Are you really losing quality on PNGs? Or did you notice the quality loss on JPGs and assume it was a problem with your script? It's normal to lose quality on each save with JPG, because the format uses lossy compression, but that shouldn't happen with PNG.

$;=sub{$/};@;=map{my($a,$b)=($_,$;);$;=sub{$a.$b->()}}
split//,".rekcah lreP rehtona tsuJ";$\=$ ;->();print$/
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