[vlc-devel] [PATCH] Implemented a new edge detection video filter
Odd-Arild Kristensen
oddarildkristensen at gmail.com
Thu Feb 4 23:50:02 CET 2016
The edge detection filter uses the Sobel operator to detect and highlight edges in a frame. In order to successfully detect an edge, the image must first be converted to gray scale (because Sobel is a gray scale operator) and then have a slight Gaussian blur applied to it. We do this because Sobel is a noisy operator and the Gaussian blur reduces this noise.
---
modules/video_filter/Makefile.am | 3 +
modules/video_filter/edgedetection.c | 243 +++++++++++++++++++++++++++++++++++
2 files changed, 246 insertions(+)
create mode 100644 modules/video_filter/edgedetection.c
diff --git a/modules/video_filter/Makefile.am b/modules/video_filter/Makefile.am
index ea0b72c..b2ff9cd 100644
--- a/modules/video_filter/Makefile.am
+++ b/modules/video_filter/Makefile.am
@@ -3,6 +3,8 @@ video_filterdir = $(pluginsdir)/video_filter
noinst_HEADERS += video_filter/filter_picture.h
# video filters
+libedgedetection_plugin_la_SOURCES = video_filter/edgedetection.c
+libedgedetection_plugin_la_LIBADD = $(LIBM)
libadjust_plugin_la_SOURCES = video_filter/adjust.c video_filter/adjust_sat_hue.c video_filter/adjust_sat_hue.h
libadjust_plugin_la_LIBADD = $(LIBM)
libalphamask_plugin_la_SOURCES = video_filter/alphamask.c
@@ -75,6 +77,7 @@ video_filter_LTLIBRARIES = \
libcanvas_plugin.la \
libcolorthres_plugin.la \
libcroppadd_plugin.la \
+ libedgedetection_plugin.la \
liberase_plugin.la \
libextract_plugin.la \
libgradient_plugin.la \
diff --git a/modules/video_filter/edgedetection.c b/modules/video_filter/edgedetection.c
new file mode 100644
index 0000000..3693687
--- /dev/null
+++ b/modules/video_filter/edgedetection.c
@@ -0,0 +1,243 @@
+/******************************************************************************
+ * edgedetection.c : edge detection plugin for VLC
+ *****************************************************************************
+ * Copyright (C) 2016 VLC authors and VideoLAN
+ * $Id$
+ *
+ * Authors: Odd-Arild Kristensen <oddarildkristensen at gmail.com>
+ *
+ * This program 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.
+ *
+ * This program 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 this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
+ *****************************************************************************/
+
+/*****************************************************************************
+ * Preabmle
+ *****************************************************************************/
+#ifdef HAVE_CONFIG_H
+# include "config.h"
+#endif
+
+#include <vlc_common.h>
+#include <vlc_plugin.h>
+#include <vlc_filter.h>
+
+/*****************************************************************************
+ * Module descriptor
+ *****************************************************************************/
+#define EDGE_DETECTION_DESCRIPTION N_( "Edge detection video filter" )
+#define EDGE_DETECTION_TEXT N_( "Edge detection" )
+#define EDGE_DETECTION_LONGTEXT N_( \
+ "Detects edges in the frame and highlights them in white." )
+#define WHITE 255
+
+/*****************************************************************************
+ * Local prototypes
+ *****************************************************************************/
+static int Open( vlc_object_t * );
+static int Close( vlc_object_t * );
+static picture_t *new_frame( filter_t * );
+static picture_t *Filter( filter_t *, picture_t * );
+static uint8_t sobel( const uint8_t *, const int, const int, int, int);
+
+/* Kernel for X axis */
+static const signed char pi_kernel_x[3][3] = {
+ {-1, 0, 1},
+ {-2, 0, 2},
+ {-1, 0, 1}
+};
+
+/* Kernel for Y axis */
+static const signed char pi_kernel_y[3][3] = {
+ {-1, -2, -1},
+ {0, 0, 0},
+ {1, 2, 1}
+};
+
+vlc_module_begin ()
+
+ set_description( EDGE_DETECTION_DESCRIPTION )
+ set_shortname( EDGE_DETECTION_TEXT )
+ set_help( EDGE_DETECTION_LONGTEXT )
+ set_category( CAT_VIDEO )
+ set_subcategory( SUBCAT_VIDEO_VFILTER )
+ set_capability( "video filter2", 0 )
+ set_callbacks( Open, Close )
+
+vlc_module_end ()
+
+/* Store the filter chain */
+struct filter_sys_t
+{
+ filter_chain_t *p_chain;
+};
+
+/*****************************************************************************
+ * Opens the filter.
+ * Allocates and initializes data needed by the filter. The image needs to
+ * be black-and-white in order to detect any edges. The Gaussian blur is
+ * needed so that the Sobel operator does not give a high response for noise,
+ * or small changes in the image.
+ *****************************************************************************/
+static int Open( vlc_object_t *p_this )
+{
+ int i_ret;
+ es_format_t fmt;
+ filter_t *p_filter = (filter_t *)p_this;
+ filter_owner_t owner = {
+ .sys = p_filter,
+ .video = {
+ .buffer_new = new_frame,
+ },
+ };
+ /* Store the filter chain in p_sys */
+ p_filter->p_sys = (filter_sys_t *)filter_chain_NewVideo( p_filter, true, &owner );
+
+ if ( p_filter->p_sys == NULL)
+ {
+ msg_Err( p_filter, "Could not allocate filter chain" );
+ free( p_filter->p_sys );
+ return VLC_EGENERIC;
+ }
+ es_format_Copy( &fmt, &p_filter->fmt_in );
+ /* Clear filter chain */
+ filter_chain_Reset( (filter_chain_t *)p_filter->p_sys, &p_filter->fmt_in, &fmt);
+ /* Add adjust filter to turn frame black-and-white */
+ i_ret = filter_chain_AppendFromString( (filter_chain_t *)p_filter->p_sys,
+ "adjust{saturation=0}" );
+ if ( i_ret == -1 )
+ {
+ msg_Err( p_filter, "Could not append filter to filter chain" );
+ filter_chain_Delete( (filter_chain_t *)p_filter->p_sys );
+ return VLC_EGENERIC;
+ }
+ /* Add gaussian blur to the frame so to remove noise from the frame */
+ i_ret = filter_chain_AppendFromString( (filter_chain_t *)p_filter->p_sys,
+ "gaussianblur{deviation=1}" );
+ if ( i_ret == -1 )
+ {
+ msg_Err( p_filter, "Could not append filter to filter chain" );
+ filter_chain_Delete( (filter_chain_t *)p_filter->p_sys );
+ return VLC_EGENERIC;
+ }
+ /* Set callback function */
+ p_filter->pf_video_filter = Filter;
+ return VLC_SUCCESS;
+}
+
+/******************************************************************************
+ * Closes the filter and cleans up all dynamically allocated data.
+ ******************************************************************************/
+static int Close( vlc_object_t *p_this )
+{
+ filter_t *p_filter = (filter_t *)p_this;
+ filter_chain_Delete( (filter_chain_t *)p_filter->p_sys );
+ return VLC_SUCCESS;
+}
+
+/* *****************************************************************************
+ * Allocates a new buffer for the filter chain.
+ ******************************************************************************/
+static picture_t *new_frame( filter_t *p_filter)
+{
+ return filter_NewPicture( p_filter->owner.sys );
+}
+
+/******************************************************************************
+ * Callback function.
+ * This function implements the sobel operator which can be used to detect
+ * edges in a black-and-white image. The sobel operator is applied to
+ * every pixel in the frame for both X and Y axis.
+ ******************************************************************************/
+static picture_t *Filter( filter_t *p_filter, picture_t *p_pic )
+{
+ picture_t *p_filtered_frame =
+ filter_chain_VideoFilter( (filter_chain_t *)p_filter->p_sys, p_pic );
+ picture_t *p_out_frame = picture_NewFromFormat( &p_pic->format );
+ if ( p_out_frame == NULL )
+ {
+ picture_Release( p_filtered_frame );
+ msg_Err( p_filter, "Could not allocate memory for new frame" );
+ return NULL;
+ }
+ const int i_lines = p_filtered_frame->p[Y_PLANE].i_visible_lines;
+ const int i_pitch = p_filtered_frame->p[Y_PLANE].i_pitch;
+ /* Loop through every pixel in the frame */
+ for ( int i_line = 0; i_line < i_lines; i_line++ )
+ {
+ for ( int i_col = 0; i_col < i_pitch; i_col++ )
+ {
+ /* Set the new value for the pixel */
+ *( p_out_frame->p[Y_PLANE].p_pixels + ((i_pitch * i_line) + i_col) ) =
+ sobel( p_filtered_frame->p[Y_PLANE].p_pixels,
+ i_pitch, i_lines, i_col, i_line );
+ }
+ }
+ picture_Release( p_filtered_frame );
+ return p_out_frame;
+}
+
+/******************************************************************************
+ * Sobel Operator.
+ * Calculates the gradients for both X and Y directions in a frame.
+ ******************************************************************************/
+static uint8_t sobel( const uint8_t *p_pixels, const int i_pitch,
+ const int i_lines, int i_col, int i_line )
+{
+ int i_x_val = 0;
+ int i_y_val = 0;
+ int i_col_offset;
+ int i_line_offset;
+ for ( int i_x = 0; i_x < 3; i_x++ )
+ {
+ /* Check if we are at the first pixel on the scanline */
+ if (i_x == 0 && i_col == 0)
+ {
+ /* Duplicate the first pixel on the scanline */
+ i_col_offset = 0;
+ }
+ /* Check if we are on the last pixel on the scanline */
+ else if (i_x == 2 && i_col == i_pitch - 1)
+ {
+ /* Duplicate the last pixel on the scanline */
+ i_col_offset = i_pitch - 1;
+ }
+ else
+ {
+ i_col_offset = i_col + i_x - 1;
+ }
+ for ( int i_y = 0; i_y < 3; i_y++ )
+ {
+ /* Check if we are at the top scanline */
+ if (i_y == 0 && i_line == 0)
+ {
+ /* Duplicate the top pixel */
+ i_line_offset = 0;
+ }
+ /* Check if we are the bottom scanline */
+ else if (i_y == 2 && i_line == i_lines - 1 )
+ {
+ /* Duplicate the bottom pixel */
+ i_line_offset = i_pitch * (i_lines - 1);
+ }
+ else {
+ i_line_offset = i_pitch * (i_line + i_y - 1);
+ }
+ /* Apply the kernel to the pixel */
+ i_x_val += pi_kernel_x[i_x][i_y] * p_pixels[i_line_offset + i_col_offset];
+ i_y_val += pi_kernel_y[i_x][i_y] * p_pixels[i_line_offset + i_col_offset];
+ }
+ }
+ int i_ret = abs(i_x_val) + abs(i_y_val);
+ return (i_ret > WHITE) ? WHITE : i_ret;
+}
--
2.5.4 (Apple Git-61)
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