Extragalactic database. VI. Inclination corrections for spiral galaxies and disk opaqueness in the B-band.

We have investigated the inclination corrections to be made on the B-band photometric parameters for spiral galaxies (2<=T<=7). A model, with a single free parameter C, provides the determination of inclination corrections on diameter, magnitude and mean surface brightness. This coefficient C, which gives the diameter inclination correction in the linear approximation, is numerically derived from a statistical analysis, using the Tully-Fisher relation for diameters, together with kinematical distances. Special care is taken to avoid biases. The validity of the model is verified by consistency tests on magnitudes and surface brightness. As a by-product, this study provides information about the controversial question of the opaqueness of the edges of galactic disks in blue magnitude. We conclude that, on the mean, galaxy disks have a relatively high opaqueness τ=~1.00 at the surface brightness of 25mag/arcsec^2^