russellp has asked for the wisdom of the Perl Monks concerning the following question:

Hi All.

I've looked around quite a bit and can't find a Perl Module that works with Webcam's. So I have decided to write one using OpenCV2.0 and Im having a problem.

My module: 

package OpenCV::Webcam;

our %EXPORT_TAGS = ( 'all' => [ qw(
    
) ] );

our @EXPORT_OK = ( @{ $EXPORT_TAGS{'all'} } );

our @EXPORT = qw(
    
);

our $VERSION = '0.01';


use Inline C => Config => 
               MYEXTLIB => 'C:\OpenCV2.0\lib\libcv200.dll.a  C:\OpenCV
+2.0\lib\libhighgui200.dll.a C:\OpenCV2.0\lib\libcxcore200.dll.a',
           INC      => '-IC:\OpenCV2.0\include\opencv';

use Inline C => <<'END_OF_C_CODE';


#include "cv.h"
#include "highgui.h"

CvCapture *capture = 0;
IplImage  *frame = 0;

int* height, width, step, channels, depth;


int new() {

capture = cvCaptureFromCAM( 0 );

printf("\nSetting Capture!\n");


}

char* GetImage() {

char *data;

printf("\nGetting Image Data!\n");

frame = cvQueryFrame( capture );

cvCvtColor(frame, frame, CV_BGR2RGB); 

data      = (char*)frame->imageData;
return(data);

}


int Release() {

printf("\nReleasing Capture!\n");
cvReleaseCapture( &capture );

}


END_OF_C_CODE

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The problem Im having is in the function GetImage() I return the binary image data back to Perl, their I use Gtk2 to provide a window to display the image. 

use Gtk2 '-init';
use Glib qw(TRUE FALSE);

use OpenCV::Webcam ;


$window = Gtk2::Window->new();


$capture = OpenCV::Webcam::new();

$data = OpenCV::Webcam::GetImage();

$pixbuf = Gtk2::Gdk::Pixbuf->new_from_data ($data, 'rgb', FASLE, 8, 64
+0, 480, 1920);
$image = Gtk2::Image->new_from_pixbuf ($pixbuf);


$window->add($image);

$window->show_all();

Gtk2->main;

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The error I get is - 

GLib-GObject-CRITICAL **: g_param_spec_float: assertion `default_value
+ >= minimum && default_value <= maximum' failed at web.pl line 8.

Gtk-CRITICAL **: gtk_widget_class_install_style_property: assertion `G
+_IS_PARAM_SPEC (pspec)' failed at web.pl line 8.

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But sometimes I get an image, But most of the time I get the runtime error.

Im using Perl5.0008 And Gtk2 from lost mind

My question is this: Is the IplImage *frame->imageData from C compatible with Perl? And should it be suitable for Gtk2::Gdk::Pixbuf->new_from_data?

Any help on this is greatly appreciated for it will be FREE software when Im done!

-Thanks,

Replies are listed 'Best First'.
Re: Open CV problem
by Tux (Canon) on Dec 09, 2010 at 15:42 UTC

    Will this also work on non-Windows? Your code is very Windows oriënted.

    Most character or data pointers in C cannot be used just as such in perl. They will have to be converted to a SCALAR value, in case of a string this will be a PV.

    You will have to read the Inline::C man-page and the perlguts manpage. Good luck!


    Enjoy, Have FUN! H.Merijn
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      Most character or data pointers in C cannot be used just as such in perl. They will have to be converted to a SCALAR value

      The nice thing about Inline::C is that it should take care of this, i.e. the necessary .xs (and .c) code doing the conversions is created behind the scenes - at least for simple types such as char*.

      For example, the following function returning a char* is mapped to a normal scalar on the Perl side: 

      #!/usr/bin/perl

use Inline C => Config => BUILD_NOISY => 1, CLEAN_AFTER_BUILD => 0;
use Inline C => <<'END_OF_C_CODE';

char* GetImage() {

    char *data = "test-test-test";

    return(data);
}
END_OF_C_CODE


my $data = GetImage();

print "$data\n";    # "test-test-test"

      [download]

      (btw, the CLEAN_AFTER_BUILD => 0 option I've specified above is very useful when you want to look at the auto-generated XS/C wrapper code for debugging purposes)

      So, if the data as returned by the OP's GetImage() function is in fact char*, things should just work fine in this regard. In other words, I suspect the problem lies elsewhere...

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        When I do a printf(data); in C, I get the same out put from Perl when I do print("$data\n"); Sample out put is below.

        Read more... (3 kB)

        This look like binray data to me. But not sure if Gtk2::Pixfuf new_from_data can use this directly. I.E is their a header it looks for or somthing..... Not sure.

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