There have been many utilities written over time to convert graphics to the charset and BGMap formats used on the Virtual Boy. However, they are either poorly documented and hard to use or they have little or no support for BGMaps, forcing programmers to use inefficient ways of storing graphics, like having a separate charset for each BGMap.
This program, however, can take multiple BMP files at once and convert them to BGMaps that all share the same charset, with the charset only containing as many characters as needed to conserve space and the BGMaps only containing as many tiles as needed, not all 64 by 64.