Video safety detector with shadow elimination

• US 6,469,734 B1
• Filed: 04/29/2000
• Issued: 10/22/2002
• Est. Priority Date: 04/29/2000
• Status: Active Grant

• Current Assignee: Cognex Corporation
• Original Assignee: Cognex Corporation
• Inventors: Wolff, Robert, Schatz, David A., Silver, William, Nichani, Sanjay
• Primary Examiner(s): DIEP, NHON THANH
• Application Number:
  US09/563,010
• Time in Patent Office: 906 Days
• Field of Search: H04/N.718, 348/143, 348/150, 348/151, 348/152-155, 348/156, 348/159, 348/161, 348/164, 348/169
• US Class Current: 348/152
• CPC Class Codes: H04N 7/188 Capturing isolated or intermittent images triggered by the occurrence of a predetermined event, e.g. an object reaching a predetermined position signal generation from motion picture films H04N5/253

Abstract

A two-dimensional (2-D) machine-vision safety-solution involving a method and apparatus for performing high-integrity, high efficiency machine vision. The machine vision safety solution digitally filters a configurable number of time-sequenced images of a viewed area to create a filtered image. A textured background is used as a static target and viewed under ambient light, or alternatively a texture is observed under IR light. An artificial texture can be created with a particularized pattern. Each new image is then compared to the previously created model and a pixel-oriented difference image is calculated. The difference image is then processed for segmentation features attributable to an intruder object. For segmentation results that exceed a predetermined threshold, an alarm condition is set.

Claims

1. A method of detecting an intruding object in a space comprising the steps of:

applying a textured background on said space;

acquiring a digital source image of said space;

generating a background image by processing said source image using a low pass filter;

comparing said source image with said background image using a digital subtraction step to form a difference image;

constructing a mask image by segmenting said difference image;

combining said mask image with said background image to form a masked background image;

performing an edge detection procedure on said masked background image to determine edge data;

performing a gradient computation procedure on said source image to generate a gradient image; and

performing a texture comparison procedure on said gradient image and said edge data.

2. The method according to claim 1 wherein said steps of generating and comparing comprise a high pass filter process.

3. The method according to claim 2 wherein said mask image comprises indications defining pass areas as blobs from said high pass filter and defining clear areas as non-blob areas from said high pass filter.

4. The method according to claim 1 further comprising the step of taking an absolute value of said difference image to form an absolute difference image, wherein said step of segmenting is performed on said absolute difference image rather than on said difference image.

5. The method according to claim 1 wherein said step of segmenting further comprises the steps of:

characterizing contiguous related pixels;

determining areas of contiguous related pixels; and

comparing said areas with threshold limits.

6. The method according to claim 1 further comprising the step of providing notification output if said texture comparison procedure finds a discrepancy between said edge data and said gradient images which discrepancy exceeds a predetermined threshold.

7. The method according to claim 1 wherein said step of segmenting is performed using a watershed process.

8. The method according to claim 1 further comprising the step of illuminating said space with diffuse light.

9. The method according to claim 2 wherein said diffuse light is provided by a light source mounted proximate to said camera.

10. The method according to claim 1 wherein said source image comprises a set of time sequenced images.

11. The method according to claim 1 further comprising a step of illuminating said space with near IR light.

12. The method according to claim 11 wherein said step of acquiring a digital source image further comprising a step of filtering light reflected from said space using an IR bandpass filter.

13. The method according to claim 11 wherein said textured background comprises texture having pre-selected IR reflectivity.

14. The method according to claim 1 wherein said textured background comprises a high spatial frequency texture.

15. The method according to claim 1 wherein said textured background comprises a perimeter of said space.

16. The method according to claim 1 wherein said step of performing a gradient computation procedure comprises computing a magnitude and direction of a first derivative at each point in said source image.

17. The method according to claim 1 wherein said step of performing a gradient computation procedure comprises convolving said source image with standard Sobel kernels.

18. A machine vision intrusion detection apparatus comprising:

at least one image acquisition device arranged to acquire an image of a space;

at least one light source arranged to illuminate at least part of said space;

at least one video processor in communication with said at least one image acquisition device;

wherein said at least one video processor further comprises;

an image processor component in communication with said image acquisition device;

wherein said image processor component further comprises a low pass filter component in communication with said image acquisition device and receiving a source image therefrom;

a comparison component in communication with said image acquisition device and receiving said source image therefrom, said comparison component also in communication with said low pass filter component and receiving a background image therefrom;

a segmentation component in communication with said comparison component and receiving a difference image therefrom;

an edge detection component in communication with said segmentation component and receiving a mask image therefrom, said edge detection component also in communication with said low pass filter and receiving a background image therefrom;

a gradient computation component in communication with said image acquisition device and receiving a source image therefrom; and

a texture comparison component in communication with said edge detection component and receiving edge data therefrom, said texture comparison component also in communication with said gradient computation component and receiving gradient images therefrom.

19. The apparatus according to claim 18:

wherein said light source comprises a near IR light source; and

wherein said image acquisition device is configured with an IR band-pass filter to acquire reflected near IR light and reject light outside of the near IR frequency band.