Method and a circuit for determining a contour in an image

Claim 1

In a method of determining a contour-defining angle formed by a contour in an image within a relatively small region thereof with a predetermined direction, the contour being defined by the transition from a light area to a dark area within said region, the steps comprising, selecting said region so that said contour passes as closely as possible through a center thereof, subdividing said region into a number of sectors of substantially equal areas distributed substantially symmetrically about said center, and separated from one another by respective separation lines, aid number being an even number and at least four, one of said separation lines coinciding with said predetermined direction, obtaining brightness signals from each of said sectors in dependence of the proportion of the dark-to-light areas extending over each respective sector, generating difference signals from respective oppositely disposed sectors, one of said difference signals being associated with said transition from said light area to said dark area having a value below a maximum value obtained from each of the remaining difference signals, save the difference signal associated with the transition from said dark area to said light area, thereby identifying the sector in which the transition from said light area to said dark area occurs, and determining a first angle-defining quotient of the difference signal obtained, on one hand, from the so identified sector and the sector adjacent thereto as viewed along a prearranged angular direction, and, on the other hand, from one of said difference signals having said maximum value, whereby the contour-defining angle is obtained as the sum of said first angle and a second angle which is subtended between said predetermined direction and said one separation line, as viewed along said prearranged angular direction.

Claim 8

An apparatus for determining a contour-defining angle formed by a contour in an image within a relatively small region thereof with a predetermined direction, the contour being defined by the transition from a light area to a dark area, said region including a center, comprising in combination, scanning means, including photoelectric transducer means for obtaining signals from a number of sectors within said region having substantially equal areas, and being distributed substantially symmetrically about a center thereof, said number being even and at least four, signal-difference forming means connected to said scanning means for forming difference signals from respective oppositely disposed sectors, and sectors containing said contour and respective sectors adjacent said contour-containing sectors, contour-containing sector recognition means connected to said signal-difference forming means for generating a contour-recognition signal for the sector containing the contour, a contour-defining angle calculator connected to said signal-difference forming means and to said contour-containing sector recognition means for determining the contour-defining angle, and contour-passing-through-center recognition means connected to said scanning means for determining whether the contour passes through said center, whereby, upon said contour passing through said center, said contour-differing angle calculator may be enabled by said contour-passing-through center recognition means to determine said contour-defining angle.

Claim 9

An apparatus for determining a contour-defining angle formed by a contour in an image within a relatively small region thereof with a predetermined direction, the contour being defined by the transition from a light area to a dark area, said region including a center, comprising in combination, scanning means, including photoelectric transducer means for obtaining signals from a number of sectors within said region having substantially equal areas, and being distributed substantially symmetrically about a center thereof, said number being even and at least four, signal-difference forming means connected to said scanning means for forming difference signals from respective oppositely disposed sectors, and sectors containing said contour and respective sectors adjacent said contour-containing sectors, contour-containing sector recognition means connected to said signal-difference forming means for generating a contour-recognition signal for the sector containing the contour, a contour-defining angle calculator connected to said signal-difference forming means and to said contour-containing sector recognition means for determining the contour-defining angle, and contour-passing-through-center recognition means connected to said scanning means for determining whether the contour passes through said center, whereby, upon said contour passing through said center, said contour-differing angle calculator may be enabled by said contour-passing-through center recognition means to determine said contour-defining angle.