Imaging system with a lens having increased light collection efficiency and a deblurring equalizer

Abstract

In one form, an imaging system comprises an imager that forms an image of an object in a field of view, a rotationally symmetric lens assembly disposed between the imager and the object, and an equalizer. The rotationally symmetric lens assembly provides increased collection efficiency for a given depth of field, whereby the rotationally symmetric lens assembly causes aberration, compared to a well-focused lens. The rotationally symmetric lens assembly comprises a front negative lens, a rear positive lens, and an aperture positioned between the front and rear lenses. The equalizer, which is connected to the imager, receives image data and at least partially compensates for the aberration caused by the rotationally symmetric lens assembly.

1. An imaging system comprising:
 an imager that forms an electronic image of an object in a field of view; 
 a rotationally symmetric lens assembly disposed between the imager and the object, the lens assembly providing increased collection efficiency for a desired depth of field, whereby the lens assembly causes aberration, compared to a well-focused lens; and 
 a signal processor connected to the imager, wherein the signal processor receives image data and generates a virtual scan line signal comprising samples taken from a line across the image, wherein the signal processor comprises:
 a non-uniform scaler that receives the virtual scan line signal and scales samples in the virtual scan line signal to generate a non-uniformly scaled virtual scan line signal; and 
 an equalizer that receives the non-uniformly scaled virtual scan line signal and equalizes the non-uniformly scaled virtual scan line signal so as to at least partially compensate for the aberration caused by the lens assembly. 
 
 
     
     
       2. An imaging system according to  claim 1 , wherein the rotationally symmetric lens assembly comprises a generalized axicon lens. 
     
     
       3. An imaging system according to  claim 1 , wherein the rotationally symmetric lens assembly comprises:
 a front negative lens; 
 a rear positive lens; and 
 an aperture positioned between the front and rear lenses. 
 
     
     
       4. An imaging system according to  claim 3 , wherein the front negative lens is a biconcave lens. 
     
     
       5. An imaging system according to  claim 3 , wherein the front negative lens is a plano-concave lens. 
     
     
       6. An imaging system according to  claim 3 , wherein the rear positive lens is a biconvex lens. 
     
     
       7. An imaging system according to  claim 3 , wherein the rear positive lens is a plano-convex lens. 
     
     
       8. An imaging system according to  claim 1 , wherein the equalizer is one-dimensional, whereby the imaging system is largely invariant to angular orientation of the virtual scan line across the image from which the samples are taken for the virtual scan line signal. 
     
     
       9. An imaging system according to  claim 1 , wherein the equalizer has a transfer function that is approximately an inverse of a modulation transfer function of the rotationally symmetric lens assembly. 
     
     
       10. An imaging system according to  claim 1 , wherein the rotationally symmetric lens assembly has an aperture size greater than a well-focused lens having a similar depth of field as the rotationally symmetric lens assembly, whereby the imaging system generates well-formed images of the object as the object moves across the field of view at a higher speed than if a well-focused lens were utilized. 
     
     
       11. An imaging system comprising:
 an imager that forms an electronic image of an object in a field of view; 
 a rotationally symmetric lens assembly disposed between the imager and the object, the rotationally symmetric lens assembly providing increased collection efficiency for a desired depth of field, whereby the rotationally symmetric lens assembly causes aberration, compared to a well-focused lens, the rotationally symmetric lens assembly comprising:
 a front negative lens; 
 a rear positive lens; and 
 an aperture positioned between the front and rear lenses; and 
 an equalizer connected to the imager, wherein the equalizer receives image data and at least partially compensates for the aberration caused by the rotationally symmetric lens assembly. 
 
 
     
     
       12. An imaging system according to  claim 11 , wherein the rotationally symmetric lens assembly is a generalized axicon. 
     
     
       13. An imaging system according to  claim 11 , wherein the equalizer is one-dimensional. 
     
     
       14. An imaging system according to  claim 13 , wherein the input to the equalizer is a virtual scan line signal comprising samples taken from a line across the image. 
     
     
       15. An imaging system according to  claim 11 , wherein the front negative lens is a biconcave lens. 
     
     
       16. An imaging system according to  claim 11 , wherein the front negative lens is a piano-concave plano-concave lens. 
     
     
       17. An imaging system according to  claim 11 , wherein the rear positive lens is a biconvex lens. 
     
     
       18. An imaging system according to  claim 11 , wherein the rear positive lens is a plano-convex lens. 
     
     
       19. An imaging system according to  claim 11 , wherein the equalizer has a transfer function that is approximately an inverse of a modulation transfer function of the rotationally symmetric lens assembly. 
     
     
       20. An imaging system according to  claim 11 , wherein the rotationally symmetric lens assembly has an aperture size greater than a well-focused lens having a similar depth of field as the rotationally symmetric lens assembly, whereby the imaging system generates well-formed images of the object as the object moves across the field of view at a higher speed than if a well-focused lens were utilized. 
     
     
       21. An imaging system according to  claim 11 , wherein the image comprises a plurality of pixels, the imaging system further comprising:
 a plurality of pixel-specific gain elements that scale pixel values individually so as to compensate for nonuniformity in the formation of the intensity of the pixel values. 
 
     
     
       22. A method comprising:
 passing light from an object through a negative lens; 
 blocking a light from a periphery region of the negative lens while passing light from a central region of the negative lens; 
 passing the light from the central region of the negative lens through a positive lens; 
 forming an image of the object based on the light from the positive lens; 
 generating a virtual scan line signal comprising samples taken from one or more lines across the image at one or more arbitrary angles; 
 scaling the samples of the virtual scan line signal by non-uniform amounts; and 
 equalizing the non-uniformly scaled virtual scan line signal so as to at least partially compensate for blurriness caused by one or more of the lenses. 
 
     
     
       23. An imaging system according to claim 1, wherein the virtual scan line signal comprises an ordered set of pixels that is taken from a line that extends across the image at a slanted angle, and wherein the non-uniform scaler scales pixels within the ordered set of pixels to generate a non-uniformly scaled virtual scan line signal. 
     
     
       24. An imaging system according to claim 23, wherein the imager comprises a two-dimensional array of pixels such that the pixels are arranged in lines that extend in two directions, and wherein the line from which the ordered set of pixels is taken extends across the image at a non-zero angle relative to the lines of pixels of the two-dimensional array. 
     
     
       25. An imaging system according to claim 1, wherein the signal processor generates multiple virtual scan line signals comprising samples taken from multiple lines that extend across the image at multiple angles, at least two of which are different from each other. 
     
     
       26. An imaging system according to claim 25, wherein the imager comprises a two-dimensional array of pixels such that the pixels are arranged in lines that extend in two directions, and wherein the multiple lines from which samples are taken extend across the image at multiple angles, at least two of which are different from each other, relative to the lines of pixels of the two-dimensional array. 
     
     
       27. A system for reading an optical code, the system comprising:
 an imager that forms an electronic image of an object bearing an optical code in a field of view;   a rotationally symmetric lens assembly disposed between the imager and the object, the lens assembly providing increased collection efficiency for a desired depth of field, whereby the lens assembly causes aberration, compared to a well-focused lens; and   a signal processor connected to the imager, wherein the signal processor receives image data and generates one or more virtual scan line signals comprising samples taken from one or more lines across the image.   
     
     
       28. A system according to claim 27, wherein the signal processor comprises:
 an equalizer that receives a virtual scan line signal and equalizes the received virtual scan line signal so as to at least partially compensate for the aberration caused by the lens assembly.   
     
     
       29. A system according to claim 28, wherein the signal processor further comprises:
 a non-uniform scaler that receives a virtual scan line signal and scales samples in the virtual scan line signal to generate a non-uniformly scaled virtual scan line signal for input to the equalizer.   
     
     
       30. A system according to claim 28, wherein the equalizer is one-dimensional, whereby the system is largely invariant to angular orientation of the line across the image from which the samples are taken for the virtual scan line signal. 
     
     
       31. A system according to claim 28, wherein the equalizer has a transfer function that is approximately an inverse of a modulation transfer function of the rotationally symmetric lens assembly. 
     
     
       32. A system according to claim 27, wherein the rotationally symmetric lens assembly comprises a generalized axicon lens. 
     
     
       33. A system according to claim 27, wherein the rotationally symmetric lens assembly comprises:
 a front negative lens;   a rear positive lens; and   an aperture positioned between the front and rear lenses.   
     
     
       34. A system according to claim 33, wherein the front negative lens is a biconcave lens. 
     
     
       35. A system according to claim 33, wherein the front negative lens is a plano-concave lens. 
     
     
       36. A system according to claim 33, wherein the rear positive lens is a biconvex lens. 
     
     
       37. A system according to claim 33, wherein the rear positive lens is a plano-convex lens. 
     
     
       38. A system according to claim 27, wherein the rotationally symmetric lens assembly has an aperture size greater than a well-focused lens having a similar depth of field as the rotationally symmetric lens assembly, whereby the system generates well-formed images of the object as the object moves across the field of view at a higher speed than if a well-focused lens were utilized. 
     
     
       39. A system according to claim 27, wherein the optical code is a bar code. 
     
     
       40. A system according to claim 27, wherein each of the one or more virtual scan line signals comprises an ordered set of pixels that is taken from a line that extends across the image at a slanted angle. 
     
     
       41. A system according to claim 40, wherein the imager comprises a two-dimensional array of pixels such that the pixels are arranged in lines that extend in two directions, and wherein the line from which the ordered set of pixels is taken extends across the image at a non-zero angle relative to the lines of pixels of the two-dimensional array. 
     
     
       42. A system according to claim 27, wherein the signal processor generates multiple virtual scan line signals comprising samples taken from multiple lines that extend across the image at multiple angles, at least two of which are different from each other. 
     
     
       43. A system according to claim 42, wherein the imager comprises a two-dimensional array of pixels such that the pixels are arranged in lines that extend in two directions, and wherein the multiple lines from which samples are taken extend across the image at multiple angles, at least two of which are different from each other, relative to the lines of pixels of the two-dimensional array. 
     
     
       44. An imaging system comprising:
 an imager that forms an electronic image of an optical code on an object in a field of view;   a rotationally symmetric lens assembly disposed between the imager and the object, the rotationally symmetric lens assembly providing increased collection efficiency for a desired depth of field, whereby the rotationally symmetric lens assembly causes aberration, compared to a well-focused lens, the rotationally symmetric lens assembly comprising:
 a front negative lens; 
 a rear positive lens; and 
 an aperture positioned between the front and rear lenses; and 
   a signal processor connected to the imager and configured to generate one or more virtual scan line signals comprising samples taken from one or more lines across the image.   
     
     
       45. An imaging system according to claim 44, wherein the signal processor comprises an equalizer connected to the imager, wherein the equalizer receives image data and at least partially compensates for the aberration caused by the rotationally symmetric lens assembly. 
     
     
       46. An imaging system according to claim 45, wherein the equalizer is one-dimensional. 
     
     
       47. An imaging system according to claim 45, wherein the input to the equalizer is a virtual scan line signal comprising samples taken from a line across the image. 
     
     
       48. An imaging system according to claim 45, wherein the equalizer has a transfer function that is approximately an inverse of a modulation transfer function of the rotationally symmetric lens assembly. 
     
     
       49. An imaging system according to claim 44, wherein the rotationally symmetric lens assembly is a generalized axicon. 
     
     
       50. An imaging system according to claim 44, wherein the front negative lens is a biconcave lens. 
     
     
       51. An imaging system according to claim 44, wherein the front negative lens is a plano-concave lens. 
     
     
       52. An imaging system according to claim 44, wherein the rear positive lens is a biconvex lens. 
     
     
       53. An imaging system according to claim 44, wherein the rear positive lens is a plano-convex lens. 
     
     
       54. An imaging system according to claim 44, wherein the rotationally symmetric lens assembly has an aperture size greater than a well-focused lens having a similar depth of field as the rotationally symmetric lens assembly, whereby the imaging system generates well-formed images of the object as the object moves across the field of view at a higher speed than if a well-focused lens were utilized. 
     
     
       55. An imaging system according to claim 44, wherein the image comprises a plurality of pixels, the imaging system further comprising:
 a plurality of pixel-specific gain elements that scale pixel values individually so as to compensate for nonuniformity in the formation of the intensity of the pixel values.   
     
     
       56. An imaging system according to claim 44, wherein the optical code is a bar code. 
     
     
       57. A method comprising:
 passing light from an optical code on an object through a negative lens;   blocking a light from a periphery region of the negative lens while passing light from a central region of the negative lens;   passing the light from the central region of the negative lens through a positive lens;   forming an image of the optical code based on the light from the positive lens; and   generating at least one virtual scan line signal comprising samples taken from one or more lines across the image.   
     
     
       58. A method according to claim 57, further comprising:
 scaling the samples of the virtual scan line signal by non-uniform amounts; and   equalizing the non-uniformly scaled virtual scan line signal so as to at least partially compensate for blurriness caused by one or more of the lenses.   
     
     
       59. A method according to claim 57, further comprising:
 equalizing the virtual scan line signal so as to at least partially compensate for blurriness caused by one or more of the lenses.   
     
     
       60. A method according to claim 57, wherein the one or more lines across the image include lines at different angles. 
     
     
       61. A method according to claim 57, wherein the optical code is a bar code. 
     
     
       62. A method according to claim 57, wherein the at least one virtual scan line signal comprises an ordered set of pixels taken from a line across the image at a slanted angle. 
     
     
       63. A method according to claim 57, further comprising generating multiple virtual scan line signals comprising samples taken from multiple lines across the image at multiple angles, wherein at least two of the angles are different from each other.