Using IO::String with a module

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

Hi, I have some code which directly captures images from a bt848 camera. It works OK. In the below code, the captured image is pnm, but it is in BGR format, so I need to reopen it with the Imager module, and use it's cool matrix method to convert it to RGB. Now my question is this: How can avoid writing the file twice to disk? First V4L writes a pnm, then I have to reopen the pnm with Imager.

I tried to change the output filehandle for the v4l pnm to a scalar string(I'm using 5.8), so instead of opening a file, I opened \$temp. That goes OK, but when I try to use Imager to open \$temp, it just dies and dumps \$temp to STDERR.

So is it possible to somehow pass \$temp to Imager?

#!/usr/bin/perl
use warnings;
use strict;
use Video::Capture::V4l;
use Imager;

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

   unless($count == 0){
      # save $fr now, as it contains the raw BGR data 
        open (JP,">z$count.pnm") or die $!;

        #my $temp=''; #this fails when passing to Imager
        # open (JP,">",\$temp)or die $!; 

        print JP "P6\n320 240\n255\n";  #header 
        print JP $nfr;
        close JP;

       # convert bgr to rgb 
       my $img = Imager->new();
       $img->open(file=>"z$count.pnm", type => 'pnm') or die $img->err
+str();
       my $newimg = $img->copy();
          $newimg = $img->convert(matrix=>[ [ 0, 0, 1 ],
                                            [ 0, 1, 0 ],
                                            [ 1, 0, 0 ] ]);
       $newimg->write(file=>"z$count.jpg", type=>'jpeg')
                          or die $img->errstr;

     }

 $count++;
 $frame = 1-$frame;
 $fr = $nfr;
}
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update (broquaint): added <readmore> tag

Comment on Using IO::String with a module Download Code

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Re: Using IO::String with a module by Zaxo (Archbishop) on Jul 06, 2003 at 15:57 UTC
From the Imager::Files pod, it appears that, `$img->read( data => $temp, type => 'pnm');` should work. You might consider just moving through the in-memory image with something like, `my $finger = 0; # or wherever the data starts while ($finger < length $temp) { substr( $temp, $finger, 3) = pack 'C3', reverse unpack 'C3', substr $temp, $finger, 3; $finger += 3; }` [download] Untested. Update: corrected code to assume 24-bit color. After Compline, Zaxo	[reply] [d/l] [select]
Re: Using IO::String with a module by zentara (Cardinal) on Jul 07, 2003 at 19:09 UTC
Thank You Zaxo, you answered 2 questions for the price of 1. :-) I was wondering how I could do the hex byte swap manually, with perl, and your pack-unpack method does work fine, but it is quite slow(plus Imager can convert to jpg). I played around some more, and found that I could save a little bit of processing by reversing the BGR string(which left it RGB but upside down and flipped :-)), then use Imager to do a hv flip. The advantge to this is I didn't need to make a copy of the imager object, since an hv flip can be done in-place on the object. The code I've settled on is below. use warnings; use strict; use Video::Capture::V4l; use Imager; my $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(0..1) { my $nfr = $grab->capture (1-$frame, 320, 240); $grab->sync($frame) or die "unable to sync"; unless($count == 0){ # save $fr now, as it contains the raw BGR data my $temp=''; open (JP,'>',\$temp) or die $!; print JP "P6\n320 240\n255\n"; #header $nfr = reverse $nfr; print JP $nfr; close JP; my $img = Imager->new(); $img->read(data=>$temp,type =>'pnm') or warn $img->errstr(); $img->flip(dir=>"hv"); $img->write(file=>"z$count.jpg", type=>'jpeg') or warn $img->errstr; } $count++; $frame = 1-$frame; $fr = $nfr; } [download]	[reply] [d/l]