spec       => {
     img_1 => {    
         gen_files => {       
             'img_1_thmb_1' => gen_thumb({ w => 100, h => 100 }),
             'img_1_thmb_2' => gen_thumb({ w => 50,  h => 50 }),
           }                                                                                                 
     },        
 },      

##</code><code>##

sub gen_thumb  {
  my %args = @_;
  return sub {
      my $self = shift;
      my $filename = shift;
      _really_gen_thumb($self, {
              filename => $filename,
              %args,
          });
  }
}

##</code><code>##

 spec => {
   img_1 => {   
     gen_files => {   
           'img_1_thmb_1' => {                                                                          
                   transform_method => \&gen_thumb,                
                   params => [{ w => 100, h => 100 }],                                                             
           }                                                                                                         
           'img_1_thmb_2' => {                                                                                      
                   transform_method => \&gen_thumb, 
                   params => [{ w => 50, h => 50 }], 
           }                                                                                                          
   }                                                                                                                
 },   
},