Apparatus and method for extracting edges and lines

Claim 1

An apparatus for enhancing an image containing features, said image represented by pixel data, including feature as well as non-feature pixel data, said enhancement being produced without prior knowledge of said features, said apparatus comprising; sensor unit (24) for converting light energy from discrete pixels in said image into electrical signals, said pixels having defined locations in the X-Y plane; preprocessor unit (26) for digitizing said signals; means (28) for identifying curvature extrema as those points on a scan line where the intensity undergoes relatively large changes with respect to previous and subsequent pixels; means (28) for measuring the difference in intensity between pairs of curvature extrema and identifying those pairs of curvature extrema for which said difference exceeds a predetermined threshold; means (28) for identifying individual edge points as a point along the scan line between said identified pairs for curvature extrema, means (28) for identifying edge points along neighboring scan lines, first and second edge points being on first and second neighboring scan lines; means (28) for extrapolating a line segment between said first edge point and said second edge point if the pixel location difference between the first edge point on the first scan line and the second edge point on the second scan line is less than n pixels, where n is an integer; means (28) for calculating upper and lower line direction limits by extrapolating a line from said first edge point to a point X pixels greater than said second point, where X is an integer, and by extrapolating a line from said first edge point to a point X pixels less than said second point; means (28) for extrapolating a new line segment between said first edge point and a third edge point on a neighboring third scan line if that third edge point lies within said upper and lower line direction limits; and display unit (36) for creating an enhanced image containing only said identified edge points and line segments, wherein said enhanced image contains predominantly edge points and lines representing said features and is relatively free of said non-feature pixels.

Claim 5

The apparatus of anyone of the preceding claims, comprising memory unit (34) for storing said digitized signals, and means (32) coupled to said memory unit for detecting and measuring the intensity of said signals at discrete pixels along a plurality of scan lines throughout said image, said intensity values creating an intensity curve along the scan lines.

Claim 6

The apparatus of anyone of the preceding claims comprising means (28) for assigning the value of said electrical signal for each pixel to each defined location, and means (28) for selecting one linear scan line of said pixels in the X-Y plane.

Claim 7

The apparatus of anyone of the preceding claims wherein said means (24) for converting light energy is a CCD imager.

Claim 8

The apparatus of anyone of the preceding claims wherein said preprocessor unit (26) is a frame grabber preprocessor.

Claim 9

A method for enhancing an image containing features, said image represented by pixel data, including feature as well as non-feature pixel data, said enhancement being produced without prior knowledge of said features, said method comprising the steps of; a) converting light energy from an image into electrical signals corresponding to the intensity of said light energy in discrete pixels in said image, said pixels each having a defined location in the X-Y plane; b) identifying curvature extrema in a scan line by determining those pixels for which said electrical signal values change most rapidly with respect to the values for neighboring pixels along said scan line; c) measuring the difference in the magnitude of said electrical signal value between all pairs of curvature extrema along said scan line; d) determining selected pairs of curvature extrema for which said difference exceeds a predetermined threshold; e) identifying as an edge point a pixel along the scan line having an electrical signal value between the value for said identified pair, said pixel being located between said identified pair along said scan line; and displaying the X-Y location of said edge point; f) identifying edge points along neighboring scan lines, first and second edge points being along first and second neighboring scan lines; g) extrapolating a line segment between said first edge point and said second point if the pixel location difference between the first edge point on the first scan line and the second edge point on the second scan line is less than n pixels, where n is an integer; h) calculating upper and lower line direction limits by extrapolating a line from said first edge point to a point X pixels greater than said second point, where X is an integer, and by extrapolating a line from said first edge point to a point X pixels less than said second point; and i) extrapolating a new line segment between said first edge point and a third edge point on a neighboring third scan line if that third edge point lies within said upper and lower line direction limits.

Claim 13

The method of anyone of claims 9 to 12 wherein said step b) further comprises the step of determining those points where the derivative of the intensity curve exceeds a second threshold.

Claim 14

The method of anyone of claims 9 to 13 wherein said step e) further comprises the step of determining the point having an intensity value equal to the average intensity of the identified pair of curvature extrema.

Claim 15

The method according to anyone of claims 9 to 14 further comprising a step (j) of calculating a new upper or lower line direction limit by extrapolating a line from said first point to a point X pixels greater than said third edge point and by extrapolating a line from said first point to a point X pixel less than said third edge point, and using only those direction limits which create a narrower range of line direction limits.