Technique for differencing an image

• US 6,421,462 B1
• Filed: 02/06/1998
• Issued: 07/16/2002
• Est. Priority Date: 02/06/1998
• Status: Expired due to Fees

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Compaq Computer Corporation (HP Inc.)
• Inventors: Christian, Andrew D., Avery, Brian L.
• Primary Examiner(s): Mehta, Bhavesh
• Assistant Examiner(s): Kassa, Yosef
• Application Number:
  US09/020,035
• Time in Patent Office: 1,621 Days
• Field of Search: 382/162, 382/167, 382/165, 382/219, 382/164, 382/106, 382/144, 382/218, 382/220, 382/283, 382/130, 358/518, 358/520, 358/517, 345/2.2, 345/72, 348/631, 348/717, 340/146.2, 340/870.01
• US Class Current: 382/219
• CPC Class Codes: G06T 7/254 involving subtraction of images
• CPC Class Codes: G06V 40/103 Static body considered as a whole, e.g. static pedestrian or occupant recognition
• CPC Class Codes: G08B 13/19602 Image analysis to detect motion of the intruder, e.g. by frame subtraction
• CPC Class Codes: G08B 13/19604 involving reference image or background adaptation with time to compensate for changing conditions, e.g. reference image update on detection of light level change
• CPC Class Codes: G08B 13/19608 Tracking movement of a target, e.g. by detecting an object predefined as a target, using target direction and or velocity to predict its new position

Abstract

A technique for differencing an image is disclosed. In one embodiment, the technique is realized by measuring light values in a scene to generate a first image and a second image. The first image is separated into first luminance and chrominance components, and the second image is separated into second luminance and chrominance components. A difference is determined between the first and the second luminance components to generate a luminance mask. Similarly, a difference is determined between the first and the second chrominence components to generate a chrominance mask. The luminance mask and the chrominence mask are combined to determine a difference between the first and the second images.

Claims

1. A method for differencing images, said method comprising the steps of:

measuring light values by one camera in a scene to generate a first image and a second image;

wherein the first and the second image generations are separated in time,

separating the first image into first luminance and chrominance components and the second image into second luminance and chrominance components;

determining a difference between the first and second luminance components, wherein areas of the scene having a substantial difference define a luminance mask;

determining a difference between the first and second chrominance components, wherein areas of the scene having a substantial difference define a chrominance mask; and

combining into a single mask the luminance mask and chrominance mask to determine a difference between the first and second images, and wherein the single mask defines areas of the scene occupied by an object to be identified.

2. The method of claim 1, wherein the first chrominance component includes a first color component and a second color component and the second chrominance component includes a third color component and a fourth color component, said method further comprising the steps of:

determining a difference between the first color component and the third color component to generate a first difference value; and

determining a difference between the second color component and the fourth color component to generate a second difference value.

3. The method of claim 2, further comprising the step of:

combining the first difference value and the second difference value to generate the chrominance mask.

4. The method of claim 3, wherein the first difference value is weighted differently than the second difference value when combining the first difference value and the second difference value to generate the chrominance mask.

5. The method of claim 3, further comprising the steps of:

combining the first difference value and the second difference value to generate a third difference value; and

thresholding the third difference value to generate the chrominance mask.

6. The method of claim 5, wherein the first difference value is weighted differently than the second difference value when combining the first difference value and the second difference value to generate the third difference value.

7. The method of claim 1, wherein the difference between the first and the second luminance components is thresholded to generate the luminance mask, and the difference between the first and the second chrominance components is thresholded to generate the chrominance mask.

8. A method for differencing an image, said method comprising the steps of:

obtaining a first representation of a plurality of first pixels representing a scene at a first point in time, each of the first pixels having a first pixel parameter of a respective first value and a second pixel parameter of a respective second value;

determining a first difference value for each of the first pixels representing a difference between the first value of the first pixel parameter of each of the first pixels and a third value of the first pixel parameter of a corresponding one of a plurality of second pixels representing the scene at a second point in time;

determining a second difference value for each of the first pixels representing a difference between the second value of the second pixel parameter of each of the first pixels and a fourth value of the second pixel parameter of a corresponding one of the plurality of second pixels representing the scene at the second point in time;

determining a third difference value for each of the first pixels by combining the first difference value of a corresponding one of the plurality of first pixels and the second difference value of a corresponding one of the plurality of first pixels; and

identifying a plurality of third pixels, each of the third pixels being identified based upon a relation between the third difference value for a corresponding first pixel and a first threshold value; and

producing a second representation of the plurality of third pixels to thereby represent a difference in the scene at the first point in time as compared to the scene at the second point in time.

9. The method of claim 8, wherein the relation between the third difference value for a corresponding first pixel and the first threshold value is whether the third difference value for a corresponding first pixel exceeds the first threshold value.

10. The method of claim 8, wherein the third difference value for each of the first pixels is determined by combining the first difference value of a corresponding one of the plurality of first pixels and the second difference value of a corresponding one of the plurality of first pixels such that the first difference value of a corresponding one of the plurality of first pixels is weighted differently than the second difference value of a corresponding one of the plurality of first pixels.

11. A method for differencing an image, said method comprising the steps of:

obtaining a first representation of a plurality of first pixels representing a scene at a first point in time, each of the first pixels having a first pixel parameter of a respective first value and a second pixel parameter of a respective second value;

determining a first difference value for each of the first pixels representing a difference between the first value of the first pixel parameter of each of the first pixels and a third value of the first pixel parameter of a corresponding one of a plurality of second pixels representing the scene at a second point in time;

determining a second difference value for each of the first pixels representing a difference between the second value of the second pixel parameter of each of the first pixels and a fourth value of the second pixel parameter of a corresponding one of the plurality of second pixels representing the scene at the second point in time;

identifying a plurality of third pixels, each of the third pixels being identified based upon a relation between the first difference value for a corresponding first pixel and a first threshold value;

identifying a plurality of fourth pixels, each of the fourth pixels being identified based upon a relation between the second difference value for a corresponding first pixel and a second threshold value; and

producing a second representation by combining the plurality of third pixels and the plurality of fourth pixels to thereby represent a difference in the scene at the first point in time as compared to the scene at the second point in time.

12. The method of claim 11, wherein the relation between the first difference value for a corresponding first pixel and the first threshold value is whether the first difference value for a corresponding first pixel exceeds the first threshold value.

13. The method of claim 11, wherein the relation between the second difference value for a corresponding first pixel and the second threshold value is whether the second difference value for a corresponding first pixel exceeds the second threshold value.

14. The method of claim 11, wherein the first representation is a digital representation, and obtaining the first representation includes imaging the scene.

15. The method of claim 11, wherein the first pixel parameter is luminance and the second pixel parameter is a single color channel.

16. The method of claim 11, wherein the first pixel parameter is a first color characteristic and the second pixel parameter is a second color characteristic.

17. The method of claim 11, further comprising the steps of:

producing a third representation of the plurality of third pixels; and

producing a fourth representation of the plurality of fourth pixels;

wherein the second representation is produced by combining the third representation and the fourth representation.

18. The method of claim 11, further comprising the step of:

identifying a plurality of fifth pixels, each of the fifth pixels being identified by combining a corresponding one of the plurality of third pixels and a corresponding one of the plurality of fourth pixels;

wherein the second representation is produced from the plurality of fifth pixels.

19. The method of claim 11, wherein each of the first pixels has a third pixel parameter of a respective fifth value, each of the second pixels has a respective sixth value of the third pixel parameter, and further comprising the steps of:

determining a third difference value for each of the first pixels representing a difference between the fifth value of the third pixel parameter of each of the first pixels and the sixth value of the third pixel parameter of a corresponding one of the plurality of second pixels;

determining a fourth difference value for each of the first pixels by combining the second difference value of a corresponding one of the plurality of first pixels and the third difference value of a corresponding one of the plurality of first pixels; and

identifying a plurality of fifth pixels, each of the fifth pixels being identified based upon a relation between the fourth difference value of a corresponding first pixel and a third threshold value;

wherein the second representation is produced by combining the plurality of third pixels and the plurality of fifth pixels.

20. The method of claim 19, wherein the relation between the fourth difference value for a corresponding first pixel and the third threshold value is whether the fourth difference value for a corresponding first pixel exceeds the third threshold value.

21. The method of claim 19, wherein the first pixel parameter is a first color characteristic, the second pixel parameter is a second color characteristic, and the third pixel parameter is a third color characteristic.

22. The method of claim 19, wherein the first pixel parameter is luminance, the second pixel parameter is a relative amount of blue light, and the third pixel parameter is a relative amount of red light.

23. The method of claim 19, further comprising the steps of:

producing a third representation of the plurality of third pixels; and

producing a fourth representation of the plurality of fifth pixels;

wherein the second representation is produced by combining the third representation and the fourth representation.

24. The method of claim 19, further comprising the step of:

identifying a plurality of sixth pixels, each of the sixth pixels being identified by combining a corresponding one of the plurality of third pixels and a corresponding one of the plurality of fifth pixels;

wherein the second representation is produced from the plurality of sixth pixels.

25. The method of claim 19, wherein the fourth difference value for each of the first pixels is determined by combining the second difference value of a corresponding one of the plurality of first pixels and the third difference value of a corresponding one of the plurality of first pixels such that the second difference value of a corresponding one of the plurality of first pixels is weighted differently than the third difference value of a corresponding one of the plurality of first pixels.

26. The method of claim 11, further comprising the step of:

obtaining a third representation of the plurality of second pixels to represent the scene at the second point in time.

27. An apparatus for differencing images, said apparatus comprising:

a camera for measuring light values in a scene to generate a first image and a second image;

wherein the first and the second image generations are separated in time, and at least one processor for;

separating the first image into first luminance and chrominance components and the second image into second luminance and chrominance components;

determining a difference between the first and second luminance components, wherein areas of the scene having a substantial difference define a luminance mask;

determining a difference between the first and second chrominance components, wherein areas of the scene having a substantial difference define a chrominance mask; and

combining into a single mask the luminance mask and chrominance mask to determine a difference between the first and second images, and wherein the single mask defines areas of the scene occupied by an object to be identified.

28. The apparatus of claim 27, wherein the first, chrominance component includes a first color component and a second color component and the second chrominance component includes a third color component and a fourth color component, said at least one processor further for:

determining a difference between the first color component and the third color component to generate a first difference value; and

determining a difference between the second color component and the fourth color component to generate a second difference value.

29. The apparatus of claim 28, said at least one processor further for:

combining the first difference value and the second difference value to generate the chrominance mask.

30. The apparatus of claim 29, wherein the first difference value is weighted differently than the second difference value when combining the first difference value and the second difference value to generate the chrominance mask.

31. The apparatus of claim 29, said at least one processor further for:

combining the first difference value and the second difference value to generate a third difference value; and

thresholding the third difference value to generate the chrominance mask.

32. The apparatus of claim 31, wherein the first difference value is weighted differently than the second difference value when combining the first difference value and the second difference value to generate the third difference value.

33. The apparatus of claim 27, wherein the difference between the first and the second luminance components is thresholded to generate the luminance mask, and the difference between the first and the second chrominance components is thresholded to generate the chrominence mask.

34. An apparatus for differencing an image, said apparatus comprising:

a first obtainer for obtaining a first representation of a plurality of first pixels representing a scene at a first point in time, each of the first pixels having a first pixel parameter of a respective first value and a second pixel parameter of a respective second value;

a first determiner for determining a first difference value for each of the first pixels representing a difference between the first value of the first pixel parameter of each of the first pixels and a third value of the first pixel parameter of a corresponding one of a plurality of second pixels representing the scene at a second point in time;

a second determiner for determining a second difference value for each of the first pixels representing a difference between the second value of the second pixel parameter of each of the first pixels and a fourth value of the second pixel parameter of a corresponding one of the plurality of second pixels representing the scene at the second point in time;

a third determiner for determining a third difference value for each of the first pixels by combining the first difference value of a corresponding one of the plurality of first pixels and the second difference value of a corresponding one of the plurality of first pixels; and

a first identifier for identifying a plurality of third pixels, each of the third pixels being identified based upon a relation between the third difference value for a corresponding first pixel and a first threshold value; and

a first producer for producing a second representation of the plurality of third pixels to thereby represent a difference in the scene at the first point in time as compared to the scene at the second point in time.

35. The apparatus of claim 34, wherein the relation between the third difference value for a corresponding first pixel and the first threshold value is whether the third difference value for a corresponding first pixel exceeds the first threshold value.

36. The apparatus of claim 34, wherein the third difference value for each of the first pixels is determined by combining the first difference value of a corresponding one of the plurality of first pixels and the second difference value of a corresponding one of the plurality of first pixels such that the first difference value of a corresponding one of the plurality of first pixels is weighted differently than the second difference value of a corresponding one of the plurality of first pixels.

37. An apparatus for differencing an image, said apparatus comprising:

a first obtainer for obtaining a first representation of a plurality of first pixels representing a scene at a first point in time, each of the first pixels having a first pixel parameter of a respective first value and a second pixel parameter of a respective second value;

a first determiner for determining a first difference value for each of the first pixels representing a difference between the first value of the first pixel parameter of each of the first pixels and a third value of the first pixel parameter of a corresponding one of a plurality of second pixels representing the scene at a second point in time;

a second determiner for determining a second difference value for each of the first pixels representing a difference between the second value of the second pixel parameter of each of the first pixels and a fourth value of the second pixel parameter of a corresponding one of the plurality of second pixels representing the scene at the second point in time;

a first identifier for identifying a plurality of third pixels, each of the third pixels being identified based upon a relation between the first difference value for a corresponding first pixel and a first threshold value;

a second identifier for identifying a plurality of fourth pixels, each of the fourth pixels being identified based upon a relation between the second difference value for a corresponding first pixel and a second threshold value; and

a first producer for producing a second representation by combining the plurality of third pixels and the plurality of fourth pixels to thereby represent a difference in the scene at the first point in time as compared to the scene at the second point in time.

38. The apparatus of claim 37, wherein the relation between the first difference value for a corresponding first pixel and the first threshold value is whether the first difference value for a corresponding first pixel exceeds the first threshold value.

39. The apparatus of claim 37, wherein the relation between the second difference value for a corresponding first pixel and the second threshold value is whether the second difference value for a corresponding first pixel exceeds the second threshold value.

40. The apparatus of claim 37, wherein the first representation is a digital representation, and first obtainer obtains the first representation by imaging the scene.

41. The apparatus of claim 37, wherein the first pixel parameter is luminance and the second pixel parameter is a single color channel.

42. The apparatus of claim 37, wherein the first pixel parameter is a first color characteristic and the second pixel parameter is a second color characteristic.

43. The apparatus of claim 37, further comprising:

a second producer for producing a third representation of the plurality of third pixels; and

a third producer for producing a fourth representation of the plurality of fourth pixels;

wherein the second representation is produced by combining the third representation and the fourth representation.

44. The apparatus of claim 37, further comprising:

a third identifier for identifying a plurality of fifth pixels, each of the fifth pixels being identified by combining a corresponding one of the plurality of third pixels and a corresponding one of the plurality of fourth pixels;

wherein the second representation is produced from the plurality of fifth pixels.

45. The apparatus of claim 37, wherein each of the first pixels has a third pixel parameter of a respective fifth value, each of the second pixels has a respective sixth value of the third pixel parameter, and further comprising:

a third determiner for determining a third difference value for each of the first pixels representing a difference between the fifth value of the third pixel parameter of each of the first pixels and the sixth value of the third pixel parameter of a corresponding one of the plurality of second pixels;

a fourth determiner for determining a fourth difference value for each of the first pixels by combining the second difference value of a corresponding one of the plurality of first pixels and the third difference value of a corresponding one of the plurality of first pixels; and

a third identifier for identifying a plurality of fifth pixels, each of the fifth pixels being identified based upon a relation between the fourth difference value of a corresponding first pixel and a third threshold value;

wherein the second representation is produced by combining the plurality of third pixels and the plurality of fifth pixels.

46. The apparatus of claim 45, wherein the relation between the fourth difference value for a corresponding first pixel and the third threshold value is whether the fourth difference value for a corresponding first pixel exceeds the third threshold value.

47. The apparatus of claim 45, wherein the first pixel parameter is a first color characteristic, the second pixel parameter is a second color characteristic, and the third pixel parameter is a third color characteristic.

48. The apparatus of claim 45, wherein the first pixel parameter is luminance, the second pixel parameter is a relative amount of blue light, and the third pixel parameter is a relative amount of red light.

49. The apparatus of claim 45, further comprising:

a second producer for producing a third representation of the plurality of third pixels; and

a third producer for producing a fourth representation of the plurality of fifth pixels;

wherein the second representation is produced by combining the third representation and the fourth representation.

50. The apparatus of claim 45, further comprising:

a fourth identifier for identifying a plurality of sixth pixels each of the sixth pixels, being identified by combining a corresponding one of the plurality of third pixels and a corresponding one of the plurality of fifth pixels;

wherein the second representation is produced from the plurality of sixth pixels.

51. The apparatus of claim 45, wherein the fourth difference value for each of the first pixels is determined by combining the second difference value of a corresponding one of the plurality of first pixels and the third difference value of a corresponding one of the plurality of first pixels such that the second difference value of a corresponding one of the plurality of first pixels is weighted differently than the third difference value of a corresponding one of the plurality of first pixels.

52. The apparatus of claim 37, further comprising:

a second obtainer for obtaining a third representation of the plurality of second pixels to represent the scene at the second point in time.

53. An article of manufacture for differencing an image, said article of manufacture comprising:

a computer readable storage medium; and

computer programming stored on said storage medium;

wherein said stored computer programming is configured to be readable from said computer readable storage medium by a computer and thereby cause said computer to operate so as to;

obtain a first representation of a plurality of first pixels representing a scene at a first point in time, each of the first pixels having a first pixel parameter of a respective first value and a second pixel parameter of a respective second value;

determine a first difference value for each of the first pixels representing a difference between the first value of the first pixel parameter of each of the first pixels and a third value of the first pixel parameter of a corresponding one of a plurality of second pixels representing the scene at a second point in time;

determine a second difference value for each of the first pixels representing a difference between the second value of the second pixel parameter of each of the first pixels and a fourth value of the second pixel parameter of a corresponding one of the plurality of second pixels representing the scene at the second point in time;

determine a third difference value for each of the first pixels by combining the first difference value of a corresponding one of the plurality of first pixels and the second difference value of a corresponding one of the plurality of first pixels; and

identify a plurality of third pixels, each of the third pixels being identified based upon a relation between the third difference value for a corresponding first pixel and a first threshold value; and

produce a second representation of the plurality of third pixels to thereby represent a difference in the scene at the first point in time as compared to the scene at the second point in time.

54. The article of manufacture of claim 53, wherein the relation between the third difference value for a corresponding first pixel and the first threshold value is whether the third difference value for a corresponding first pixel exceeds the first threshold value.

55. The article of manufacture of claim 53, wherein the third difference value for each of the first pixels is determined by combining the first difference value of a corresponding one of the plurality of first pixels and the second difference value of a corresponding one of the plurality of first pixels such that the first difference value of a corresponding one of the plurality of first pixels is weighted differently than the second difference value of a corresponding one of the plurality of first pixels.

56. An article of manufacture for differencing an image, said article of manufacture comprising:

a computer readable storage medium; and

computer programming stored on said storage medium;

wherein said stored computer programming is configured to be readable from said computer readable storage medium by a computer and thereby cause said computer to operate so as to;

obtain a first representation of a plurality of first pixels representing a scene at a first point in time, each of the first pixels having a first pixel parameter of a respective first value and a second pixel parameter of a respective second value;

determine a first difference value for each of the first pixels representing a difference between the first value of the first pixel parameter of each of the first pixels and a third value of the first pixel parameter of a corresponding one of a plurality of second pixels representing the scene at a second point in time;

determine a second difference value for each of the first pixels representing a difference between the second value of the second pixel parameter of each of the first pixels and a fourth value of the second pixel parameter of a corresponding one of the plurality of second pixels representing the scene at the second point in time;

identify a plurality of third pixels, each of the third pixels being identified based upon a relation between the first difference value for a corresponding first pixel and a first threshold value;

identify a plurality of fourth pixels, each of the fourth pixels being identified based upon a relation between the second difference value for a corresponding first pixel and a second threshold value; and

produce a second representation by combining the plurality of third pixels and the plurality of fourth pixels to thereby represent a difference in the scene at the first point in time as compared to the scene at the second point in time.

57. The article of manufacture of claim 56, wherein the relation between the first difference value for a corresponding first pixel and the first threshold value is whether the first difference value for a corresponding first pixel exceeds the first threshold value.

58. The article of manufacture of claim 56, wherein the relation between the second difference value for a corresponding first pixel and the second threshold value is whether the second difference value for a corresponding first pixel exceeds the second threshold value.

59. The article of manufacture of claim 56, wherein the first representation is a digital representation, and further causing said computer to operate so as to:

obtain the first representation by imaging the scene.

60. The article of manufacture of claim 56, wherein the first pixel parameter is luminance and the second pixel parameter is a single color channel.

61. The article of manufacture of claim 56, wherein the first pixel parameter is a first color characteristic and the second pixel parameter is a second color characteristic.

62. The article of manufacture of claim 56, further causing said computer to operate so as to:

produce a third representation of the plurality of third pixels; and

produce a fourth representation of the plurality of fourth pixels;

wherein the second representation is produced by combining the third representation and the fourth representation.

63. The article of manufacture of claim 56, causing said computer to operate so as to:

identify a plurality of fifth pixels, each of the fifth pixels being identified by combining a corresponding one of the plurality of third pixels and a corresponding one of the plurality of fourth pixels;

wherein the second representation is produced from the plurality of fifth pixels.

64. The article of manufacture of claim 56, wherein each of the first pixels has a third pixel parameter of a respective fifth value, each of the second pixels has a respective sixth value of the third pixel parameter, and further causing said computer to operate so as to:

determine a third difference value for each of the first pixels representing a difference between the fifth value of the third pixel parameter of each of the first pixels and the sixth value of the third pixel parameter of a corresponding one of the plurality of second pixels;

determine a fourth difference value for each of the first pixels by combining the second difference value of a corresponding one of the plurality of first pixels and the third difference value of a corresponding one of the plurality of first pixels; and

identify a plurality of fifth pixels, each of the fifth pixels being identified based upon a relation between the fourth difference value of a corresponding first pixel and a third threshold value;

wherein the second representation is produced by combining the plurality of third pixels and the plurality of fifth pixels.

65. The article of manufacture of claim 64, wherein the relation between the fourth difference value for a corresponding first pixel and the third threshold value is whether the fourth difference value for a corresponding first pixel exceeds the third threshold value.

66. The article of manufacture of claim 64, wherein the first pixel parameter is a first color characteristic, the second pixel parameter is a second color characteristic, and the third pixel parameter is a third color characteristic.

67. The article of manufacture of claim 64, wherein the first pixel parameter is luminance, the second pixel parameter is a relative amount of blue light, and the third pixel parameter is a relative amount of red light.

68. The article of manufacture of claim 64, further causing said computer to operate so as to:

produce a third representation of the plurality of third pixels; and

produce a fourth representation of the plurality of fifth pixels;

wherein the second representation is produced by combining the third representation and the fourth representation.

69. The article of manufacture of claim 64, further causing said computer to operate so as to:

identify a plurality of sixth pixels, each of the sixth pixels being identified by combining a corresponding one of the plurality of third pixels and a corresponding one of the plurality of fifth pixels;

wherein the second representation is produced from the plurality of sixth pixels.

70. The article of manufacture of claim 64, wherein the fourth difference value for each of the first pixels is determined by combining the second difference value of a corresponding one of the plurality of first pixels and the third difference value of a corresponding one of the plurality of first pixels such that the second difference value of a corresponding one of the plurality of first pixels is weighted differently than the third difference value of a corresponding one of the plurality of first pixels.

71. The article of manufacture of claim 56, further causing said computer to operate so as to:

obtain a third representation of the plurality of second pixels to represent the scene at the second point in time.