  We demonstrate a new multi-wavelength technique for two-dimensional
parametric modelling of galaxy surface-brightness profiles, which we have
incorporated into the widely used software GALFIT. Our new method, named
GALFITM, extends GALFIT3's current single-band fitting process by
simultaneously using multiple images of the same galaxy to constrain a
wavelength-dependent model. Each standard profile parameter may vary as a
function of wavelength, with a user-definable degree of smoothness, from
constant to fully free. The performance of GALFITM is evaluated by fitting
elliptical S\'ersic profiles to ugriz imaging data for 4026 galaxies,
comprising the original SDSS imaging for 163 low redshift (v < 7000 kms)
galaxies and 3863 artificially redshifted (0.01 < z < 0.25) images of the same
galaxies.
  Comparing results from single-band and multi-band techniques, we show that
GALFITM significantly improves the extraction of information, particularly from
bands with low signal-to-noise ratio (e.g., u and z SDSS bands) when combined
with higher signal-to-noise images. We also study systematic trends in the
recovered parameters, particularly S\'ersic index, that appear when one
performs measurements of the same galaxies at successively higher redshifts. We
argue that it is vital that studies investigating the evolution of galaxy
structure are careful to avoid or correct for these biases.
  The resulting multi-band photometric structural parameters for our sample of
163 galaxies are provided. We demonstrate the importance of considering
multi-band measurements by showing that the S\'ersic indices of spiral galaxies
increase to redder wavelengths, as expected for composite bulge-disk systems.
Finally, for the ellipticals in our sample, which should be well-represented by
single-S\'ersic models, we compare our measured parameters to those from
previous studies.
