The above is an integrated spectrum of the galaxy NGC 3512. The relavant data is from 3500 - 6000 angstroms. Since the galaxy light is a collection of the light from individual stars, it should be possible to combine the spectra on the previous page in either a linear or non-linear way to approximately reproduce a galaxy spectra. This is difficult, though, so don't expect to succeed. However, a simple linear combination of just a few stellar types should approximately give the right spectral energy distribution (the overall shape of the spectrum) as well as some of the prominent features (\eg stellar absorption lines).
Click Here for the actual data that comprises the the figure above
Watch this space for the JAVA spectral combination utility