Thanks for your quick reply.
For quality - I was trying to do it as it's mentioned in docs http://www.imagemagick.org/Usage/formats/#png . Did I get it wrong?
For quality - I was trying to do it as it's mentioned in docs http://www.imagemagick.org/Usage/formats/#png . Did I get it wrong?
PNG compression
When used with PNG output, quality is regarded as two decimal figures. The first digit (tens) is the zlib compression level, 1-9. However if a setting of '0' is used you will get Huffman compression rather than 'zlib' compression, which is often better! Weird but true!
The second digit is the PNG data encoding filtering (before it is comressed) type: 0 is none, 1 is "sub", 2 is "up", 3 is "average", 4 is "Paeth", and 5 is "adaptive". So for images with solid sequences of color a "none" filter (-quality 00) is typically better. For images of natural landscapes an "adaptive" filtering (-quality 05) is generally better.