Image recognition edge detection method and system

• US 5,115,477 A
• Filed: 02/07/1991
• Issued: 05/19/1992
• Est. Priority Date: 03/31/1988
• Status: Expired due to Fees

• Current Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Original Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Inventors: Groezinger, John L.
• Primary Examiner(s): Moore, David K.
• Assistant Examiner(s): Couso, Jose L.
• Application Number:
  US07/652,409
• Time in Patent Office: 467 Days
• Field of Search: 382/1, 382/8, 382/22, 382/41, 382/48, 382/50, 358/101, 358/106, 358/107
• US Class Current: 382/199
• CPC Class Codes: G06T 7/12 Edge-based segmentation
• CPC Class Codes: G06T 7/194 involving foreground-background segmentation

Abstract

A system and method for delineating the edges of an object in an image frame formed of a two dimensional array of pixels represented by a plurality of gray scale values representing the gray scales of the pixels. A reference contrast level based on the distribution of contrast levels between contiguous pixels is established, and the contrast levels of pairs of pixels in square groupings of four contigous pixels are compared with the reference contrast level. A two dimensional array of elements corresponding to the arrangement of the square groupings of pixels is formed in which each element has a first value only if the contrast level between a pair of pixels in a square grouping is greater than the reference contrast level.

Claims

1. In a system in which an image frame formed of a two dimensional array of pixels is represented by a plurality of gray scale values, each gray scale value representing a gray scale of a separate pixel in the image frame, means for determining the edges of an object in the image frame, comprising:

reference determining means for establishing a reference contract level based on the distribution of differences between gray scale and values of pairs of contiguous pixels in the image frame said reference determining means comprising means for examining the distribution of differences between gray scale values of pair of contiguous pixels, and establishing as the reference contrast level the difference level which is the last of a predetermined number of successive difference levels each of which exceeds the next smaller difference level by at least a predetermined amount, said reference determining means comprising additional means for examining groups of gray scale values, the groups corresponding to square groupings of four contiguous pixels, and, for each group, calculating the differences between every combination of pairs of gray scale values, said means for examining groups of gray scale values further determining the distribution of differences between gray scale values of pairs of contiguous pixels; and

means for examining groups of gray scale values, the groups corresponding to square groupings of four contiguous pixels, and producing a two dimensional array of elements arranged to correspond to the arrangement of square groupings of four contiguous pixels, each element in the array having either a first or second value, the first value occurring only if the difference between gray scale values corresponding to a pair of pixels in a square grouping of four contiguous pixels is greater than the reference contrast level, whereby the first values are arranged to represent the edges of the object in the image frame.

2. The system of claim 1 wherein said means for examining groups of gray scale values sequentially examines square groupings of four contiguous pixels by row and column of groups of pixels in the order of the difference between the gray scale values of the upper left and upper right pixels, the upper left and lower right pixels, the upper left and lower left pixels and the lower left and upper right pixels for each of the square groupings, said means for examining groups of gray scale values further being operable to produce the first value for the element in the two dimensional array if any of the differences for the corresponding square grouping of pixels is at least as great as the reference contrast level, and to produce the second value for the element in the two dimensional array if all of the differences for the corresponding square grouping of pixels are less than the reference contrast level.

3. A method for determining and representing the edges of an object in an image frame formed of a two dimensional array of pixels represented by a plurality of gray scale values, each gray scale value representing the gray scale of a separate pixel in the image frame, the method comprising the steps of:

establishing a reference contrast level based on the distribution of differences between gray scale values of pairs on continuous pixels in the image frame, the step of establishing a reference contrast level comprising the steps of examining the distribution of differences between gray scale values and establishing as the reference contrast level the difference level which is the last of a predetermined number of successive difference levels each of which exceeds the next smaller difference level by at least a predetermined amount;

examining groups of gray scale values corresponding to square groupings of four contiguous pixels, the step of examining the distribution of differences between gray scale values including the steps of examining groups of gray scale values corresponding to square groupings of four contiguous pixels, calculating for each group the differences between each combination of pairs of gray scale values, determining the distribution of differences in gray scale values in order of increasing difference, examining the distribution of differences in gray scale values for a plurality of successive difference levels, each of which exceeds the next smaller difference level by at least a predetermined amount and selecting the difference level which is the last of a predetermined number of difference levels in the succession as the reference contrast level;

calculating for each group the differences between each combination of pairs of gray scale values; and

producing a two dimensional array of elements arranged to correspond to the arrangement of square groupings of four contiguous pixels, each element in the array of elements having either a first or a second value, the first value occurring only if a difference between gray scale values of a pair of pixels in the corresponding square grouping is at least as great as the reference contrast level, whereby the first values are arranged to represent the edges of the object in the image frame.

4. The method of claim 3 wherein the step of examining groups of gray scale values comprises sequentially examining square groupings of four contiguous pixels in sequence by row and column of groupings of pixels and calculating the differences in gray scale values in the order of the upper left and upper right pixels, the upper lift and lower right pixels, the upper left and lower left pixels and the lower left and upper right pixels for each of the square groupings.