Michio Ono has uploaded Micono RbPNGLib plugin at:

Micono RbPNGLib is a plugin for REALbasic ver.3.5 or later, provides some
abilities to handle PNG for Rb. To make this available, you should locate
this plugin in the Plugins folder of Rb and lauch Rb. RbPNGLib enables you
to read/write the PNG main image,its alpha channnel,its internal texts and