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Imager Cookbook

Details

Imager::Cookbook contains recipes for working with Imager.
FILES
This is described in detail in Imager::Files.
Reading an image from a file
my $image = Imager->new;
$image->read(file=>$filename) or die $image->errstr;
See Imager::Files.
Writing an image to a file
$image->write(file=>$filename) or die $image->errstr;
Write an animated gif.
build an array of images to use in the gif
my @images;
synthesize the images or read them from files, it doesn't matter
...
write the gif
Imager->write_multi({ file=>$filename, type=>'gif' }, @images)
or die Imager->errstr;
See "Writing an animated GIF" in Imager::Files for a more detailed example.
Reading multiple images from one file
Some formats, like GIF and TIFF support multiple images per file. Use the read_multi() method to read them:
my @images = Imager->read_multi(file=>$filename)
or die Imager->errstr;
Converting from one file format to another
This is as simple as reading the original file and writing the new file, for single images:
my $image = Imager->new;
Imager auto-detects the input file type
$image->read(file => $input_filename)
or die $image->errstr;
Imager derives the output file format from the filename
$image->write(file => $output_filename)
or die $image->errstr;
or you can supply a type parameter:
$image->write(file => $output_filename, type => 'gif')
or die $image->errstr;
The main issue that can occur with this is if the input file has transparency and the output file format doesn't support that. This can be a problem when converting from GIFs to JPEGs for example.
To work around that you can compose the source image onto a background color:
if ($image->getchannels == 4 or $image->getchannels == 2) {
my $back = Imager->new(xsize => $image->getwidth,
ysize => $image->getheight);
grey background for grayscale images, red for color
my $back_color = $image->getchannels == 2 ? [ 128 ] : 'red';
$back->box(filled => 1, color => $back_color);
$back->rubthrough(src => $image);
$image = $back;
}
now we can write safely to jpeg or pnm
Some formats support multiple files, so if you want to convert from say tiff to jpeg, you'll need multiple output files:
my @images = Imager->read_multi(file => 'input.tif')
or die Imager->errstr;
my $index = 1;
for my $image (@images) {
$image->write(file => sprintf('output%02d.jpg', $index++))
or die $image->errstr;
}
Requirements:
· Perl

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