# get all the samples for row $y
my @samples = $image->getsamples(y => $y, channels => [ 0 ]);
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my @samples = $image->getsamples(y => $y);
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my $samples = $image->getsamples(y => $y);
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Yes, this is looking more promising. The triplet values were not as useful as hoped for. I tried to use the getsamples() method to sample just one pixel, however, and the results were like:

«ÑçÇ¡yÀʾ²¾í©k~Áµ¨rw
U=9dyµàТI*\ZGpë«
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I'm not sure how to compare those values to each other... My code to do this was as follows:

###
#it appears there may actually be a way to read the grey channel
#using the "getsamples" routine
my $ycoord = 5;
my $xcoord = 5;
my $sample = $img->getsamples(y => $ycoord, x => $xcoord);
print "we sampled 5,5 to have a value of $sample\n";
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I tried sampling two different points that I knew to be quite different by this method, which is how I got those two odd strings above. I'll have to look further into the Perldocs for Imager, it appears :)

You're running into 2 problems here:
• getsamples() uses the context you call it in to decide whether to produce samples packed into a string or a list of samples
• if you don't supply a width getsamples() returns samples from the given x position all the way to the right side of the image.
So to get just the sample for one pixel as an integer you'd do:

my ($sample) = $image->getsamples(x => $x, y => $y, width => 1);
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But if you're looking for speed you'll probably find that working a row at a time is faster:

for my $y ( 0 .. $image->getheight() - 1 ) {
  for my $sample ($image->getsamples(y => $y)) {
    # do something with the sample
  }
}
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If you have the RGB-values you can easily convert them to grayscale through the formula on Wikipedia where Y (luminance) is the grayscale intensity:

Y = 0.299 * R + 0.587 * G + 0.114 * B

Here is the link:
http://en.wikipedia.org/wiki/YUV

Anders, Norway

I may be wrong, but I would expect any of the modules mentioned to return just an intensity in the case of a true grayscale image, I could be wrong, or it could be a case of the image technically being a color image that just so happens to only contain grays. Nonetheless, if all else fails, just use any one of the values, ignore the others, they should be the same.

Well, just did some testing, and at least in regards to Image::Magick it still returns RGBA values, I can't speak for the others haven't had much experience with them, so at least in the case of Image::Magick, I would suggest just dumping the spare values.

<#!/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');
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