We initiated a large project aimed to estimate the Luminosity Function of galaxies in clusters and to evaluate its relation to cluster morphology .
With this paper we deem necessary to outline the general procedures of the data reduction and details of the data analysis .
The cluster sample includes the brightest southern ROSAT all-sky survey clusters with z < 0.1 .
These have been observed in three colours g,~ { } r,~ { } i , and mapped up to a few core radii using a mosaic of CCD frames .
E/S0 galaxies in the cluster core are singled out both by morphology ( for the brightest galaxies ) , and by colour .
The details of the data reduction procedure are illustrated via the analysis of the cluster Abell 496 , which has been used as a pilot cluster for the whole program .
The related photometric catalogue consists of 2355 objects .
The limiting magnitudes ( the reference Surface Brightness is given in parenthesis ) in the various colours are respectively g ( 25.5 ) = 24.14 , r ( 25.5 ) = 24.46 , i ( 25.0 ) = 23.75 .
These correspond to the limiting absolute magnitudes -12.28 , -11.96 and -12.67 ( H _ { 0 } =50 km/sec/Mpc ) .