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FFmpeg/libavfilter/vf_edgedetect.c
Valery Kot 855d51bf48 avfilter/vf_edgedetect: properly implement double_threshold() 
Important part of this algorithm is the double threshold step: pixels
above "high" threshold being kept, pixels below "low" threshold dropped,
pixels in between (weak edges) are kept if they are neighboring "high"
pixels.

The weak edge check uses a neighboring context and should not be applied
on the plane's border. The condition was incorrect and has been fixed in
the commit.

Signed-off-by: Andriy Gelman <andriy.gelman@gmail.com>
Reviewed-by: Andriy Gelman <andriy.gelman@gmail.com>
2020-07-06 23:20:53 -04:00

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/*
* Copyright (c) 2012-2014 Clément Bœsch <u pkh me>
*
* 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
* Edge detection filter
*
* @see https://en.wikipedia.org/wiki/Canny_edge_detector
*/
#include "libavutil/avassert.h"
#include "libavutil/imgutils.h"
#include "libavutil/opt.h"
#include "avfilter.h"
#include "formats.h"
#include "internal.h"
#include "video.h"
#define PLANE_R 0x4
#define PLANE_G 0x1
#define PLANE_B 0x2
#define PLANE_Y 0x1
#define PLANE_U 0x2
#define PLANE_V 0x4
#define PLANE_A 0x8
enum FilterMode {
MODE_WIRES,
MODE_COLORMIX,
MODE_CANNY,
NB_MODE
};
struct plane_info {
uint8_t *tmpbuf;
uint16_t *gradients;
char *directions;
int width, height;
};
typedef struct EdgeDetectContext {
const AVClass *class;
struct plane_info planes[3];
int filter_planes;
int nb_planes;
double low, high;
uint8_t low_u8, high_u8;
int mode;
} EdgeDetectContext;
#define OFFSET(x) offsetof(EdgeDetectContext, x)
#define FLAGS AV_OPT_FLAG_FILTERING_PARAM|AV_OPT_FLAG_VIDEO_PARAM
static const AVOption edgedetect_options[] = {
{ "high", "set high threshold", OFFSET(high), AV_OPT_TYPE_DOUBLE, {.dbl=50/255.}, 0, 1, FLAGS },
{ "low", "set low threshold", OFFSET(low), AV_OPT_TYPE_DOUBLE, {.dbl=20/255.}, 0, 1, FLAGS },
{ "mode", "set mode", OFFSET(mode), AV_OPT_TYPE_INT, {.i64=MODE_WIRES}, 0, NB_MODE-1, FLAGS, "mode" },
{ "wires", "white/gray wires on black", 0, AV_OPT_TYPE_CONST, {.i64=MODE_WIRES}, INT_MIN, INT_MAX, FLAGS, "mode" },
{ "colormix", "mix colors", 0, AV_OPT_TYPE_CONST, {.i64=MODE_COLORMIX}, INT_MIN, INT_MAX, FLAGS, "mode" },
{ "canny", "detect edges on planes", 0, AV_OPT_TYPE_CONST, {.i64=MODE_CANNY}, INT_MIN, INT_MAX, FLAGS, "mode" },
{ "planes", "set planes to filter", OFFSET(filter_planes), AV_OPT_TYPE_FLAGS, {.i64=7}, 1, 0x7, FLAGS, "flags" },
{ "y", "filter luma plane", 0, AV_OPT_TYPE_CONST, {.i64=PLANE_Y}, 0, 0, FLAGS, "flags" },
{ "u", "filter u plane", 0, AV_OPT_TYPE_CONST, {.i64=PLANE_U}, 0, 0, FLAGS, "flags" },
{ "v", "filter v plane", 0, AV_OPT_TYPE_CONST, {.i64=PLANE_V}, 0, 0, FLAGS, "flags" },
{ "r", "filter red plane", 0, AV_OPT_TYPE_CONST, {.i64=PLANE_R}, 0, 0, FLAGS, "flags" },
{ "g", "filter green plane", 0, AV_OPT_TYPE_CONST, {.i64=PLANE_G}, 0, 0, FLAGS, "flags" },
{ "b", "filter blue plane", 0, AV_OPT_TYPE_CONST, {.i64=PLANE_B}, 0, 0, FLAGS, "flags" },
{ NULL }
};
AVFILTER_DEFINE_CLASS(edgedetect);
static av_cold int init(AVFilterContext *ctx)
{
EdgeDetectContext *edgedetect = ctx->priv;
edgedetect->low_u8 = edgedetect->low * 255. + .5;
edgedetect->high_u8 = edgedetect->high * 255. + .5;
return 0;
}
static int query_formats(AVFilterContext *ctx)
{
const EdgeDetectContext *edgedetect = ctx->priv;
static const enum AVPixelFormat wires_pix_fmts[] = {AV_PIX_FMT_GRAY8, AV_PIX_FMT_NONE};
static const enum AVPixelFormat canny_pix_fmts[] = {AV_PIX_FMT_YUV420P, AV_PIX_FMT_YUV422P, AV_PIX_FMT_YUV444P, AV_PIX_FMT_GBRP, AV_PIX_FMT_GRAY8, AV_PIX_FMT_NONE};
static const enum AVPixelFormat colormix_pix_fmts[] = {AV_PIX_FMT_GBRP, AV_PIX_FMT_GRAY8, AV_PIX_FMT_NONE};
AVFilterFormats *fmts_list;
const enum AVPixelFormat *pix_fmts = NULL;
if (edgedetect->mode == MODE_WIRES) {
pix_fmts = wires_pix_fmts;
} else if (edgedetect->mode == MODE_COLORMIX) {
pix_fmts = colormix_pix_fmts;
} else if (edgedetect->mode == MODE_CANNY) {
pix_fmts = canny_pix_fmts;
} else {
av_assert0(0);
}
fmts_list = ff_make_format_list(pix_fmts);
if (!fmts_list)
return AVERROR(ENOMEM);
return ff_set_common_formats(ctx, fmts_list);
}
static int config_props(AVFilterLink *inlink)
{
int p;
AVFilterContext *ctx = inlink->dst;
EdgeDetectContext *edgedetect = ctx->priv;
const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(inlink->format);
edgedetect->nb_planes = inlink->format == AV_PIX_FMT_GRAY8 ? 1 : 3;
for (p = 0; p < edgedetect->nb_planes; p++) {
struct plane_info *plane = &edgedetect->planes[p];
int vsub = p ? desc->log2_chroma_h : 0;
int hsub = p ? desc->log2_chroma_w : 0;
plane->width = AV_CEIL_RSHIFT(inlink->w, hsub);
plane->height = AV_CEIL_RSHIFT(inlink->h, vsub);
plane->tmpbuf = av_malloc(plane->width * plane->height);
plane->gradients = av_calloc(plane->width * plane->height, sizeof(*plane->gradients));
plane->directions = av_malloc(plane->width * plane->height);
if (!plane->tmpbuf || !plane->gradients || !plane->directions)
return AVERROR(ENOMEM);
}
return 0;
}
static void gaussian_blur(AVFilterContext *ctx, int w, int h,
uint8_t *dst, int dst_linesize,
const uint8_t *src, int src_linesize)
{
int i, j;
memcpy(dst, src, w); dst += dst_linesize; src += src_linesize;
if (h > 1) {
memcpy(dst, src, w); dst += dst_linesize; src += src_linesize;
}
for (j = 2; j < h - 2; j++) {
dst[0] = src[0];
if (w > 1)
dst[1] = src[1];
for (i = 2; i < w - 2; i++) {
/* Gaussian mask of size 5x5 with sigma = 1.4 */
dst[i] = ((src[-2*src_linesize + i-2] + src[2*src_linesize + i-2]) * 2
+ (src[-2*src_linesize + i-1] + src[2*src_linesize + i-1]) * 4
+ (src[-2*src_linesize + i ] + src[2*src_linesize + i ]) * 5
+ (src[-2*src_linesize + i+1] + src[2*src_linesize + i+1]) * 4
+ (src[-2*src_linesize + i+2] + src[2*src_linesize + i+2]) * 2
+ (src[ -src_linesize + i-2] + src[ src_linesize + i-2]) * 4
+ (src[ -src_linesize + i-1] + src[ src_linesize + i-1]) * 9
+ (src[ -src_linesize + i ] + src[ src_linesize + i ]) * 12
+ (src[ -src_linesize + i+1] + src[ src_linesize + i+1]) * 9
+ (src[ -src_linesize + i+2] + src[ src_linesize + i+2]) * 4
+ src[i-2] * 5
+ src[i-1] * 12
+ src[i ] * 15
+ src[i+1] * 12
+ src[i+2] * 5) / 159;
}
if (w > 2)
dst[i ] = src[i ];
if (w > 3)
dst[i + 1] = src[i + 1];
dst += dst_linesize;
src += src_linesize;
}
if (h > 2) {
memcpy(dst, src, w); dst += dst_linesize; src += src_linesize;
}
if (h > 3)
memcpy(dst, src, w);
}
enum {
DIRECTION_45UP,
DIRECTION_45DOWN,
DIRECTION_HORIZONTAL,
DIRECTION_VERTICAL,
};
static int get_rounded_direction(int gx, int gy)
{
/* reference angles:
* tan( pi/8) = sqrt(2)-1
* tan(3pi/8) = sqrt(2)+1
* Gy/Gx is the tangent of the angle (theta), so Gy/Gx is compared against
* <ref-angle>, or more simply Gy against <ref-angle>*Gx
*
* Gx and Gy bounds = [-1020;1020], using 16-bit arithmetic:
* round((sqrt(2)-1) * (1<<16)) = 27146
* round((sqrt(2)+1) * (1<<16)) = 158218
*/
if (gx) {
int tanpi8gx, tan3pi8gx;
if (gx < 0)
gx = -gx, gy = -gy;
gy *= (1 << 16);
tanpi8gx = 27146 * gx;
tan3pi8gx = 158218 * gx;
if (gy > -tan3pi8gx && gy < -tanpi8gx) return DIRECTION_45UP;
if (gy > -tanpi8gx && gy < tanpi8gx) return DIRECTION_HORIZONTAL;
if (gy > tanpi8gx && gy < tan3pi8gx) return DIRECTION_45DOWN;
}
return DIRECTION_VERTICAL;
}
static void sobel(int w, int h,
uint16_t *dst, int dst_linesize,
int8_t *dir, int dir_linesize,
const uint8_t *src, int src_linesize)
{
int i, j;
for (j = 1; j < h - 1; j++) {
dst += dst_linesize;
dir += dir_linesize;
src += src_linesize;
for (i = 1; i < w - 1; i++) {
const int gx =
-1*src[-src_linesize + i-1] + 1*src[-src_linesize + i+1]
-2*src[ i-1] + 2*src[ i+1]
-1*src[ src_linesize + i-1] + 1*src[ src_linesize + i+1];
const int gy =
-1*src[-src_linesize + i-1] + 1*src[ src_linesize + i-1]
-2*src[-src_linesize + i ] + 2*src[ src_linesize + i ]
-1*src[-src_linesize + i+1] + 1*src[ src_linesize + i+1];
dst[i] = FFABS(gx) + FFABS(gy);
dir[i] = get_rounded_direction(gx, gy);
}
}
}
static void non_maximum_suppression(int w, int h,
uint8_t *dst, int dst_linesize,
const int8_t *dir, int dir_linesize,
const uint16_t *src, int src_linesize)
{
int i, j;
#define COPY_MAXIMA(ay, ax, by, bx) do { \
if (src[i] > src[(ay)*src_linesize + i+(ax)] && \
src[i] > src[(by)*src_linesize + i+(bx)]) \
dst[i] = av_clip_uint8(src[i]); \
} while (0)
for (j = 1; j < h - 1; j++) {
dst += dst_linesize;
dir += dir_linesize;
src += src_linesize;
for (i = 1; i < w - 1; i++) {
switch (dir[i]) {
case DIRECTION_45UP: COPY_MAXIMA( 1, -1, -1, 1); break;
case DIRECTION_45DOWN: COPY_MAXIMA(-1, -1, 1, 1); break;
case DIRECTION_HORIZONTAL: COPY_MAXIMA( 0, -1, 0, 1); break;
case DIRECTION_VERTICAL: COPY_MAXIMA(-1, 0, 1, 0); break;
}
}
}
}
static void double_threshold(int low, int high, int w, int h,
uint8_t *dst, int dst_linesize,
const uint8_t *src, int src_linesize)
{
int i, j;
for (j = 0; j < h; j++) {
for (i = 0; i < w; i++) {
if (src[i] > high) {
dst[i] = src[i];
continue;
}
if (!(!i || i == w - 1 || !j || j == h - 1) &&
src[i] > low &&
(src[-src_linesize + i-1] > high ||
src[-src_linesize + i ] > high ||
src[-src_linesize + i+1] > high ||
src[ i-1] > high ||
src[ i+1] > high ||
src[ src_linesize + i-1] > high ||
src[ src_linesize + i ] > high ||
src[ src_linesize + i+1] > high))
dst[i] = src[i];
else
dst[i] = 0;
}
dst += dst_linesize;
src += src_linesize;
}
}
static void color_mix(int w, int h,
uint8_t *dst, int dst_linesize,
const uint8_t *src, int src_linesize)
{
int i, j;
for (j = 0; j < h; j++) {
for (i = 0; i < w; i++)
dst[i] = (dst[i] + src[i]) >> 1;
dst += dst_linesize;
src += src_linesize;
}
}
static int filter_frame(AVFilterLink *inlink, AVFrame *in)
{
AVFilterContext *ctx = inlink->dst;
EdgeDetectContext *edgedetect = ctx->priv;
AVFilterLink *outlink = ctx->outputs[0];
int p, direct = 0;
AVFrame *out;
if (edgedetect->mode != MODE_COLORMIX && av_frame_is_writable(in)) {
direct = 1;
out = in;
} else {
out = ff_get_video_buffer(outlink, outlink->w, outlink->h);
if (!out) {
av_frame_free(&in);
return AVERROR(ENOMEM);
}
av_frame_copy_props(out, in);
}
for (p = 0; p < edgedetect->nb_planes; p++) {
struct plane_info *plane = &edgedetect->planes[p];
uint8_t *tmpbuf = plane->tmpbuf;
uint16_t *gradients = plane->gradients;
int8_t *directions = plane->directions;
const int width = plane->width;
const int height = plane->height;
if (!((1 << p) & edgedetect->filter_planes)) {
if (!direct)
av_image_copy_plane(out->data[p], out->linesize[p],
in->data[p], in->linesize[p],
width, height);
continue;
}
/* gaussian filter to reduce noise */
gaussian_blur(ctx, width, height,
tmpbuf, width,
in->data[p], in->linesize[p]);
/* compute the 16-bits gradients and directions for the next step */
sobel(width, height,
gradients, width,
directions,width,
tmpbuf, width);
/* non_maximum_suppression() will actually keep & clip what's necessary and
* ignore the rest, so we need a clean output buffer */
memset(tmpbuf, 0, width * height);
non_maximum_suppression(width, height,
tmpbuf, width,
directions,width,
gradients, width);
/* keep high values, or low values surrounded by high values */
double_threshold(edgedetect->low_u8, edgedetect->high_u8,
width, height,
out->data[p], out->linesize[p],
tmpbuf, width);
if (edgedetect->mode == MODE_COLORMIX) {
color_mix(width, height,
out->data[p], out->linesize[p],
in->data[p], in->linesize[p]);
}
}
if (!direct)
av_frame_free(&in);
return ff_filter_frame(outlink, out);
}
static av_cold void uninit(AVFilterContext *ctx)
{
int p;
EdgeDetectContext *edgedetect = ctx->priv;
for (p = 0; p < edgedetect->nb_planes; p++) {
struct plane_info *plane = &edgedetect->planes[p];
av_freep(&plane->tmpbuf);
av_freep(&plane->gradients);
av_freep(&plane->directions);
}
}
static const AVFilterPad edgedetect_inputs[] = {
{
.name = "default",
.type = AVMEDIA_TYPE_VIDEO,
.config_props = config_props,
.filter_frame = filter_frame,
},
{ NULL }
};
static const AVFilterPad edgedetect_outputs[] = {
{
.name = "default",
.type = AVMEDIA_TYPE_VIDEO,
},
{ NULL }
};
AVFilter ff_vf_edgedetect = {
.name = "edgedetect",
.description = NULL_IF_CONFIG_SMALL("Detect and draw edge."),
.priv_size = sizeof(EdgeDetectContext),
.init = init,
.uninit = uninit,
.query_formats = query_formats,
.inputs = edgedetect_inputs,
.outputs = edgedetect_outputs,
.priv_class = &edgedetect_class,
.flags = AVFILTER_FLAG_SUPPORT_TIMELINE_GENERIC,
};
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