Image processing method and apparatus for correlating a test image with a template

• US 5,982,945 A
• Filed: 01/13/1998
• Issued: 11/09/1999
• Est. Priority Date: 01/05/1996
• Status: Expired due to Term

• Current Assignee: Mcdonnell Douglas Corporation (The Boeing Co.)
• Original Assignee: Mcdonnell Douglas Corporation (The Boeing Co.)
• Inventors: Wright, Steven A., Neff, Michael G., Johnson, Ted L., Ratkowski, Victor E. Jr.
• Primary Examiner(s): Tran, Phuoc
• Assistant Examiner(s): Mariam, Daniel G.
• Application Number:
  US09/006,130
• Time in Patent Office: 665 Days
• Field of Search: 382/141, 382/142, 382/173, 382/180, 382/209, 382/217, 382/271, 382/172
• US Class Current: 382/271
• CPC Class Codes: F41G 7/007 Preparatory measures taken before the launching of the guided missiles
• CPC Class Codes: F41G 7/2226 comparing the observed data with stored target data, e.g. target configuration data
• CPC Class Codes: F41G 7/2253 Passive homing systems, i.e. comprising a receiver and do not requiring an active illumination of the target
• CPC Class Codes: F41G 7/2293 using electromagnetic waves other than radio waves
• CPC Class Codes: G06T 7/337 involving reference images or patches
• CPC Class Codes: G06V 10/751 Comparing pixel values or logical combinations thereof, or feature values having positional relevance, e.g. template matching
• CPC Class Codes: G06V 10/7515 Shifting the patterns to accommodate for positional errors
• CPC Class Codes: G06V 10/94 Hardware or software architectures specially adapted for image or video understanding

Abstract

The image correlation method and apparatus correlates or matches a test image with a template. The image correlation apparatus includes an image processor for partitioning the template into a number of labels, for determining the total number of pixels N_T which form the template and for determining the number of pixels N_i which form each of the labels i. The image correlation apparatus also includes comparison means for comparing the test image to the template. The comparison means determines, for each predetermined gray level j, the number of pixels of the test image N_j,i representative of a predetermined gray level j which correspond to a predetermined label i of the template. The comparison means also determines, for each predetermined gray level j, the number of pixels of the test image N_j representative of a predetermined gray level j which correspond to the template. The image correlation apparatus further includes correlation means for determining the correlation X between the test image and the template according to a predetermined equation which is based, at least in part, upon N_j,i, N_j, N_i and N_T. The image correlation apparatus can also include an address generator for creating a number of relative offsets between the template and the test image. Thus, the test image can be compared to the template at each relative offset and the relative offset which provides the greatest correlation therebetween can be determined. Consequently, the test image and the template can be effectively matched such that a preselected object designated within the template can be located and identified within the test image.

Claims

1. A method of partitioning a template into a plurality of labels, wherein the template is comprised of a plurality of pixels representative of respective predetermined gray levels, the method comprising the steps of:

dividing the plurality of predetermined gray levels into a plurality of bins, wherein each bin includes a range of gray levels;

determining, for each of the plurality of bins, an actual count of the number of pixels which are representative of gray levels within the range of gray levels included within the respective bin;

determining, for each of the plurality of bins, if the actual count for the respective bin is less than a predetermined minimum count;

assigning the predetermined minimum count to each bin which has an actual count determined by said count determining step which is less than the predetermined minimum count;

redefining at least some of the bins to include different ranges of gray levels if the greater of the predetermined minimum count or the actual count for each respective bin falls outside a predetermined range; and

repeating said determining, assigning and redefining steps until the greater of the predetermined minimum count or the actual count for each respective bin is within the predetermined range, wherein the pixels which are representative of gray levels within a respective bin form a label.

2. A method according to claim 1 further comprising the steps of:

determining the maximum number of pixels of the template which are representative of a single predetermined gray level; and

computing the predetermined minimum count to be equal to a predetermined percentage of the maximum number of pixels which are representative of a single predetermined gray level.

3. A method according to claim 2 wherein the predetermined percentage is between about 15% and about 25%.

4. A method according to claim 1 further comprising the step of determining the number of pixels of the template which are representative of each of the predetermined gray levels.

5. A method according to claim 1 wherein said determining, assigning and redefining steps are repeated until the greater of the predetermined minimum count or the actual count for each respective bin is equal.

6. An apparatus for partitioning a template into a plurality of labels, wherein the template is comprised of a plurality of pixels representative of respective predetermined gray levels, the apparatus comprising:

means for dividing the plurality of predetermined gray levels into a plurality of bins, wherein each bin includes a range of gray levels;

means, responsive to said dividing means, for determining, for each of the plurality of bins, an actual count of the number of pixels which are representative of gray levels within the range of gray levels included within the respective bin;

comparison means responsive to said actual count determining means, for determining, for each of the plurality of bins, if the actual count for the respective bin is less than a predetermined minimum count;

means, responsive to said comparison means, for assigning the predetermined minimum count to each bin which has an actual count which is less than the predetermined minimum count; and

means, responsive to said actual count determining means and said assigning means, for redefining at least some of the bins to include different ranges of gray levels if the greater of the predetermined minimum count or the actual count for each respective bin is within a predetermined range,

wherein said actual count determining means, said comparison means said assigning means and said redefining means repeatedly process the pixels in accordance with the redefined bins until the greater of the predetermined minimum count or the actual count for each respective bin is within the predetermined range, wherein the pixels which are representative of gray levels within a respective bin form a label.

7. An apparatus according to claim 6 further comprising:

means for determining the maximum number of pixels of the template which are representative of a single predetermined gray level; and

means, responsive to said means for determining the maximum number of pixels, for computing the predetermined minimum count to be equal to a predetermined percentage of the maximum number of pixels which are representative of a single predetermined gray level.

8. An apparatus according to claim 7 wherein the predetermined percentage is between about 15% and about 25%.

9. An apparatus according to claim 6 wherein said actual count determining means, said comparison means, said assigning means and said redefining means repeatedly process the pixels in accordance with the redefined bins until the greater of the predetermined minimum count or the actual count for each respective bin is equal.