Phytec eGrabber-4plus, Hardware Manual

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eGrabber-4plus
84 
PHYTEC Meßtechnik GmbH 2004 L-608e_4
If continuous digitalization is desired, then image information is
written to the memory space of the even image during the subsequent
20 ms.
It is important to note here that in this time frame the old image
information in this memory space will be continually replaced by new
information. This can lead to false interpretations of the image
contents by the software, especially in scenes that have been moved.
Now we consider the case of digitizing a whole frame in one memory
region. Here the same effect might occur but in some different
fashion. After 20 msec digitization the information for an odd field is
completely available and therefore all odd lines are defined, but the
even lines are not defined. During the following 20 msec the data for
the even field are received. Therefore there is no time, which is not
used to transfer data to the memory except for the blanking interval.
So there is always a point (X,Y) where old and new information are
stored adjacently, so that a mismatch will show up.