in reply to capturing raw video with v4l

Here's a way to use Image::Magick to create PNGs from the raw RGB data.

Untested code:

#!/usr/bin/perl

die "Usage: $0 image1 .. imageN\nDo not include the .raw extension.\n"
+ unless (@ARGV);

use Image::Magick;

my $depth = 8; # or 16 or 24 or ...
my $size = '640x480';

foreach my $file (@ARGV) {
  my $image = Image::Magick->new;
  my $x;
  $x = $image->Read(
    filename => "rgb:$file.raw",
    size => '640x480',
    depth => $depth
  );
  warn "$x" if "$x"; # from the examples but looks funny to me ;-)
  $x = $image->Write("$file.png"); # or jpg or whatever
  warn "$x" if "$x";
}

[download]

Alternately, you could include this in your video capture script. That would enable you to save a step by converting the raw data stored in the $nfr scalar to PNG.

Replies are listed 'Best First'.
Re: Re: capturing raw video with v4l
by zentara (Cardinal) on Jul 04, 2003 at 21:00 UTC
    Well thanks, you got me on the right track. As usual, I make advances by making "educated guesses". :-) I noticed that the output of videodog's raw frame, and a pnm frame was the same except for a header. So I added a header to each frame and renamed it pnm. Now another problem arises....the raw data is actually BGR not RGB ( I thought it was a typo, but it's not). So now I need to figure out how to quickly process the frame to change it from BGR to RGB.

    New code which outputs blue-tinted pnm's. 

    #!/usr/bin/perl

use Video::Capture::V4l;

$grab = new Video::Capture::V4l
   or die "Unable to open Videodevice: $!";

$|=1;
my $frame=0;
my $fr=$grab->capture ($frame, 320, 240);

my $count=0;
for(1..5) {
   my $nfr = $grab->capture (1-$frame, 320, 240);
   $grab->sync($frame) or die "unable to sync";

   # save $fr now, as it contains the raw BGR data 
   open (JP,">z$count.pnm") or die $!;
   print JP "P6\n320 240\n255\n";  #header 
   print JP $nfr;
   close JP;
   print ".";
   $count++;
   $frame = 1-$frame;
   $fr = $nfr;
}

    [download]
[reply]
[d/l]
      Don't know how quick it is, but here's my stab at converting from BGR to RGB. 
      sub convert_to_rgb {
  my $bgr = shift;
  my $bgrLen = length($bgr);
    
  #Unpacking the BGR data gives use easy access to individual bytes.
  my @bgrArray = unpack("C$bgrLen",$bgr);
  my @rgbArray;
    
  my $ct=0;
  while ($ct < $bgrLen) {
    $rgbArray[$ct] = $bgrArray[$ct+2];
    $rgbArray[$ct+1] = $bgrArray[$ct+1];
    $rgbArray[$ct+2] = $bgrArray[$ct];
    $ct+=3;
  }

  #Pack the data to match the input format.
  my $rgb = pack("C$bgrLen",@rgbArray);
   
  return $rgb;
}

      [download]
      Pass the code $nfr and the returned value can be written to file in place of $nfr.
[reply]
[d/l]
        Hi, that's a nice pure perl snippet, however it still would be faster to let Imager do it, since it uses xs and C to do the same thing, and faster too for big image files.
        I'm not really a human, but I play one on earth. flash japh
[reply]

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