libavfilter/edge_common.c

/*
 * 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
 */

#include "edge_common.h"

// Internal helper for ff_sobel()
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;
}

#undef DEPTH
#define DEPTH 8
#include "edge_template.c"

#undef DEPTH
#define DEPTH 16
#include "edge_template.c"

// Filters rounded gradients to drop all non-maxima
// Expects gradients generated by ff_sobel()
// Expects zero's destination buffer
void ff_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;
            }
        }
    }
}

// Filter to keep all pixels > high, and keep all pixels > low where all surrounding pixels > high
void ff_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;
    }
}