TROUBLESHOOTING

Some issues encountered with Quack and how to solve them.

*** deepzoom does not work ***

There seems to be a problem with Perl 5.18+ and deepzoom 0.05.
http://search.cpan.org/~drrho/Graphics-DZI-0.05/script/deepzoom

It complains about an enum being wrongly initialized. 
https://metacpan.org/pod/release/ETHER/Moose-2.1106-TRIAL/lib/Moose/Manual/Delta.pod#pod2.1200

The problem can be solved by replacing
  enum 'packing' => qw( exponential linear );
with 
  enum 'packing' => [qw( exponential linear )];
in the file 
  /usr/local/share/perl/5.18.2/Graphics/DZI/A4.pm
(or similar folder). There will still be warnings with "given is 
experimental" and "when is experimental", but they are not critical
in Perl 5.18 (although this probably means that Graphics::DZI will
need further tweaks to work with later Perl versions).


*** The zoomable images are too bright ***

This issue has not been investigated fully. The text below is based on
speculation, but seems to produce the expected result.

It seems that conversion to PNG with newer versions of Graphics Magick
produces an image with Gamma (gAMA chunk) set to 1.0 if no gamma is
specified in the source image.

The common implicit assumption with no Gamma specified is Gamma 2.2
so the displayed tiles will appear very bright (1.0 -> 2.2).

To counter this effect, set Gamma explicitely to 0.4 (1.0 / 2.2) in the
QA image generation by adding the line

  export QA_EXTRA="+gamma 0.4"

to quack.settings. This specified the Gamma chunk without altering the
pixel values.