Music pages can be JPGs, PNGs, GIFs or any other graphic file format that Java and JAI supports by default. It is also possible to read PDF files directly, or ConvertFromPdf to graphic file formats that are usable by VirtMus.
The resolution of the images should be approximately the same as the resolution of the display. If it is much higher, the application will consume too much memory trying to work with them. If it is much lower they will not look sharp when stretched to fill the whole display.
Color depth can also make a huge difference. For example, VirtMus will handle 8-bit grayscale jpegs much faster than a 32-bit png file and for sheet music which is primarily black and white the difference between the two formats is probably not noticeable. The annotations can still be drawn in color even if the source music file is grayscale.
ImageMagic is a useful tool to convert graphics files between every imaginable format. Download the latest binary release for your platform from http://www.imagemagick.org/script/binary-releases.php
To convert your music page images to 8-bit grayscale jpegs, you can use the
convert program which is part of
ImageMagic with the following command line
convert -colorspace Gray -depth 8 SomeMusicFile.??? SomeMusicFile-converted.jpg