This works for me: 
#!/usr/bin/perl
use warnings;
use strict;
use Imager;

my $file = shift;
my $img = Imager->new();
$img->open(file=>$file) or die $img->errstr();

my $newimg = $img->convert(preset=>'grey');
$newimg->write(file=>'gray.jpg');

[download]

In reply to Re: converting Jpeg to grayscale by zentara
in thread converting Jpeg to grayscale by Anonymous Monk

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