Huizinga, J.E. & van Albada, T.S. 1992, MNRAS 254, 677.
The surface photometry of Sc galaxies in the ESO-LV database in view of recent claims by Valentijn that spiral galaxies are opaque over their entire disks is analyzed. Using diameter-limited and magnitude-limited subsamples, it can discriminate between the opaque and transparent cases with the axis-ratio distribution test. Results support the traditional view that Sc galaxies are semitransparent, but the brightness difference between face-on and edge-on can be as large as 1.0 to 1.5 mag. Analyzing surface-brightness profiles at various radii, it is seen that the central regions are essentially opaque, and the outer regions nearly fully transparent. It is shown that conclusions differ from those of Valentijn, because of neglect to take secondary inclination effects into account.