The bzip2 choice is not set in stone. The reason why PNG is built on top of deflate is because back then there was nothing better around for the computing power

The bzip2 choice is not set in stone. The reason why PNG is built on top of deflate is because back then there was nothing better around for the computing power available. If you talk about speeds, the more or less only revelant measure is _decompression_ speed, and bzip2 is just fine for that. How long it takes to compress an image is relevant only once. Decompression is another story. Additionally, in pipelines, you would only decompress your image once and compress it once. Usually, when people build pipelines based on individual tools passing png's to each other, these steps are repeated n times for n elements of the pipeline.