Editing PNG (section)

==== DEFLATE optimization ====
[[Zopfli]] and the [[7zip#Software development kit|LZMA SDK]] provide [[DEFLATE]] implementations that can produce higher [[Data compression ratio|compression ratio]]s than the [[zlib]] reference implementation at the cost of performance. AdvanceCOMP's <code>advpng</code> and <code>advdef</code> can use either of these libraries to re-compress PNG files. Additionally, [[PNGOUT]] contains its own [[proprietary software|proprietary]] DEFLATE implementation.

<code>advpng</code> doesn't have an option to apply filters and always uses filter 0 globally (leaving the image data unfiltered); therefore it should not be used where the image benefits significantly from filtering. By contrast, <code>advdef</code> from the same package doesn't deal with PNG structure and acts only as a re-deflater, retaining any existing filter settings.