Process and device for detection of straight-line segments in a stream of digital data that are representative of an image in which the contour points of said image are identified

A process for detection of straight-line segments in a stream of digital data that are representative of an image (m, n) in which the contour points of said image each defined by the modulus and the orientation, of their gradient in relation to a horizontal axis are identified, the process comprising:

• storing the stream of digital data in the form of two successive lines, each of n points P(i, j), with 1≦i≦m and 1≦j≦n, and for each of the lines the n points of said line are extracted successively, and for each point Pc(i, j) extracted, the so-called current point:
• the three points having inferior coordinates Pa(i−1, j−1), Pb(i, j−1), Pd(i−1, j) directly neighbouring said current point are extracted,
• successively comparing the value of the orientation of the gradient of the current point Pc with that of the neighbouring points Pa, Pb and Pd, and comparing the values of the orientations of the gradients of the points Pb and Pd,
• validating the result of a comparison, representative of a connection between two points, if said points are contour points and if the difference between the values of the orientation of their gradient is less than or equal to a predetermined value k,
• when the result of a comparison is validated the coordinates of the point of the connection having inferior coordinates, the so-called start-point, are copied over to those of the point of said connection having superior coordinates, the so-called end-point, and erasing the coordinates of the start-point from the memory, unless said start-point has been identified as being an origin point of a straight-line segment,
• it is verified whether solely the point Pa (i−1, j−1) is a contour point amongst the four points Pa, Pb, Pc, Pd extracted, and in the affirmative case the size of the straight-line segment for which said point Pa is the final point is calculated and the coordinates of the origin point and of the final point and the orientation of said straight-line segment, if its size is greater than a predetermined threshold, are saved.