Image correlation calculation apparatus

• US 5,063,602 A
• Filed: 03/26/1991
• Issued: 11/05/1991
• Est. Priority Date: 04/14/1987
• Status: Expired due to Fees

• Current Assignee: Nippon Sheet Glass Company Limited
• Original Assignee: Nippon Sheet Glass Company Limited
• Inventors: Nishi, Hisami, Peppers, Norman A., Young, James R., Pierce, Gerald A.
• Primary Examiner(s): Razavi, Michael
• Application Number:
  US07/679,161
• Time in Patent Office: 224 Days
• Field of Search: 382/31, 382/32, 382/33, 382/68, 382/46, 350/376, 350/162.13, 340/784, 340/765
• US Class Current: 382/213
• CPC Class Codes: G06V 10/88 Image or video recognition using optical means, e.g. reference filters, holographic masks, frequency domain filters or spatial domain filters

Abstract

In an image correlation calculation apparatus for optically calculating correlations between reference patterns and an image such as a character or any other figure, the image such as the character or any other figure subjected to correlation calculations is optically multiplied by a multiplier to form simultaneously in parallel a plurality of optical pattern images of a substantially identical shape, and optical correlation calculation between the plurality of optical pattern images and the reference patterns formed on various types of reference masks is performed individually and instantaneously, the various type of reference masks being arranged at a position spaced apart by a predetermined distance from the plurality of optical pattern image, thereby detecting beams emitted through the various types of reference masks. Image multiplication, optical correlation calculation, and transmission of the result of the optical correlation calculation to the photosensors can be simultaneously performed at a light propagation time. The apparatus structure can be simplified at low cost, and image correlation operations can be performed at high speed.

Claims

1. An image correlation calculation apparatus comprising:

a multiplier for optically multiplying an image subjected to correlation calculations to form a plurality of optical pattern images of a substantially identical shape;

a plurality of reference masks respectively having reference patterns subjected to correlation calculations with the optical pattern images, said reference masks being arranged at a position spaced apart by a predetermined distance from said plurality of optical pattern images in one-to-one correspondence therewith so that beams from all points of each optical pattern image are incident on all points of the corresponding reference pattern;

a plurality of condenser lenses which are arranged to have parallel optical axes at a predetermined position in one-to-one correspondence with said reference masks for condensing the beams of each optical pattern image passing through said reference masks whereby an optical correlation calculation between said optical pattern image and said reference pattern can be performed instantaneously, said predetermined distance satisfying the inequality D<

2d₁ {p/(1-p)} where d₁ is the distance from said multiplier to said optical pattern images and p is the ratio of the size of said optical pattern images to the size of the aperture of said condenser lenses; and

photodetecting means for detecting the beams which are emitted from the plurality of condenser lenses, whereby an optical correlation calculation between said optical pattern image and said reference pattern is performed instantaneously without having to shift said reference masks with respect to the optical pattern image.

2. An apparatus according to claim 1, wherein the predetermined distance falls within a range of 0.1 to 10 mm.

3. An apparatus according to claim 1, wherein the predetermined distance falls within a range of 0.3 to 5 mm.

4. An apparatus according to claim 1, wherein said various types of reference masks are constituted as fixed masks in which said various types of reference patterns are respectively predetermined patterns which cannot change to other patterns.

5. An apparatus according to claim 1, wherein said multiplier comprises:

a projection lens located at a position spaced apart by a focal length thereof from a position of the image subjected to correlation calculation; and

a plurality of image formation lenses which are arranged to have parallel optical axes at a position spaced apart by a distance required to form an image from the projection lens, and are formed in one-to-one correspondence with said various types of reference masks, said plurality of image formation lenses being adapted to form the plurality of optical pattern images of a substantially identical shape upon reception of collimated beams from said projection lens.

6. An apparatus according to claim 5, wherein said various types of reference masks are formed as a two-dimensional mask array on a common optical member in one-to-one correspondence with said plurality of optical pattern images.

7. An apparatus according to claim 6, wherein said photodetecting means comprises a plurality of photosensors in one-to-one correspondence with said plurality of condenser lenses so as to individually receive and detect the beams from said plurality of condenser lenses.

8. An apparatus according to claim 7, wherein said mask array is arranged in contact with said plurality of condenser lenses so that optical axes of said reference masks are respectively aligned with those of said condenser lenses.

9. An apparatus according to claim 8, wherein light-receiving surface of said plurality of photosensors constituting said photodetecting means are located at a position of a rear-side focal point of said plurality of said condenser lenses.

10. An apparatus according to claim 9, wherein said plurality of photosensors constituting said photodetecting means comprise image sensors, respectively.

11. The apparatus of claim 1, wherein said multiplier has a focal length and wherein said predetermined distance is greater than said focal length so that the optical pattern images incident on said reference masks are out of focus.

12. A method for image correlation calculation, comprising the steps of:

passing an image subjected to correlation calculations through an optical multiplier, thereby optically multiplying said image to form a plurality of optical pattern images of a substantially identical shape;

positioning a plurality of reference masks, respectively having reference patterns subjected to correlation calculations with the optical pattern images, at a position spaced apart by a predetermined distance from said plurality of optical pattern images in one-to-one correspondence therewith so that beams from all points of each optical pattern image are incident on all points of the corresponding reference pattern, whereby an optical correlation calculation between said optical pattern image and said reference pattern can be performed instantaneously;

condensing the beams of each optical pattern image passing through said reference masks using a plurality of condenser lenses having an aperture, wherein said predetermined distance satisfies the inequality D<

2d₁ {p/(1-p)} where d₁ is the distance from said optical multiplier to said optical pattern images and p is the ratio of the size of said optical pattern images to the size of said aperture; and

detecting the beams which are condensed, whereby an optical correlation calculation between said optical pattern image and said reference pattern is performed instantaneously without having to shift said reference masks with respect to the optical pattern image.