note 115534 deleted from function.imagepng by salathe

Note Submitter: htmlstudio ---- Quality at level 0 can be smaller than 9 (checked in php 5.4), reason is that 1-9 is "zlib compression", but 0 represent "Huffman compression" ("not compression" is a lie). Try both levels and choose better one. Using some external program (like optipng) is also good idea. Imagick extension have also several methods, which you can use to optimize image. You can read more about png compression at http://www.imagemagick.org/Usage/formats/#png_quality