  Recent surveys monitoring millions of light curves of resolved stars in the
LMC have discovered several microlensing events. Unresolved stars could however
significantly contribute to the microlensing rate towards the LMC. Monitoring
pixels, as opposed to individual stars, should be able to detect stellar
variability as a variation of the pixel flux. We present a first application of
this new type of analysis (Pixel Method) to the LMC Bar. We describe the
complete procedure applied to the EROS 91-92 data (one tenth of the existing
CCD data set) in order to monitor pixel fluxes. First, geometric and
photometric alignments are applied to each images. Averaging the images of each
night reduces significantly the noise level. Second, one light curve for each
of the 2.1 10^6 pixels is built and pixels are lumped into 3.6"x3.6"
super-pixels, one for each elementary pixel. An empirical correction is then
applied to account for seeing variations. We find that the final super-pixel
light curves fluctuate at a level of 1.8% of the flux in blue and 1.3% in red.
We show that this noise level corresponds to about twice the expected photon
noise and confirms previous assumptions used for the estimation of the
contribution of unresolved stars. We also demonstrate our ability to correct
very efficiently for seeing variations affecting each pixel flux. The technical
results emphasised here show the efficacy of the Pixel Method and allow us to
study luminosity variations due to possible microlensing events and variable
stars in two companion papers.
