PBMPLUS, UTILITIES, Portable Bit Map Toolkit (10dec91 version) PBMPLUS is a toolkit for converting various image formats to and from portable formats, and therefore to and from each other. The idea is, if you want to convert among N image formats, you only need 2*N conversion filters, instead of the N^2 you would need if you wrote each one separately. In addition to the converters, the package includes some simple tools for manipulating the portable formats.