Compress::Zlib is required to write compressed text.
Existing text tags are always rewritten in their original form (compressed
zTXt, uncompressed tEXt or internation iTXt), so pre-existing compressed
information can only be modified if Compress::Zlib is available.
Newly created textual information is written in uncompressed tEXt form by
default, or as compressed zTXt if the Compress option is used and
Compress::Zlib is available (but only if the resulting compressed data is
smaller than the original text, which isnt always the case for short text