(EN)
In a method and apparatus for analysing an electronic
image signal, the signal is treated as representing one or
more cells each comprising a plurality of pixels. A set of
pointers is generated and sequentially set according to
characteristic values related to detailed image content. The
pointers are used to address a memory array and for
successive frames, the values of an address in each array row
indicated by the pointer corresponding to that row is
updated. In this way, for each frame the characteristic
values can be accumulated so that in a single operational
mode, both a time history of the image, stored in a memory,
is updated and an indication is produced indicative of the
occurrence or non-occurrence of an event not associated with
image background. The characteristic values can be generated
by randomly or pseudo-randomly selecting pairs of pixels and
for each, generating a binary signal depending on whether or
not the intensity of incident light on a predetermined one of
the pair is greater than the intensity on the other. Over
all the rows, the values in the addresses being updated can
be summed, as well as the maximum value in each row. The
ratio of the two sums can be time weighted averaged with
respect to the ratios obtained from previous frames. The
ratio is compared with the average and the result used to
determine the occurrence or non-occurrence of a significant
event within the image.