If I were to guess I think you should try
quality => 50. If I remember right, I would guess that quality is the percentage of the original image - so a value of 80 would mean compress to 80% of the quality of the uncompressed version. That would mean that specifying a quality of 100 is leaving compression off entirely -- which is the same as the original -- which is the same as
compression => 'None'.
my @a=qw(random brilliant braindead); print $a[rand(@a)];