lavfi: add histeq filter

This is a port of virtual dub's histogram equalization filter by Donald
A. Graft. Based on the work by Jérémy Tran <tran.jeremy.av@gmail.com>,
done for SOCIS 2012.

Changelog

@@ -56,6 +56,7 @@ version <next>:
 - data: URI scheme
 - support building on the Plan 9 operating system
 - kerndeint filter ported from MPlayer
+- histeq filter ported from VirtualDub
 
 
 version 1.0:

LICENSE

@@ -31,6 +31,7 @@ Specifically, the GPL parts of FFmpeg are
     - vf_decimate.c
     - vf_delogo.c
     - vf_geq.c
+    - vf_histeq.c
     - vf_hqdn3d.c
     - vf_hue.c
     - vf_kerndeint.c

configure

@@ -1985,6 +1985,7 @@ frei0r_filter_extralibs='$ldl'
 frei0r_src_filter_deps="frei0r dlopen"
 frei0r_src_filter_extralibs='$ldl'
 geq_filter_deps="gpl"
+histeq_filter_deps="gpl"
 hqdn3d_filter_deps="gpl"
 hue_filter_deps="gpl"
 kerndeint_filter_deps="gpl"

doc/filters.texi

@@ -2664,6 +2664,44 @@ For example to horizontally flip the input video with @command{ffmpeg}:
 ffmpeg -i in.avi -vf "hflip" out.avi
 @end example
 
+@section histeq
+This filter applies a global color histogram equalization on a
+per-frame basis.
+
+It can be used to correct video that has a compressed range of pixel
+intensities.  The filter redistributes the pixel intensities to
+equalize their distribution across the intensity range. It may be
+viewed as an "automatically adjusting contrast filter". This filter is
+useful only for correcting degraded or poorly captured source
+video.
+
+The filter accepts parameters as a list of @var{key}=@var{value}
+pairs, separated by ":". If the key of the first options is omitted,
+the arguments are interpreted according to syntax
+@var{strength}:@var{intensity}:@var{antibanding}.
+
+This filter accepts the following named options:
+
+@table @option
+@item strength
+Determine the amount of equalization to be applied.  As the strength
+is reduced, the distribution of pixel intensities more-and-more
+approaches that of the input frame. The value must be a float number
+in the range [0,1] and defaults to 0.200.
+
+@item intensity
+Set the maximum intensity that can generated and scale the output
+values appropriately.  The strength should be set as desired and then
+the intensity can be limited if needed to avoid washing-out. The value
+must be a float number in the range [0,1] and defaults to 0.210.
+
+@item antibanding
+Set the antibanding level. If enabled the filter will randomly vary
+the luminance of output pixels by a small amount to avoid banding of
+the histogram. Possible values are @code{none}, @code{weak} or
+@code{strong}. It defaults to @code{none}.
+@end table
+
 @section hqdn3d
 
 High precision/quality 3d denoise filter. This filter aims to reduce

libavfilter/Makefile

@@ -111,6 +111,7 @@ OBJS-$(CONFIG_FREI0R_FILTER)                 += vf_frei0r.o
 OBJS-$(CONFIG_GEQ_FILTER)                    += vf_geq.o
 OBJS-$(CONFIG_GRADFUN_FILTER)                += vf_gradfun.o
 OBJS-$(CONFIG_HFLIP_FILTER)                  += vf_hflip.o
+OBJS-$(CONFIG_HISTEQ_FILTER)                 += vf_histeq.o
 OBJS-$(CONFIG_HQDN3D_FILTER)                 += vf_hqdn3d.o
 OBJS-$(CONFIG_HUE_FILTER)                    += vf_hue.o
 OBJS-$(CONFIG_IDET_FILTER)                   += vf_idet.o

libavfilter/allfilters.c

@@ -105,6 +105,7 @@ void avfilter_register_all(void)
     REGISTER_FILTER(GEQ,            geq,            vf);
     REGISTER_FILTER(GRADFUN,        gradfun,        vf);
     REGISTER_FILTER(HFLIP,          hflip,          vf);
+    REGISTER_FILTER(HISTEQ,         histeq,         vf);
     REGISTER_FILTER(HQDN3D,         hqdn3d,         vf);
     REGISTER_FILTER(HUE,            hue,            vf);
     REGISTER_FILTER(IDET,           idet,           vf);

libavfilter/version.h

@@ -29,7 +29,7 @@
 #include "libavutil/avutil.h"
 
 #define LIBAVFILTER_VERSION_MAJOR  3
-#define LIBAVFILTER_VERSION_MINOR  31
+#define LIBAVFILTER_VERSION_MINOR  32
 #define LIBAVFILTER_VERSION_MICRO 100
 
 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \

libavfilter/vf_histeq.c

@@ -0,0 +1,298 @@
+/*
+ * Copyright (c) 2012 Jeremy Tran
+ * Copyright (c) 2001 Donald A. Graft
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg 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.
+ *
+ * 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU 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
+ * Histogram equalization filter, based on the VirtualDub filter by
+ * Donald A. Graft  <neuron2 AT home DOT com>.
+ * Implements global automatic contrast adjustment by means of
+ * histogram equalization.
+ */
+
+#include "libavutil/common.h"
+#include "libavutil/opt.h"
+#include "libavutil/pixdesc.h"
+
+#include "avfilter.h"
+#include "drawutils.h"
+#include "formats.h"
+#include "internal.h"
+#include "video.h"
+
+// #define DEBUG
+
+// Linear Congruential Generator, see "Numerical Recipes"
+#define LCG_A 4096
+#define LCG_C 150889
+#define LCG_M 714025
+#define LCG(x) (((x) * LCG_A + LCG_C) % LCG_M)
+#define LCG_SEED 739187
+
+enum HisteqAntibanding {
+    HISTEQ_ANTIBANDING_NONE   = 0,
+    HISTEQ_ANTIBANDING_WEAK   = 1,
+    HISTEQ_ANTIBANDING_STRONG = 2,
+    HISTEQ_ANTIBANDING_NB,
+};
+
+typedef struct {
+    const AVClass *class;
+    float strength;
+    float intensity;
+    enum HisteqAntibanding antibanding;
+    char* antibanding_str;
+    int in_histogram [256];        ///< input histogram
+    int out_histogram[256];        ///< output histogram
+    int LUT[256];                  ///< lookup table derived from histogram[]
+    uint8_t rgba_map[4];           ///< components position
+    int bpp;                       ///< bytes per pixel
+} HisteqContext;
+
+#define OFFSET(x) offsetof(HisteqContext, x)
+#define FLAGS AV_OPT_FLAG_VIDEO_PARAM|AV_OPT_FLAG_FILTERING_PARAM
+#define CONST(name, help, val, unit) { name, help, 0, AV_OPT_TYPE_CONST, {.i64=val}, INT_MIN, INT_MAX, FLAGS, unit }
+
+static const AVOption histeq_options[] = {
+    { "strength",    "set the strength", OFFSET(strength), AV_OPT_TYPE_FLOAT, {.dbl=0.2}, 0, 1, FLAGS },
+    { "intensity",   "set the intensity", OFFSET(intensity), AV_OPT_TYPE_FLOAT, {.dbl=0.21}, 0, 1, FLAGS },
+    { "antibanding", "set the antibanding level", OFFSET(antibanding), AV_OPT_TYPE_INT, {.i64=HISTEQ_ANTIBANDING_NONE}, 0, HISTEQ_ANTIBANDING_NB-1, FLAGS, "antibanding" },
+    CONST("none",    "apply no antibanding",     HISTEQ_ANTIBANDING_NONE,   "antibanding"),
+    CONST("weak",    "apply weak antibanding",   HISTEQ_ANTIBANDING_WEAK,   "antibanding"),
+    CONST("strong",  "apply strong antibanding", HISTEQ_ANTIBANDING_STRONG, "antibanding"),
+    { NULL }
+};
+
+AVFILTER_DEFINE_CLASS(histeq);
+
+static av_cold int init(AVFilterContext *ctx, const char *args)
+{
+    HisteqContext *histeq = ctx->priv;
+    const char *shorthand[] = { "strength", "intensity", "antibanding", NULL };
+    int ret;
+
+    histeq->class = &histeq_class;
+    av_opt_set_defaults(histeq);
+
+    if ((ret = av_opt_set_from_string(histeq, args, shorthand, "=", ":")) < 0)
+        return ret;
+
+    av_log(ctx, AV_LOG_VERBOSE,
+           "strength:%0.3f intensity:%0.3f antibanding:%d\n",
+           histeq->strength, histeq->intensity, histeq->antibanding);
+
+    return 0;
+}
+
+static av_cold void uninit(AVFilterContext *ctx)
+{
+    HisteqContext *histeq = ctx->priv;
+    av_opt_free(histeq);
+}
+
+static int query_formats(AVFilterContext *ctx)
+{
+    static const enum PixelFormat pix_fmts[] = {
+        AV_PIX_FMT_ARGB, AV_PIX_FMT_RGBA, AV_PIX_FMT_ABGR, AV_PIX_FMT_BGRA,
+        AV_PIX_FMT_RGB24, AV_PIX_FMT_BGR24,
+        AV_PIX_FMT_NONE
+    };
+
+    ff_set_common_formats(ctx, ff_make_format_list(pix_fmts));
+    return 0;
+}
+
+static int config_input(AVFilterLink *inlink)
+{
+    AVFilterContext *ctx = inlink->dst;
+    HisteqContext *histeq = ctx->priv;
+    const AVPixFmtDescriptor *pix_desc = av_pix_fmt_desc_get(inlink->format);
+
+    histeq->bpp = av_get_bits_per_pixel(pix_desc) / 8;
+    ff_fill_rgba_map(histeq->rgba_map, inlink->format);
+
+    return 0;
+}
+
+#define R 0
+#define G 1
+#define B 2
+#define A 3
+
+#define GET_RGB_VALUES(r, g, b, src, map) do { \
+    r = src[x + map[R]];                       \
+    g = src[x + map[G]];                       \
+    b = src[x + map[B]];                       \
+} while (0)
+
+static int filter_frame(AVFilterLink *inlink, AVFilterBufferRef *inpic)
+{
+    AVFilterContext   *ctx     = inlink->dst;
+    HisteqContext     *histeq  = ctx->priv;
+    AVFilterLink      *outlink = ctx->outputs[0];
+    int strength  = histeq->strength  * 1000;
+    int intensity = histeq->intensity * 1000;
+    int x, y, i, luthi, lutlo, lut, luma, oluma, m;
+    AVFilterBufferRef *outpic;
+    unsigned int r, g, b, jran;
+    uint8_t *src, *dst;
+
+    outpic = ff_get_video_buffer(outlink, AV_PERM_WRITE|AV_PERM_ALIGN, outlink->w, outlink->h);
+    if (!outpic) {
+        avfilter_unref_bufferp(&inpic);
+        return AVERROR(ENOMEM);
+    }
+    avfilter_copy_buffer_ref_props(outpic, inpic);
+
+    /* Seed random generator for antibanding. */
+    jran = LCG_SEED;
+
+    /* Calculate and store the luminance and calculate the global histogram
+       based on the luminance. */
+    memset(histeq->in_histogram, 0, sizeof(histeq->in_histogram));
+    src = inpic->data[0];
+    dst = outpic->data[0];
+    for (y = 0; y < inlink->h; y++) {
+        for (x = 0; x < inlink->w * histeq->bpp; x += histeq->bpp) {
+            GET_RGB_VALUES(r, g, b, src, histeq->rgba_map);
+            luma = (55 * r + 182 * g + 19 * b) >> 8;
+            dst[x + histeq->rgba_map[A]] = luma;
+            histeq->in_histogram[luma]++;
+        }
+        src += inpic->linesize[0];
+        dst += outpic->linesize[0];
+    }
+
+#ifdef DEBUG
+    for (x = 0; x < 256; x++)
+        av_dlog(ctx, "in[%d]: %u\n", x, histeq->in_histogram[x]);
+#endif
+
+    /* Calculate the lookup table. */
+    histeq->LUT[0] = histeq->in_histogram[0];
+    /* Accumulate */
+    for (x = 1; x < 256; x++)
+        histeq->LUT[x] = histeq->LUT[x-1] + histeq->in_histogram[x];
+
+    /* Normalize */
+    for (x = 0; x < 256; x++)
+        histeq->LUT[x] = (histeq->LUT[x] * intensity) / (inlink->h * inlink->w);
+
+    /* Adjust the LUT based on the selected strength. This is an alpha
+       mix of the calculated LUT and a linear LUT with gain 1. */
+    for (x = 0; x < 256; x++)
+        histeq->LUT[x] = (strength * histeq->LUT[x]) / 255 +
+                         ((255 - strength) * x)      / 255;
+
+    /* Output the equalized frame. */
+    memset(histeq->out_histogram, 0, sizeof(histeq->out_histogram));
+
+    src = inpic->data[0];
+    dst = outpic->data[0];
+    for (y = 0; y < inlink->h; y++) {
+        for (x = 0; x < inlink->w * histeq->bpp; x += histeq->bpp) {
+            luma = dst[x + histeq->rgba_map[A]];
+            if (luma == 0) {
+                for (i = 0; i < histeq->bpp; ++i)
+                    dst[x + i] = 0;
+                histeq->out_histogram[0]++;
+            } else {
+                lut = histeq->LUT[luma];
+                if (histeq->antibanding != HISTEQ_ANTIBANDING_NONE) {
+                    if (luma > 0) {
+                        lutlo = histeq->antibanding == HISTEQ_ANTIBANDING_WEAK ?
+                                (histeq->LUT[luma] + histeq->LUT[luma - 1]) / 2 :
+                                 histeq->LUT[luma - 1];
+                    } else
+                        lutlo = lut;
+
+                    if (luma < 255) {
+                        luthi = (histeq->antibanding == HISTEQ_ANTIBANDING_WEAK) ?
+                            (histeq->LUT[luma] + histeq->LUT[luma + 1]) / 2 :
+                             histeq->LUT[luma + 1];
+                    } else
+                        luthi = lut;
+
+                    if (lutlo != luthi) {
+                        jran = LCG(jran);
+                        lut = lutlo + ((luthi - lutlo + 1) * jran) / LCG_M;
+                    }
+                }
+
+                GET_RGB_VALUES(r, g, b, src, histeq->rgba_map);
+                if (((m = FFMAX3(r, g, b)) * lut) / luma > 255) {
+                    r = (r * 255) / m;
+                    g = (g * 255) / m;
+                    b = (b * 255) / m;
+                } else {
+                    r = (r * lut) / luma;
+                    g = (g * lut) / luma;
+                    b = (b * lut) / luma;
+                }
+                dst[x + histeq->rgba_map[R]] = r;
+                dst[x + histeq->rgba_map[G]] = g;
+                dst[x + histeq->rgba_map[B]] = b;
+                oluma = (55 * r + 182 * g + 19 * b) >> 8;
+                histeq->out_histogram[oluma]++;
+            }
+        }
+        src += inpic->linesize[0];
+        dst += outpic->linesize[0];
+    }
+#ifdef DEBUG
+    for (x = 0; x < 256; x++)
+        av_dlog(ctx, "out[%d]: %u\n", x, histeq->out_histogram[x]);
+#endif
+
+    avfilter_unref_bufferp(&inpic);
+    return ff_filter_frame(outlink, outpic);
+}
+
+static const AVFilterPad histeq_inputs[] = {
+    {
+        .name             = "default",
+        .type             = AVMEDIA_TYPE_VIDEO,
+        .config_props     = config_input,
+        .filter_frame     = filter_frame,
+        .min_perms        = AV_PERM_READ,
+    },
+    { NULL }
+};
+
+static const AVFilterPad histeq_outputs[] = {
+    {
+        .name             = "default",
+        .type             = AVMEDIA_TYPE_VIDEO,
+    },
+    { NULL }
+};
+
+AVFilter avfilter_vf_histeq = {
+    .name          = "histeq",
+    .description   = NULL_IF_CONFIG_SMALL("Apply global color histogram equalization."),
+    .priv_size     = sizeof(HisteqContext),
+    .init          = init,
+    .uninit        = uninit,
+    .query_formats = query_formats,
+
+    .inputs        = histeq_inputs,
+    .outputs       = histeq_outputs,
+    .priv_class    = &histeq_class,
+};

tests/fate/avfilter.mak

@@ -41,6 +41,7 @@ FATE_LAVFI = fate-lavfi-alphaextract_rgb                                \
 
 FATE_LAVFI-$(CONFIG_GPL) += fate-lavfi-colormatrix1                     \
                             fate-lavfi-colormatrix2                     \
+                            fate-lavfi-histeq                           \
                             fate-lavfi-hue                              \
                             fate-lavfi-pixfmts_super2xsai               \
                             fate-lavfi-tinterlace_merge                 \

tests/lavfi-regression.sh

@@ -105,6 +105,7 @@ do_lavfi_pixfmts(){
 
 # all these filters have exactly one input and exactly one output
 do_lavfi_pixfmts "field"               "field"   "bottom"
+do_lavfi_pixfmts "histeq"              "histeq"  "antibanding=strong"
 do_lavfi_pixfmts "kerndeint"           "kerndeint" "" "tinterlace=interleave_top,"
 do_lavfi_pixfmts "pixfmts_copy"        "copy"    ""
 do_lavfi_pixfmts "pixfmts_crop"        "crop"    "100:100:100:100"

tests/ref/lavfi/histeq

@@ -0,0 +1,6 @@
+abgr                a538e1221c94a12fb4e60b47b5358f67
+argb                d0ef008d603d67a6a7d698d2a8f53d6a
+bgr24               9ef3c69a658490c4fbc807272372e73a
+bgra                716e70fdf7413d9a3b83e0365c2b0a99
+rgb24               8423322bbc66bc5050f6b93fdab23433
+rgba                a960c9423bbb3925c3511362348b38e2