Video based color sensing device for a printing press control system

• US 5,767,980 A
• Filed: 06/20/1995
• Issued: 06/16/1998
• Est. Priority Date: 06/20/1995
• Status: Expired due to Term

• Current Assignee: Shanghai Electric (Group) Corporation (City of Shanghai)
• Original Assignee: GOSS Graphic Systems(China) Company Limited (City of Shanghai)
• Inventors: Wang, Xin xin, Nemeth, Robert
• Primary Examiner(s): FRAHM, ERIC S
• Application Number:
  US08/493,184
• Time in Patent Office: 1,092 Days
• Field of Search: 358/298, 358/406, 358/500, 358/501, 358/504, 358/505, 358/509-514, 358/518-523, 358/530-538, 382/162, 382/167, 382/312, 382/318, 382/319
• US Class Current: 358/475
• CPC Class Codes: B41F 33/0036 Devices for scanning or checking the printed matter for quality control

Abstract

A color sensing device of a printing press control system, having a plurality of lamp fixtures (100 and 102) for providing light in the visible region and the near infrared region of the spectrum to illuminate a viewing area (104), a camera assembly (108), the camera assembly having multiple channels to capture images in the visible region and the near infrared region, and at least one lens for generating the images, a calibration target (108) with a uniform light reflectance, a device for adjusting the distribution of the light so that image captured from said calibration target in each channel of the camera assembly is as even as possible, a device for applying a position related compensation process in order to obtain an image which corresponds to a position-invariant viewing condition, and a device for applying a camera value related compensation process in order to obtain an image under a standard viewing condition.

Claims

1. A device to provide a substantially uniform lighting condition as perceived by a color sensing device for a control system in a printing press, comprising:

a first lamp for generating light in at least a visible region of a light spectrum;

a second lamp for generating light in only an infrared region of the light spectrum;

a calibration target; and

means for capturing images in the visible and the infrared regions;

wherein the light output by the first lamp is adjustable to reduce unevenness in a first image captured by the capturing means in the visible region, and the light output by the second lamp is adjustable to reduce unevenness in a second image captured by the capturing means in the infrared region to thereby develop a substantially uniform lighting condition as perceived by a color sensing device.

2. A device as defined in claim 1 further comprising position compensation means for applying a position related compensation process to images captured by the capturing means to produce a position-invariant viewing condition.

3. A device as defined in claim 2 wherein the position compensation means generates a compensation image from at least one image captured by the capturing means from the calibration target, and the position compensation means applies the compensation image to subsequent images captured by the capturing means to provide the position-invariant viewing condition.

4. A device as defined in claim 2 wherein the position compensation means comprises a central processing unit.

5. A device as defined in claim 1 wherein the capturing means comprises a camera, and further comprising camera value compensation means for applying at least one camera value related compensation process to images captured by the capturing means to produce a time-invariant viewing condition.

6. A device as defined in claim 5 wherein the camera value related compensation means comprises a central processing unit.

7. A device as defined in claim 5 wherein the at least one camera value related compensation process is implemented through a lookup table.

8. A device as defined in claim 5 wherein the at least one camera value related compensation process is developed from captured images of a gray scale.

9. A device as defined in claim 1 wherein the capturing means comprises a camera assembly having four channels.

10. A device as defined in claim 9 wherein the four channels comprise red, green, blue, and infrared channels.

11. A device as defined in claim 10 wherein the camera assembly comprises a color camera and a monochrome camera, the color camera providing the red, green and blue channels and the monochrome camera providing the infrared channel, the color camera having a lens and the monochrome camera having a lens.

12. A device as defined in claim 10 wherein the camera assembly comprises an integrated four channel camera having a single lens.

13. A device as defined in claim 9 wherein each channel of the camera assembly comprises a Charge Coupled Device image sensor.

14. A device as defined in claim 1 wherein the capturing means has an associated optical axis, the optical axis being substantially perpendicular to a surface of a viewing area.

15. A device as defined in claim 14 wherein the first lamp is positioned to emit light at an approximately 45 degree angle to the optical axis.

16. A device as defined in claim 14 wherein the second lamp is positioned to emit light at an approximately 45 degree angle to the optical axis.

17. A device as defined in claim 1 wherein the calibration target comprises a blank sheet of paper.

18. A device as defined in claim 1 wherein the calibration target includes a painted working surface having a glossiness and lightness which is substantially similar to glossiness and lightness of a blank sheet of paper.

19. A device as defined in claim 1 wherein the calibration target has a substantially flat spectral reflectance curve at least in a wavelength range from approximately 400 nm to 1000 nm.

20. A device as defined in claim 1 wherein the light output by the first lamp is adjusted via a mesh screen.

21. A device as defined in claim 1 wherein the light output by the first lamp is adjusted via a neutral density filter.

22. A device as defined in claim 1 wherein the light output by the first lamp is adjusted by changing an orientation or position of the first lamp.

23. A device as defined in claim 1 wherein the output of the second lamp is adjusted via a mesh screen.

24. A device as defined in claim 1 wherein the output of the second lamp is adjusted via a neutral density filter.

25. A device as defined in claim 1 wherein the output of the second lamp is adjusted by changing an orientation or position of the second lamp.

26. A device as defined in claim 1 further comprising a display for viewing the images obtained by the capturing means and a programmable display lookup table for making image intensity variation appear more prominent on the display.

27. A device as defined in claim 1 wherein the first image is a green image.

28. A device as defined in claim 1 wherein a third image and a fourth image captured by the capturing means in the visible region are checked for unevenness to detect a need for correcting spectral output of the first lamp, and wherein the first image is a green image, the third image is a red image, and the fourth image is a blue image.

29. A device as defined in claim 1 wherein the first lamp comprises a set of lamps.

30. A device as defined in claim 1 wherein the second lamp comprises a set of lamps.

31. A device as defined in claim 1 wherein the first lamp generates light in the visible and the infrared regions of the spectrum.

32. A device to provide a substantially uniform lighting condition as perceived by a color sensing device for a control system in a printing press, comprising:

a first lamp for generating light in only a visible region of a light spectrum;

a second lamp for generating light in at least an infrared region of the light spectrum;

a calibration target; and

means for capturing images in the visible and the infrared regions;

wherein the light output by the first lamp is adjustable to reduce unevenness in a first image captured by the capturing means in the visible region, and the light output by the second lamp is adjustable to reduce unevenness in a second image captured by the capturing means in the infrared region to thereby develop a substantially uniform lighting condition as perceived by a color sensing device.

33. A device as defined in claim 32 further comprising position compensation means for applying a position related compensation process to images captured by the capturing means to produce a position-invariant viewing condition.

34. A device as defined in claim 33 wherein the position compensation means generates a compensation image from at least one image captured by the capturing means from the calibration target, and the position compensation means applies the compensation image to subsequent images captured by the capturing means to provide the position-invariant viewing condition.

35. A device as defined in claim 33 wherein the position compensation means comprises a central processing unit.

36. A device as defined in claim 32 wherein the capturing means comprises a camera, and further comprising camera value related compensation means for applying at least one camera value related compensation process to images captured by the capturing means to produce a time-invariant viewing condition.

37. A device as defined in claim 60 wherein the camera value related compensation means comprises a central processing unit.

38. A device as defined in claim 36 wherein the at least one camera value related compensation process is implemented through a lookup table.

39. A device as defined in claim 36 wherein the at least one camera value related compensation process is developed from captured images of a gray scale.

40. A device as defined in claim 32 wherein the capturing means comprises a camera assembly having four channels.

41. A device as defined in claim 40 wherein the four channels comprise red, green, blue, and infrared channels.

42. A device as defined in claim 41 wherein the camera assembly comprises a color camera and a monochrome camera, the color camera providing the red, green and blue channels and the monochrome camera providing the infrared channel, the color camera having a lens and the monochrome camera having a lens.

43. A device as defined in claim 41 wherein the camera assembly comprises an integrated four channel camera having a single lens.

44. A device as defined in claim 40 wherein each channel of the camera assembly comprises a Charge Coupled Device image sensor.

45. A device as defined in claim 32 wherein the capturing means has an associated optical axis, the optical axis being substantially perpendicular to a surface of a viewing area.

46. A device as defined in claim 45 wherein the first lamp is positioned to emit light at an approximately 45 degree angle to the optical axis.

47. A device as defined in claim 45 wherein the second lamp is positioned to emit light at an approximately 45 degree angle to the optical axis.

48. A device as defined in claim 32 wherein the calibration target comprises a blank sheet of paper.

49. A device as defined in claim 32 wherein the calibration target includes a painted working surface having a glossiness and lightness which is substantially similar to glossiness and lightness of a blank sheet of paper.

50. A device as defined in claim 32 wherein the calibration target has a substantially flat spectral reflectance curve at least in a wavelength range from approximately 400 nm to 1000 nm.

51. A device as defined in claim 32 wherein the light output by the second lamp is adjusted via a mesh screen.

52. A device as defined in claim 32 wherein the light output by the second lamp is adjusted via a neutral density filter.

53. A device as defined in claim 32 wherein the light output by the first lamp is adjusted by changing an orientation or position of the first lamp.

54. A device as defined in claim 32 wherein the output of the second lamp is adjusted via a mesh screen.

55. A device as defined in claim 32 wherein the output of the second lamp is adjusted via a neutral density filter.

56. A device as defined in claim 32 wherein the output of the second lamp is adjusted by changing an orientation or position of the second lamp.

57. A device as defined in claim 32 further comprising a display for viewing the images obtained by the capturing means and a programmable display lookup table for making image intensity variation appear more prominent on the display.

58. A device as defined in claim 32 wherein the first image is a green image.

59. A device as defined in claim 32 wherein a third image and a fourth image captured by the capturing means in the visible region are checked for unevenness to detect a need for correcting spectral output of the second lamp, and wherein the first image is a green image, the third image is a red image, and the fourth image is a blue image.

60. A device as defined in claim 32 wherein the first lamp comprises a set of lamps.

61. A device as defined in claim 32 wherein the second lamp comprises a set of lamps.

62. A device as defined in claim 32 wherein the second lamp generates light in the visible and the infrared regions of the spectrum.

63. A method of providing a substantially uniform lighting condition as perceived by a color sensing device for a control system in a printing press, comprising the steps of:

providing first and second lamps, the first lamp producing light in at least a visible region of a light spectrum and the second lamp producing light in only an infrared region of the light spectrum;

providing a camera for viewing images on at least two channels, at least one of the channels being in the infrared region and at least one of the channels being in the visible region;

providing a calibration target;

viewing a first image of the calibration target in a visible region of the light spectrum with the camera;

reducing unevenness in the first image by adjusting the first lamp;

viewing a second image of the calibration target in the infrared region of the light spectrum with the camera; and

reducing unevenness in the second image by adjusting the second lamp.

64. A method as defined in claim 63 further comprising the step of viewing third and fourth images of the calibration target in the visible region of the camera for unevenness to check the spectral output of the first lamp, wherein the first image is a green image, the third image is a red image, and the fourth image is a blue image.

65. A method as defined in claim 63 further comprising the steps of:

capturing multiple images of the calibration target on each channel of the camera;

developing an averaged image for each of the channels by averaging corresponding pixels in the multiple images captured on each channel;

identifying a highest pixel value in each of the averaged images;

developing an intermediate compensation image for each channel by dividing the highest pixel value captured for each channel by every pixel in the averaged image of the corresponding channel;

capturing a channel image to be processed on each channel of the camera; and

multiplying pixels in each of the channel images to be processed with corresponding pixels in the intermediate compensation image for the corresponding channel.

66. A method as defined in claim 63 further comprising the steps of:

providing a gray scale calibration target having a plurality of steps with different darkness characteristics;

measuring light reflectance for the plurality of steps on each channel of the camera;

calculating an average light reflectance over the bandwidth of each camera channel for each step in the plurality;

determining desired camera values for the plurality of steps in the gray scale calibration target;

adjusting the camera such that a measured camera value obtained from a lightest step on the gray scale calibration target is substantially equal to the desired camera value for the lightest step on the gray scale calibration target; and

mapping the measured camera values to the desired camera values for the plurality of steps in the gray scale calibration target for each channel of the camera.

67. A method of providing a substantially uniform lighting condition as perceived by a color sensing device for a control system in a printing press, comprising the steps of:

providing first and second lamps, the first lamp producing light in only a visible region of a light spectrum, the second lamp producing light in at least an infrared region of the light spectrum;

providing a camera for viewing images on at least two channels, at least one of the channels being in the infrared region and at least one of the channels being in the visible region;

providing a calibration target;

viewing a first image of the calibration target in a visible region of the light spectrum with the camera;

reducing unevenness in the first image by adjusting the first lamp;

viewing a second image of the calibration target in the infrared region of the light spectrum with the camera; and

reducing unevenness in the second image by adjusting the second lamp.

68. A method as defined in claim 67 further comprising the step of viewing third and fourth images of the calibration target in the visible region of the camera for unevenness to check the spectral output of the second lamp, wherein the first image is a green image, the third image is a red image, and the fourth image is a blue image.

69. A method as defined in claim 67 further comprising the steps of:

capturing multiple images of the calibration target on each channel of the camera;

developing an averaged image for each of the channels by averaging corresponding pixels in the multiple images captured on each channel;

identifying a highest pixel value in each of the averaged images;

developing an intermediate compensation image for each channel by dividing the highest pixel value captured on each channel by every pixel in the averaged image of the corresponding channel;

capturing a channel image to be processed on each channel of the camera; and

multiplying pixels in each of the channel images to be processed with corresponding pixels in the intermediate compensation image for the corresponding channel.

70. A method as defined in claim 67 further comprising the steps of:

providing a gray scale calibration target having a plurality of steps with different darkness characteristics;

measuring light reflectance for the plurality of steps on each channel of the camera;

calculating an average light reflectance over the bandwidth of each camera channel for each step in the plurality;

determining desired camera values for the plurality of steps in the gray scale calibration target;

adjusting the camera such that a measured camera value obtained from a lightest step on the gray scale calibration target is substantially equal to the desired camera value for the lightest step on the gray scale calibration target; and

mapping the measured camera values to the desired camera values for the plurality of steps in the gray scale calibration target for each channel of the camera.