Studio delle prestazioni di un sistema a fosfori per mammografia ...

where £ is the system gain.
The PSF has a functional form identical to that of the image generated by a Æ-pulse input. If
the system is space invariant, a point-source input can be moved along the object plane without
any effect other than changing the location of its image, the function being the same for any
point Ü� Ý . So the dependence of the PSF on space variables can only be related to Ü� Ý as
far as the location of its center is concerned. The value of the PSF on the image plane merely
depends on the displacement at that location from the particular image point at which the PSF
is centered (see Fig. 2.1).
Figure 2.1: Convolution of a source composed of Æ functions with the PSF. The resulting pattern
is the sum of all the spread out contributions.
In other words it can be stated that:
ÈË� Ü� Ý� �� � �ÈË� � Ü� � Ý (2.5)
then, under the hypotheses of space invariance and linearity,
� �� � �£
��
� Ü� Ý ÈË� � Ü� � Ý �Ü�Ý (2.6)
It is also worth defining the Line Spread Function (LSF) as the integral of the PSF along
one direction, since this is the quantity that will be used to experimentally evaluate the spatial
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