  The objective of this work is to obtain an extinction-corrected distribution
of optical surface brightness and colour indices of the large nearby galaxy M
31 using homogeneous observational data and a model for intrinsic extinction.
  We process the Sloan Digital Sky Survey (SDSS) images in ugriz passbands and
construct corresponding mosaic images, taking special care of subtracting the
varying sky background. We apply the galactic model developed in Tempel et al.
(2010) and far-infrared imaging to correct the photometry for intrinsic dust
effects.
  We obtain observed and dust-corrected distributions of the surface brightness
of M 31 and a map of line-of-sight extinctions inside the galaxy. Our
extinction model suggests that either M 31 is intrinsically non-symmetric along
the minor axis or the dust properties differ from those of the Milky Way.
Assuming the latter case, we present the surface brightness distributions and
integral photometry for the Sloan filters as well as the standard UBVRI system.
We find the following intrinsic integral colour indices for M 31: (U-B)_0=0.35;
(B-V)_0=0.86; (V-R)_0=0.63; (R-I)_0=0.53; the total intrinsic
absorption-corrected luminosities of M 31 in the B and the V filters are 4.10
and 3.24 mag, respectively.
