Learning About PNG


There is no uncompressed variant of PNG. It is possible to store uncompressed 
data by using only uncompressed deflate blocks (a feature normally used to 
guarantee that deflate does not make incompressible data much larger). 
However, PNG software must support full deflate/inflate; any software that 
does not is not compliant with the PNG standard. The two most important 
features of PNG---portability and compression---are absolute requirements 
for online applications, and users demand them. Failure to support full 
deflate/inflate compromises both of these objectives.