This Readme says that Imager uses libpng. The libpng Manual says that it offers several functions to control the compression options, named png_set_compression_*, the central one being png_set_compression_level. The Imager source does not seem to call these functions at all. So unfortunately the answer to your question seems to be no, there is currently no way to set the compression level. You may want to file a wishlist item in the issue tracker, or perhaps even hack the source yourself.

In reply to Re: Setting png compression level in Imager by haukex
in thread Setting png compression level in Imager by Anonymous Monk

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