
+    box->variance     = -1;
+    new_box->variance = -1;
+}
+
+/**
+ * Write the palette into the output frame.
+ */
+static void write_palette(const PaletteGenContext *s, AVFrame *out)
+{
+    int x, y, box_id = 0;
+    uint32_t *pal = (uint32_t *)out->data[0];
+    const int pal_linesize = out->linesize[0] >> 2;
+    uint32_t last_color = 0;
+
+    for (y = 0; y < out->height; y++) {
+        for (x = 0; x < out->width; x++) {
+            if (box_id < s->nb_boxes) {
+                pal[x] = s->boxes[box_id++].color;
+                if ((x || y) && pal[x] == last_color)
+                    av_log(NULL, AV_LOG_WARNING, "Dupped color: %08X\n", pal[x]);
+                last_color = pal[x];
+            } else {
+                pal[x] = 0xff000000; // pad with black
+            }
+        }
+        pal += pal_linesize;
+    }
+
+    if (s->reserve_transparent) {
+        av_assert0(s->nb_boxes < 256);
+        pal[out->width - pal_linesize - 1] = 0x0000ff00; // add a green transparent color
+    }
+}
+
+/**
+ * Crawl the histogram to get all the defined colors, and create a linear list
+ * of them (each color reference entry is a pointer to the value in the
+ * histogram/hash table).
+ */
+static struct color_ref **load_color_refs(const struct hist_node *hist, int nb_refs)
+{
+    int i, j, k = 0;
+    struct color_ref **refs = av_malloc_array(nb_refs, sizeof(*refs));
+
+    if (!refs)
+        return NULL;
+
+    for (j = 0; j < HIST_SIZE; j++) {
+        const struct hist_node *node = &hist[j];
+
+        for (i = 0; i < node->nb_entries; i++)
+            refs[k++] = &node->entries[i];
+    }
+
+    return refs;
+}
+
+/**
+ * Main function implementing the Median Cut Algorithm defined by Paul Heckbert
+ * in Color Image Quantization for Frame Buffer Display (1982)
+ */
+static AVFrame *get_palette_frame(AVFilterContext *ctx)
+{
+    AVFrame *out;
+    PaletteGenContext *s = ctx->priv;
+    AVFilterLink *outlink = ctx->outputs[0];
+    int box_id = 0;
+    int longest = 0;
+    struct range_box *box;
+
+    /* reference only the used colors from histogram */
+    s->refs = load_color_refs(s->histogram, s->nb_refs);
+    if (!s->refs) {
+        av_log(ctx, AV_LOG_ERROR, "Unable to allocate references for %d different colors\n", s->nb_refs);
+        return NULL;
+    }
+
+    /* create the palette frame */
+    out = ff_get_video_buffer(outlink, outlink->w, outlink->h);
+    if (!out)
+        return NULL;
+    out->pts = 0;
+
+    /* set first box for 0..nb_refs */
+    box = &s->boxes[box_id];
+    box->len = s->nb_refs;
+    box->sorted_by = -1;
+    box->color = get_avg_color(s->refs, box);
+    box->variance = -1;
+    s->nb_boxes = 1;
+
+    while (box && box->len > 1) {
+        int i, rr, gr, br;
+        uint64_t median, box_weight = 0;
+
+        /* compute the box weight (sum all the weights of the colors in the
+         * range) and its boundings */
+        uint8_t min[3] = {0xff, 0xff, 0xff};
+        uint8_t max[3] = {0x00, 0x00, 0x00};
+        for (i = box->start; i < box->start + box->len; i++) {
+            const struct color_ref *ref = s->refs[i];
+            const uint32_t rgb = ref->color;
+            const uint8_t r = rgb >> 16 & 0xff, g = rgb >> 8 & 0xff, b = rgb & 0xff;
+            min[0] = FFMIN(r, min[0]), max[0] = FFMAX(r, max[0]);
+            min[1] = FFMIN(g, min[1]), max[1] = FFMAX(g, max[1]);
+            min[2] = FFMIN(b, min[2]), max[2] = FFMAX(b, max[2]);
+            box_weight += ref->count;
+        }
+
+        /* define the axis to sort by according to the widest range of colors */
+        rr = max[0] - min[0];
+        gr = max[1] - min[1];
+        br = max[2] - min[2];
+        longest = 1; // pick green by default (the color the eye is the most sensitive to)
+        if (br >= rr && br >= gr) longest = 2;
+        if (rr >= gr && rr >= br) longest = 0;
+        if (gr >= rr && gr >= br) longest = 1; // prefer green again
+
+        av_dlog(ctx, "box #%02X [%6d..%-6d] (%6d) w:%-6"PRIu64" ranges:[%2x %2x %2x] sort by %c (already sorted:%c) ",
+                box_id, box->start, box->start + box->len - 1, box->len, box_weight,
+                rr, gr, br, "rgb"[longest], box->sorted_by == longest ? 'y':'n');
+
+        /* sort the range by its longest axis if it's not already sorted */
+        if (box->sorted_by != longest) {
+            qsort(&s->refs[box->start], box->len, sizeof(*s->refs), cmp_funcs[longest]);
+            box->sorted_by = longest;
+        }
+
+        /* locate the median where to split */
+        median = (box_weight + 1) >> 1;
+        box_weight = 0;
+        /* if you have 2 boxes, the maximum is actually #0: you must have at
+         * least 1 color on each side of the split, hence the -2 */
+        for (i = box->start; i < box->start + box->len - 2; i++) {
+            box_weight += s->refs[i]->count;
+            if (box_weight > median)
+                break;
+        }
+        av_dlog(ctx, "split @ i=%-6d with w=%-6"PRIu64" (target=%6"PRIu64")\n", i, box_weight, median);
+        split_box(s, box, i);
+
+        box_id = get_next_box_id_to_split(s);
+        box = box_id >= 0 ? &s->boxes[box_id] : NULL;
+    }
+
+    av_log(ctx, AV_LOG_DEBUG, "%d%s boxes generated out of %d colors\n",
+           s->nb_boxes, s->reserve_transparent ? "(+1)" : "", s->nb_refs);
+
+    qsort(s->boxes, s->nb_boxes, sizeof(*s->boxes), cmp_color);
+
+    write_palette(s, out);
+
+    return out;
+}
+
+/**
+ * Hashing function for the color.
+ * It keeps the NBITS least significant bit of each component to make it
+ * "random" even if the scene doesn't have much different colors.
+ */
+static inline unsigned color_hash(uint32_t color)
+{
+    const uint8_t r = color >> 16 & ((1<<NBITS)-1);
+    const uint8_t g = color >>  8 & ((1<<NBITS)-1);
+    const uint8_t b = color       & ((1<<NBITS)-1);
+    return r<<(NBITS*2) | g<<NBITS | b;
+}
+
+/**
+ * Locate the color in the hash table and increment its counter.
+ */
+static int color_inc(struct hist_node *hist, uint32_t color)
+{
+    int i;
+    const unsigned hash = color_hash(color);
+    struct hist_node *node = &hist[hash];
+    struct color_ref *e;
+
+    for (i = 0; i < node->nb_entries; i++) {
+        e = &node->entries[i];
+        if (e->color == color) {
+            e->count++;
+            return 0;
+        }
+    }
+
+    e = av_dynarray2_add((void**)&node->entries, &node->nb_entries,
+                         sizeof(*node->entries), NULL);
+    if (!e)
+        return AVERROR(ENOMEM);
+    e->color = color;
+    e->count = 1;
+    return 1;
+}
+
+/**
+ * Update histogram when pixels differ from previous frame.
+ */
+static int update_histogram_diff(struct hist_node *hist,
+                                 const AVFrame *f1, const AVFrame *f2)
+{
+    int x, y, ret, nb_diff_colors = 0;
+
+    for (y = 0; y < f1->height; y++) {
+        const uint32_t *p = (const uint32_t *)(f1->data[0] + y*f1->linesize[0]);
+        const uint32_t *q = (const uint32_t *)(f2->data[0] + y*f2->linesize[0]);
+
+        for (x = 0; x < f2->width; x++) {
+            if (p[x] == q[x])
+                continue;
+            ret = color_inc(hist, p[x]);
+            if (ret < 0)
+                return ret;
+            nb_diff_colors += ret;
+        }
+    }
+    return nb_diff_colors;
+}
+
+/**
+ * Simple histogram of the frame.
+ */
+static int update_histogram_frame(struct hist_node *hist, const AVFrame *f)
+{
+    int x, y, ret, nb_diff_colors = 0;
+
+    for (y = 0; y < f->height; y++) {
+        const uint32_t *p = (const uint32_t *)(f->data[0] + y*f->linesize[0]);
+
+        for (x = 0; x < f->width; x++) {
+            ret = color_inc(hist, p[x]);
+            if (ret < 0)
+                return ret;
+            nb_diff_colors += ret;
+        }
+    }
+    return nb_diff_colors;
+}
+
+/**
+ * Update the histogram for each passing frame. No frame will be pushed here.
+ */
+static int filter_frame(AVFilterLink *inlink, AVFrame *in)
+{
+    AVFilterContext *ctx = inlink->dst;
+    PaletteGenContext *s = ctx->priv;
+    const int ret = s->prev_frame ? update_histogram_diff(s->histogram, s->prev_frame, in)
+                                  : update_histogram_frame(s->histogram, in);
+
+    if (ret > 0)
+        s->nb_refs += ret;
+
+    if (s->stats_mode == STATS_MODE_DIFF_FRAMES) {
+        av_frame_free(&s->prev_frame);
+        s->prev_frame = in;
+    } else {
+        av_frame_free(&in);
+    }
+
+    return ret;
+}
+
+/**
+ * Returns only one frame at the end containing the full palette.
+ */
+static int request_frame(AVFilterLink *outlink)
+{
+    AVFilterContext *ctx = outlink->src;
+    AVFilterLink *inlink = ctx->inputs[0];
+    PaletteGenContext *s = ctx->priv;
+    int r;
+
+    r = ff_request_frame(inlink);
+    if (r == AVERROR_EOF && !s->palette_pushed) {
+        r = ff_filter_frame(outlink, get_palette_frame(ctx));
+        s->palette_pushed = 1;
+        return r;
+    }
+    return r;
+}
+
+/**
+ * The output is one simple 16x16 squared-pixels palette.
+ */
+static int config_output(AVFilterLink *outlink)
+{
+    outlink->w = outlink->h = 16;
+    outlink->sample_aspect_ratio = av_make_q(1, 1);
+    outlink->flags |= FF_LINK_FLAG_REQUEST_LOOP;
+    return 0;
+}
+
+static av_cold void uninit(AVFilterContext *ctx)
+{
+    int i;
+    PaletteGenContext *s = ctx->priv;
+
+    for (i = 0; i < HIST_SIZE; i++)
+        av_freep(&s->histogram[i].entries);
+    av_freep(&s->refs);
+    av_freep(&s->prev_frame);
+}
+
+static const AVFilterPad palettegen_inputs[] = {
+    {
+        .name         = "default",
+        .type         = AVMEDIA_TYPE_VIDEO,
+        .filter_frame = filter_frame,
+    },
+    { NULL }
+};
+
+static const AVFilterPad palettegen_outputs[] = {
+    {
+        .name          = "default",
+        .type          = AVMEDIA_TYPE_VIDEO,
+        .config_props  = config_output,
+        .request_frame = request_frame,
+    },
+    { NULL }
+};
+
+AVFilter ff_vf_palettegen = {
+    .name          = "palettegen",
+    .description   = NULL_IF_CONFIG_SMALL("Find the optimal palette for a given stream."),
+    .priv_size     = sizeof(PaletteGenContext),
+    .uninit        = uninit,
+    .query_formats = query_formats,
+    .inputs        = palettegen_inputs,
+    .outputs       = palettegen_outputs,
+    .priv_class    = &palettegen_class,
+};