An image resource, returned by one of the image creation functions, such as imagecreatetruecolor().
The path to save the file to. If not set or
NULL, the raw image stream
will be outputted directly.
NULL is invalid if the quality and
filters arguments are not used.
Compression level: from 0 (no compression) to 9.
Allows reducing the PNG file size. It is a bitmask field which may be
set to any combination of the
PNG_ALL_FILTERS may also be used to respectively
disable or activate all filters.