my $nr = $1 if $hires =~ m{(\d+)\.\w+$} || warn "can't find number in $hires";
next unless $nr;
my $file = slide_jpg( $factor => $nr );
+ next if -e $file;
warn "slide $hires -> $file\n";
-# next if -e $file;
my $im = Graphics::Magick->new;
$im->ReadImage( $hires );