PNG uses a 2-stage compression process:
pre-compression: filtering (prediction)
compression: DEFLATE
PNG uses DEFLATE, a non-patented lossless data compression algorithm involving a combination of LZ77 and Huffman coding.
Permissively-licensed DEFLATE implementations, such as zlib, are widely available.

Compared to formats with lossy compression such as JPG, choosing a compression setting higher than average delays processing, but often does not result in a significantly smaller file size.
PNG uses a 2-stage compression process:
pre-compression: filtering (prediction)
compression: DEFLATE
PNG uses DEFLATE, a non-patented lossless data compression algorithm involving a combination of LZ77 and Huffman coding. Permissively-licensed DEFLATE implementations, such as zlib, are widely available.
Compared to formats with lossy compression such as JPG, choosing a compression setting higher than average delays processing, but often does not result in a significantly smaller file size.
Portable Network Graphics