Device for following and estimating the local state of picture contours

For use in a differential coded pulse modulation coder or decoder a device for following and recursively estimating the local state of picture contours defined by lines of N points, N being an integer, said points being distributed in accordance with an orthogonal sampling structure, each line beginning with a line start signal DL and corresponding to a binary parity signal PL, said points being defined by successive numerical samples, wherein said device comprises:

• (A) a sequential memory having three sections with an input which receives the sequence of numerical samples designated X.sub.n, in which n is a rank of the sample successively assuming integral values of 1 at N, and at least three outputs supplying, when the sample of rank n+1 is received at the input respectively:
• the sample of rank n, i.e. X.sub.n, the sample of rank n-1, i.e. X.sub.n-1 belonging to the same line as the sample received and the sample of rank n belonging to the preceding line, ie. X.sub.n ;
• (B) an examination circuit incorporating:
• means for detecting between two successive samples X.sub.n-1 and X.sub.n of the same line, the presence of a variation in the value of the sample exceeding a certain threshold and for producing a corresponding signal called "the vertical contour element" and designated EV.sub.n ;
• means for detecting between two samples X.sub.n ' and X.sub.n of the same rank but belonging to two adjacent lines the presence of a variation in the value of the sample exceeding the same threshold and for producing a corresponding signal called "horizontal contour element" and designated EH.sub.n ;
• two connected contour elements, an image contour then being defined by a system of connected contour elements;
• means for detecting the absence of a contour element at the point of rank n, said means supplying a signal designated HOLE.sub.n ;
• means for counting the total number of horizontal contour elements and the total number of vertical contour elements examined along a line for each connected zone, said numbers being converted into signals H and V at the end of the connected zone;
• means for detecting the connected horizontal and vertical contour elements and for detecting the systems of such connected elements along a line, said systems being called connected zones and each connected zone being between a first contour element and a last contour element, said means being able to supply a signal when a connected zone ends at a point of rank n, the signal being designated FZC.sub.n ;
• the examination circuit thus having the three inputs receiving the samples X.sub.n, X.sub.n-1 and X.sub.n ' and six outputs respectively supplying the signals EV.sub.n, EH.sub.n, V, H, FZC.sub.n, HOLE.sub.n ;
• (c) a loop functioning in a recursive manner and incorporating the means for calculating a magnitude representative of the contour and called state of the contour and designated E for storing the state
• E' obtained for the line preceding that which is examined and for calculating as a function of said state E and signals EH.sub.n, HOLE.sub.n, FZC.sub.n, V and H obtained for the examined line the new state E of the contour on said examined line.