Description:

This pure Ruby library can read and write PNG images without depending
on an external image library, like RMagick. It tries to be memory
efficient and reasonably fast.

It supports reading and writing all PNG variants that are defined in
the specification, with one limitation: only 8-bit color depth is
supported. It supports all transparency, interlacing and filtering
options the PNG specifications allows. It can also read and write
textual metadata from PNG files. Low-level read/write access to PNG
chunks is also possible. This library supports simple drawing on the
image canvas and simple operations like alpha composition and
cropping. Finally, it can import from and export to RMagick for
interoperability.