Thank you vr! The module works as expected when following your instructions. Apparently the documentation synopsis contains two severe errors.

Imager::GIF synopsis:

my $sonic = Imager::GIF->new(file => 'sonic.gif');

Should be:

my $sonic = Imager::GIF->read(file => 'sonic.gif');

Imager::GIF synopsis:

$small_sonic->write(file => 'small_sonic.gif');

Should be:

$small_sonic->write('small_sonic.gif');

The first problem, not using the read method to construct the object, was causing the write error. The second issue, supplying a hash instead of file name to write method, silently fails to do anything.

Kudos