  Data reduction procedures are aimed to minimize the impact of data
acquisition imperfections on the measurement of data properties with a
scientific meaning for the astronomer. To achieve this purpose, appropriate
arithmetic manipulations with data and calibration frames must be performed.
Furthermore, a full understanding of all the possible measurements relies on a
solid constraint of their associated errors. We discuss different strategies
for obtaining realistic determinations of final random errors. In particular,
we highlight the benefits of considering the data reduction process as the full
characterization of the raw-data frames, but avoiding, as far as possible, the
arithmetic manipulation of that data until the final measure and analysis of
the image properties. This philosophy will be used in the pipeline data
reduction for ELMER and EMIR.
