  We present a method to obtain quantitative measures of galaxy morphology and
apply it to a spectroscopic sample of field galaxies in order to determine the
luminosity and stellar mass functions of galactic disks and spheroids. We
estimate, for each galaxy, the bulge-to-disk luminosity ratio in the I-band
using a two-dimensional image fitting procedure. Monte Carlo simulations
indicate that reliable determinations are only possible for galaxies
approximately two magnitudes brighter than the photometric completeness limit,
leaving a sample of 90 galaxies with well determined bulge-to-total light
ratios. We construct the luminosity functions of disks and spheroids and, using
a stellar population synthesis model, we estimate the stellar mass functions of
each of these components. The disk and spheroid luminosity functions are
remarkably similar. We do, however, find evidence in the bi-variate luminosity
function that spheroid-dominated galaxies occur only among the brightest
spheroids, while disk-dominated galaxies span a much wider range of disk
luminosities. Remarkably, the total stellar mass residing in disks and
spheroids is approximately the same. For our sample, we find the ratio of
stellar masses in disks and spheroids to be 1.3+/-0.2. Ongoing large
photometric and redshift surveys will lead to a large increase in the number of
galaxies to which our techniques can be applied and thus to an improvement in
the current estimates. (abridged)
