Video signal analysis

Abstract

In order to detect interlace errors in a video signal, one receives successive digitally coded frames, each frame comprising data for a field of a first type and data for a field of a second type (i.e. a top field and bottom field or vice versa). One then generates for each field of the first type:—a first difference signal (D1 F1) representative of the difference between the field and the second-type field of the previous frame;—a second difference signal (D1 F2) representative of the difference between the field and the second-type field of the same frame; and—a third difference signal (D1 F3) representative of the difference between the field and the second-type field of the following frame. Then, in dependence of the values of said difference signals, a decision signal (wOFlag) is generated indicating an estimated temporal relationship of the field to the second-type field of the same frame. This can be compared with a signal (IDFO) indicating a purported temporal relationship, and an alarm signal (wEFlag) generated in the event of a mismatch.

Dependencies are inferred from the claim text.