  We present corrections for the change in the apparent scalelengths, central
surface brightnesses and axis ratios due to the presence of dust in pure disk
galaxies, as a function of inclination, central face-on opacity in the B-band
(tau^f_B) and wavelength. The correction factors were derived from simulated
images of disk galaxies created using geometries for stars and dust which can
reproduce the entire spectral energy distribution from the ultraviolet (UV) to
the Far-infrared (FIR)/submillimeter (submm) and can also account for the
observed surface-brightness distributions in both the optical/Near-infrared and
FIR/submm. We found that dust can significantly affect both the scalelength and
central surface brightness, inducing variations in the apparent to intrinsic
quantities of up to 50 percent in scalelength and up to 1.5 magnitudes in
central surface brightness. We also identified some astrophysical effects for
which, although the absolute effect of dust is non-negligible, the predicted
variation over a likely range in opacity is relatively small, such that an
exact knowledge of opacity is not needed. Thus, for a galaxy at a typical
inclination of 37 degrees and having any tau^f_B>2, the effect of dust is to
increase the scalelength in B relative to that in I by a factor of 1.12 +- 0.02
and to change the B-I central colour by 0.36 +- 0.05 magnitudes. Finally we use
the model to analyse the observed scalelength ratios between B and I for a
sample of disk-dominated spiral galaxies, finding that the tendency for
apparent scalelength to increase with decreasing wavelength is primarily due to
the effects of dust.
