  We investigate the effect of the "high-pass filter" data reduction technique
on the Herschel PACS PSF and noise of the PACS maps at the 70, 100 and 160 um
bands and in medium and fast scan speeds. This branch of the PACS Photometer
pipeline is the most used for cosmological observations and for point-source
observations.The calibration of the flux loss due to the median removal applied
by the PACS pipeline (high-pass filter) is done via dedicated simulations
obtained by "polluting" real PACS timelines with fake sources at different flux
levels. The effect of the data reduction parameter settings on the final map
noise is done by using selected observations of blank fields with high data
redundancy. We show that the running median removal can cause significant flux
losses at any flux level. We analyse the advantages and disadvantages of
several masking strategies and suggest that a mask based on putting circular
patches on prior positions is the best solution to reduce the amount of flux
loss. We provide a calibration of the point-source flux loss for several
masking strategies in a large range of data reduction parameters, and as a
function of the source flux. We also show that, for stacking analysis, the
impact of the high-pass filtering effect is to reduce significantly the
clustering effect. The analysis of the global noise and noise components of the
PACS maps shows that the dominant parameter in determining the final noise is
the high-pass filter width. We also provide simple fitting functions to build
the error map from the coverage map and to estimate the cross-correlation
correction factor in a representative portion of the data reduction parameter
space.
