[vlc-devel] [PATCH] Implemented a new edge detection video filter
Jean-Baptiste Kempf
jb at videolan.org
Fri Feb 5 16:33:48 CET 2016
This was merged, thanks.
I had to update NEWS, POTFILES.in, MODULES_LIST and fix a typo, though.
On 04 Feb, Odd-Arild Kristensen wrote :
> 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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--
With my kindest regards,
--
Jean-Baptiste Kempf
http://www.jbkempf.com/ - +33 672 704 734
Sent from my Electronic Device
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