Legacy ImageMagick Discussions Archive

I've got a Centos-5.3 box (based on a vmlinuz-2.6.18-128.1.10.el5 kernel), and trying to run some Perl code I had running on a different box.

My code does essentially:
$commandstring = sprintf("compare -metric PSNR /home/Movies/FD%04i.jpg /home/Movies/FD%04i.jpg null:",$counter,$counter-1);
print $commandstring . "\n";
$DiffString = `$commandstring`;
print "/" . $DiffString . "/\n";
($DiffNum) = $DiffString =~ /(\d+(?:\.\d+)?)/;
print "[" . $DiffNum . "]";

With the latest release (v6.5.6-9) on the new box, $DiffString was <BLANK>, so I never pulled a number out of it.

When I found the rpms for 6.2.8-4, which was running on the old box just fine, and downgraded to that, my code started working again.

I can see the SNR number when I run the command from the command line, and I'd be happy to have just that, but the SNR number doesn't make it into $DiffString.

Is there something special you have to do to ensure the backtick operator picks up the output of convert? Did something change between 6.2.8-4 and 6.5.6-9?

Am I missing details which might help solve this problem?

Thanks!

Try redirecting standard error to standard out (.e.g >/dev/null 2>&1).

Yup, that worked, at least when I did:

$commandstring = sprintf("compare -metric PSNR /home/Movies/FD%04i.jpg /home/Movies/FD%04i.jpg null: 2>&1",$counter,$counter-1);

is this a bug, will it get fixed, or is the output supposed to goto stderr?

Thanks for the quick response!

The output is supposed to go to standard error to permit an image to standard out:

• compare -metric rmse image.png reference.png -