Method and system for recognizing a rotated image pattern with reduced processing time and memory space

• US 6,226,417 B1
• Filed: 08/04/1998
• Issued: 05/01/2001
• Est. Priority Date: 08/04/1997
• Status: Expired due to Term

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Hirano, Akihiko, Yamagata, Hideaki, Kuranaga, Tatsuya, Tachikawa, Michiyoshi
• Primary Examiner(s): Mancuso, Joseph
• Assistant Examiner(s): Kassa, Yosef
• Application Number:
  US09/128,836
• Time in Patent Office: 1,001 Days
• Field of Search: 382/289, 382/296, 382/297, 382/216, 382/209, 382/286, 382/291
• US Class Current: 382/289
• CPC Class Codes: G06T 3/60 Rotation of whole images or parts thereof
• CPC Class Codes: G06V 10/435 Computation of moments

Abstract

An image pattern recognition process and system recognize a rotated predetermined image pattern with reduced processing time and memory requirements based upon the efficient use of the Zernike Moment.

Claims

1. A method of determining a rotational angle of an image pattern having an outer boundary, comprising:

inputting an input image pattern and a radial polynomial table containing sets of Zernike Moment (ZM) intermediate values for a predetermined specific size of the input image pattern, each set containing the ZM intermediate values each at a predetermined rotational angle for a predetermined periodicity;

determining a plurality of Zernike Moment (ZM) values by multiplying a predetermined set of the ZM intermediate values by pixel values at predetermined equidistant locations from a center of the input image pattern;

assigning an evaluation value for each of the ZM values by multiplying the ZM value and a corresponding periodicity; and

determining a rotational angle of the input image pattern based upon a largest one of the evaluation values.

2. The method of determining a rotational angle according to claim 1 wherein the plurality of the Zernike Moment (ZM) values are each compared to a predetermined corresponding range of the ZM values.

3. The method of determining a rotational angle according to claim 2 wherein the evaluation value is assigned only when each of the ZM values is within the predetermined corresponding range.

4. The method of determining a rotational angle according to claim 1 wherein candidates for the rotational angle is determined for the periodicity.

5. The method of determining a rotational angle according to claim 1 wherein the rotational angle is verified after it is determined.

6. A system for determining a rotational angle of an image pattern having an outer boundery, comprising:

an input unit for inputting an input image pattern and a radial polynomial table containing sets of Zernike Moment (ZM) intermediate values for a predetermined specific size of the input image pattern, each set containing the ZM intermediate values each at a predetermined rotational angle for a predetermined periodicity;

a Zernike Moment generation unit connected to said input unit for determining a plurality of Zernike Moment (ZM) values by multiplying a predetermined set of the ZM intermediate values by pixel values at predetermined equidistant locations from a center of the input image pattern;

an evaluation unit connected to said Zernike Moment generation unit for assigning an evaluation value for each of the ZM values by multiplying the ZM value and a corresponding periodicity; and

a rotational angle determination unit connected to said evaluation unit for determining a rotational angle of the input image pattern based upon a largest one of the evaluation values.

7. The system for determining a rotational angle according to claim 6 wherein said evaluation unit compares each of the plurality of the Zernike Moment (ZM) values to a predetermined corresponding range of the ZM values.

8. The system for determining a rotational angle according to claim 7 wherein said evaluation unit assigns the evaluation value only when each of the ZM values is within the predetermined corresponding range.

9. The system for determining a rotational angle according to claim 6 wherein said rotational angle determination unit determines a plurality of the rotational angles as candidates for the periodicity.

10. The system for determining a rotational angle according to claim 6 wherein said rotational angle determination unit verifies the rotational angle after it is tentatively determined.