Measuring the quality of images

• US 4,053,934 A
• Filed: 05/12/1975
• Issued: 10/11/1977
• Est. Priority Date: 12/29/1972
• Status: Expired due to Term

• Current Assignee: Philipp G. Kornreich, Stephen T. Kowel
• Original Assignee: Philipp G. Kornreich, Stephen T. Kowel
• Inventors: Kornreich, Philipp G., Kowel, Stephen T.
• Primary Examiner(s): Martin, John C.
• Application Number:
  US05/576,433
• Time in Patent Office: 883 Days
• Field of Search: 03B/13/20, 178/7.1, 178/DIG. 29, 250/201, 250/234, 250/204, 250/567, 350/41, 350/46, 350/161, 352/140, 353/101, 354/25, 356/4, 356/71, 310/8.1, 310/8.3, 355/56, 358/213, 358/227, 340/146.3 P
• US Class Current: 348/198
• CPC Class Codes: G02B 27/40 Optical focusing aids
• CPC Class Codes: G02B 7/365 by analysis of the spatial frequency components of the image
• CPC Class Codes: G08B 13/1961 Movement detection not involving frame subtraction, e.g. motion detection on the basis of luminance changes in the image
• CPC Class Codes: G08B 13/19626 optical details, e.g. lenses, mirrors or multiple lenses
• CPC Class Codes: G08B 13/19634 Electrical details of the system, e.g. component blocks for carrying out specific functions

Abstract

Method and apparatus for measuring the quality and sharpness of images and for using the measurement results to control parameters such as camera and projector focusing, range finding, optical system modifications and the like. In one embodiment, an image is formed on a medium which has an electrical property that varies predictably with the sharpness of an image incident on it. The property is measured and the derived electrical signal controls automatic focusing of objective and projection lenses, range finder settings, and the like. The invention relies on the discovery of an interaction between images, strain waves and electrical properties in certain devices which allows deriving an electrical signal whose magnitude corresponds to high spatial frequency Fourier components of the image. In addition to other useful characteristics, the electrical signal is at a maximum when the overall sharpness of the image is high and drops off significantly as the image becomes blurred. Alternately, high frequency components of the spatial Fourier transform of images are found by other means, e.g., optically, and the magnitude of these components is used as an indication of the sharpness of the images, and of other parameters of optical systems.

Claims

1. Apparatus for detecting the sharpness of an image comprising:

a medium having a measurable property which varies as a function of the intensity pattern of an image formed thereon and as a function of strain disturbances in the medium;

means for forming a selected image on the medium;

means for causing a selected strain disturbance in the medium which propagates along the image formed on the medium; and

means for measuring said property while the image is formed on the medium and while the selected strain disturbance is present therein and for deriving thereby a signal which is a Fourier transform representation of an aspect of the entire image and which represents the sharpness of the image formed on the medium but is substantially independent of the average intensity of the image formed on the medium and means for utilizing said signal for control purposes.

2. Apparatus as in claim 1 wherein said selected strain disturbance is periodic in time and space.

3. Apparatus as in claim 2 wherein said selected strain disturbance is a strain wave of a selected spatial frequency.

4. Apparatus as in claim 3 wherein said selected spatial frequency corresponds to a spatial wavelength which is longer than twice the maximum desired measurable resolution of the selected image but is substantially shorter than the size of the selected image.

5. Apparatus as in claim 3 wherein the selected spatial frequency corresponds to spatial wavelength of the order of one millimeter.

6. Apparatus as in claim 1 wherein said property varies as a function of the image sharpness along only a single selected dimension of the image.

7. Apparatus as in claim 1 wherein said property of the medium varies as a function of the image sharpness along at least two dimensions of the image.

8. Apparatus as in claim 1 wherein:

said selected strain disturbance in the medium is a selected strain wave propagating through the medium;

the signal derived by measuring said property is an electrical signal and the steady state magnitude thereof represents said sharpness; and

said magnitude corresponds to a Fourier transform representation of the intensity pattern along at least one dimension of the image formed on the medium for the spatial frequency of the selected strain wave.

9. Apparatus as in claim 1 wherein:

said medium comprises a substrate of a material capable of undergoing strain disturbances and a film acoustically coupled to a surface of the substrate to undergo strain disturbances therewith and having an electrical property which varies as a function of the intensity pattern of an image formed thereon and as a function of strain disturbances in the film, and a pair of electrically conductive contacts disposed in electrical contact with the film and spaced from each other by a strip of film;

said means for forming an image on the medium forms said image on the strip of film; and

said measuring means includes an electrical bias source connected to the two contacts to establish a potential difference therebetween across the film strip and means for detecting the electrical conductivity of the film strip to derive an electrical signal representing the sharpness of the entire image formed on the film strip along the length of the strip.

10. Apparatus as in claim 9 wherein the means for causing a strain disturbance propagates a surface strain wave along the surface of the substrate facing the film.

11. Apparatus as in claim 1 wherein:

the medium comprises a substrate of a material capable of undergoing strain disturbances and a film acoustically coupled to a surface of the substrate to undergo strain disturbances therewith and having an electrical property which varies as a function of the intensity pattern of an image formed on the film and as a function of strain disturbances in the film;

the means for forming an image on the medium forms the image on at least a portion of the film; and

the measuring means measures said electrical property of the film to derive an electrical signal corresponding to a selected spatial wavelength of the strain disturbance and representing the resolution of the image formed on the film, and comprises an interdigitated plurality of first and second electrically conductive contacts disposed in electrical contact with the film, with the first contacts electrically connected to each other and the second contacts electrically connected to each other, but with the first and second contacts spaced from each other long the film, and means for establishing a selected bias between the first and second contacts, said electrical signal corresponding to the conductivity of the film between the first and second contacts for said selected spatial wavelength.

12. Apparatus as in claim 11 wherein the measuring means measures the AC conductivity of the film between the contacts for the wavelength of the selected strain disturbance.

13. Apparatus as in claim 12 wherein the magnitude maximum of the measured electrical signal corresponds to maximum sharpness of the image when the image sharpness varies through a selected range.

14. Apparatus as in claim 1 wherein the medium comprises:

a substrate of a material capable of undergoing strain disturbances, a first electrically conductive film disposed on a surface of the substrate, a selected electrically isolating film disposed on the first conductive film and in acoustic coupling with the substrate, and a second electrically conductive film disposed on the side of the isolating film facing away from the substrate, at least one of said conductive films being substantially transparent to said image;

the image forming means forms the image on the isolating film; and

the measuring means comprises means for measuring the conductivity between the two electrically conductive films, across the isolating film, to thereby derive an electrical signal having a defined parameter whose value represents the sharpness of the entire image formed on the isolating film sandwiched between the conductive films.

15. Apparatus as in claim 1 including a photographic camera having an image receiving surface, an objective lens for projecting an image on the image receiving surface, wherein the means for forming said selected image comprises means for forming on the medium an image whose sharpness is functionally related to that of the image projected by the objective lens on the image receiving surface, thereby deriving a signal which is functionally related to the degree of sharpness of the image projected on said image receiving surface.

16. Apparatus as in claim 15 including means responsive to said signal for changing the focusing of said objective lens in accordance with said signal.

17. Apparatus as in claim 1 including a projector having an image carrier, a projection lens, and a light source for projecting the image from the carrier onto a screen plane, wherein the means for forming said selected image comprises means forming on said medium an image whose sharpness is functionally related to that of the image projected on the screen plane, thereby deriving a signal functionally related to the degree of sharpness of the image projected on the screen plane.

18. Apparatus as in claim 17 including means responsive to said signal for changing the focusing of said projection lens in accordance with said signal.

19. Apparatus as in claim 1 wherein said strain disturbance is a strain wave progagating through the portion of the medium on which the image is formed and having a spatial frequency which repeatedly scans through a defined frequency range.

20. Apparatus as in claim 19 wherein said strain wave comprises two strain waves propagating through the medium along two dimensions of the image formed thereon.

21. Apparatus as in claim 1 wherein said strain disturbance comprises two strain waves propagating through the medium along two dimensions of the image formed thereon.

22. Apparatus as in claim 21 wherein the spatial frequency of each strain wave repeatedly scans through a defined frequency range.

23. Apparatus as in claim 1 including a microscope having means for forming a magnified image of an object, wherein the means for forming said selected image comprises means for forming on the medium an image whose sharpness is functionally related to that of the magnified image, thereby deriving a signal which is functionally related to the degree of sharpness of the magnified image.

24. Apparatus as in claim 1 including an optical system providing an image modulated thereby, wherein the means for forming said selected image comprises means for forming on the medium an image whose sharpness is functionally related to that of the modulated image, thereby deriving a signal which is functionally related to the degree of sharpness of the modulated image.

25. Apparatus as in claim 1 including a range finder comprising a focussing lens system and a focussing ring with distance marking, wherein the means for forming said selected image comprises means for forming on the medium an image whose sharpness is functionally related to that of the image formed by said focussing lens system and to the position of the focussing ring, thereby deriving a signal which has an optimum value for a focussing ring setting corresponding to a distance marking for the distance between a selected scene and the lens system.

26. Apparatus as in claim 1 including an optical system having a first element and a second element, means for modulating an image with the combination of the two elements, means for changing the position of the two elements with respect to each other, wherein the means for forming said selected image comprises means for forming on the medium an image whose sharpness is functionally related to that of the modulated image, thereby deriving a signal functionally related to the degree of sharpness of the modulated image.

27. A method for detecting the sharpness of an image comprising:

providing a medium having a measurable property which varies as a function of the intensity pattern of an image formed thereon and as a function of strain disturbances in the medium;

forming a selected image on the medium;

causing a selected strain disturbance in the medium which propagates along the image formed thereon; and

measuring said property while the selected image is formed on the medium and while the selected strain disturbance is present therein to derive thereby a signal which is a Fourier transform representation of an aspect of the entire image and which represents the sharpness of the entire selected image formed on the medium and is substantially independent of the average intensity of the image formed on the medium and utilizing said signal for control purposes.

28. A method as in claim 27 wherein the selected strain disturbance is periodic in time and space.

29. A method as in claim 28 wherein said selected strain disturbance is a strain wave propagating through the portion of the medium on which the selected image is formed.

30. A method as in claim 29 wherein said strain wave is a surface wave propagating through the medium.

31. A method as in claim 27 wherein the property of the medium varies as a function of the variations in the intensity pattern of the image along a single selected dimension of the selected image.

32. A method as in claim 27 wherein the property of the medium varies as a function of the intensity pattern along at least two dimensions of the selected image.

33. A method as in claim 27 wherein the strain disturbance is a strain wave propagating through the medium, the signal derived is an electrical signal whose magnitude substantially corresponds to a Fourier transform representation of the intensity pattern along at least one dimension of the selected image for the spatial frequency of the strain wave.

34. A method as in claim 27 wherein the selected image is functionally related to at least a portion of a desired photograghic image formed by an objective lens and including the step of changing the focusing of said objective lens in accordance with the magnitude of the measured signal.

35. A method as in claim 27 wherein the selected image formed on said medium is functionally related to a photographic image projected by a projector lens on a screen plane, and including the step of focusing said projector lens in accordance with the magnitude of the derived signal.

39. A system as in claim 29 wherein said strain disturbance includes at least one strain wave whose spatial wavelength is substantially shorter than the size of the image formed on the medium and the signal comprises an indication of the term of the Fourier series representation of the image formed on the medium which corresponds to said wavelength.

40. A system as in claim 29 including means responsive to said signal for changing the focusing of said lens in accordance with the signal.

36. A method for detecting the sharpness of an image comprising:

obtaining selected high frequency components of the spatial Fourier transform of an image by modulating an electrical property of a body by the interaction of the image and strain waves in the body which have frequency characteristics corresponding to said components;

measuring the intensity of said high frequency components;

providing a signal which is indicative of the magnitude of said measured intensity and of the sharpness of the image; and

utilizing said signal for sharpness controlling purposes.

37. Apparatus for detecting the sharpness of an image comprising:

means for obtaining the spatial Fourier transform of an image including a body and means for modulating an electrical property of the body by causing the interaction therein of the image and strain waves having frequency characteristics corresponding to selected high spatial frequency components of said transform;

means for detecting the intensity of said selected high frequency components of the spatial Fourier transform of the image;

means for providing a signal indicative of said intensity and of the image sharpness; and

means for utilizing said signal for sharpness controlling purposes.

38. A system comprising:

a lens assembly for forming an image of a scene onto an image receiving surface and means for changing the focusing of said lens assembly to hereby change the sharpness of the image formed on said image receiving surface;

a medium and means for forming on said medium an image whose sharpness is functionally related to that of the image formed on said surface;

means for propagating a selected strain disturbance in the medium along the image formed thereon; and

means for measuring a selected property of the medium while said image is formed thereon and said disturbance is present therein and for deriving thereby a signal whose steady state represents the sharpness of the image formed on the medium.

42. A method as in claim 38 wherein the strain disturbance includes at least one spatial wavelength which is substantially shorter than the size of the image and the signal corresponds to the term of the Fourier series representation of the image formed on the medium which corresponds to said wavelength.

41. A method comprising the steps of:

forming the image of a scene onto a medium;

propagating a selected strain disturbance in the medium along the image formed thereon;

measuring a selected property of the medium while said image is formed thereon and said strain disturbance is present therein and deriving thereby a signal whose steady state level represents the sharpness of the image formed on the medium; and

utilizing the signal indicating the sharpness of the image for control purposes.

43. Apparatus for detecting the sharpness of an image represented by a beam at a selected plane transverse to the beam comprising:

a first device and a second device;

means for forming a first pattern on the first device and a second pattern on the second device, the sharpness of the first pattern coresponding to the image sharpness at a first plane on one side of said selected plane along the beam axis and the sharpness of the second pattern coresponding to the image sharpness at a second plane on the other side of said selected plane along the beam axis;

means for causing in said first and second devices interactions of said first and second pattern respectively and selected strain disturbances and for deriving therefrom respective first and second signals determined by selected high spatial frequency Fourier transform components of the first and second patterns respectively; and

means for combining said first and second signals to find a detection signal representing the degree of sharpenss of the image at said selected plane.

44. Apparatus as in claim 43 wherein said combining means includes means for deriving a direction signal representing the direction along the beam axis from the selected plane toward the plane of best sharpness.

45. Apparatus as in claim 44 wherein each of said devices comprises a medium having an electrical property varying with strain disturbances in the medium and with the intensity distribution of light on the medium, and the deriving means for each device include means for measuing said property of the medium while said strain disturbances are present and while the pattern is formed on the medium to thereby derive said signal representing the sharpness of the pattern.

46. Apparatus as in claim 43 including means for supporting the first and second devices at respective first and second positions which are spaced from each other along the beam axis and flank the selected plane.

47. Apparatus as in claim 43 including means for supporting said first and second devices at a common position with respect to the selected plane.

48. Apparatus as in claim 47 including optical means interposed between the beam and at least one of the devices to form on the two devices patterns correponding to two different image planes spaced from each other along the beam axis.

49. Apparatus as in claim 43 wherein the combining means comprises means for comparing said and first and second signals and for providing a detection signal corresponding to the degree of imbalance between the first and second signals.

50. Apparatus as in claim 43 wherein each of said devices comprises a medium capable of propagating strain disturbances at spatial frequencies extending through a defined range and having an electrical property varying with said spatial freqencies and with the intensity distribution of a pattern formed on the medium, and the means for causing said interaction and deriving said signals comprise, for each device, means for causing strain disturbances in the medium at a subset of spatial frequencies which is small as compared with said range, and means for measuring said electrical property on the medium while a pattern is formed on the medium and while said subset of strain disturbances is present to derive said signal representing transform components of the pattern.

51. Apparatus as in claim 50 including an optical system for viewing a scene and forming said image beam by modulating the scene in accordance with characteristics of the optical system, whereby the detection signal represents the degree of sharpness of the modulated image at a selected plane with respect to the optical system and therefore represents characteristics of the optical system.

52. Apparatus for detecting the quality of an image represented by a beam at a selected plane transverse to the beam comprising:

a first device and second device;

means for forming a first pattern on the first device and a second pattern on the second device, the quality of the first pattern corresponding to the image quality at a first plane on one side of the selected plane along the beam axis and the quality of the second pattern corresponding to the image quality at a second plane on the other side of said selected plane along the beam axis;

means for causing in said first and second device respective interactions between the first and second pattern and selected strain waves and for deriving therefrom respective first and second signals corresponding to selected high spatial frequency Fourier transform components of the first and second patterns respectively; and

means for combining the first and second signals to find a detection signal representing the quality of the image at the selected plane.

53. Apparatus as in claim 52 wherein said detection signal represents the degree of sharpness of the image at the selected plane and the direction along the beam axis from the selected plane towards the plane of best sharpness of the image.

54. Apparatus as in claim 52 wherein each device is capable of providing a range of Fourier transform components of the respective pattern and wherein the deriving means derives components corresponding to a subset of high spatial frequencies which is small as compared with said range.

55. A method of detecting the sharpness of an image represented by a beam at a selected plane transverse to the beam comprising the steps of:

providing a first device and a second device;

forming a first pattern on the first device and a second pattern on the second device, the sharpness of the first pattern corresponding to the image sharpness at a first plane on one side of said selected plane along the beam axis and the sharpness of the second pattern corresponding to the image sharpness at a second plane on the other side of said selected plane along the beam axis;

causing in each device an interaction of the respective pattern and selected strain waves in the device;

deriving from said first and second devices respective first and second signals determined by the respective interactions and corresponding to selected high spatial frequency Fourier transform components of the first and second patterns respectively; and

combining said first and second signals to find a detection signal representing the degree of sharpness of the image at said selected plane.

56. A method as in claim 55 wherein said combining step includes deriving a direction signal representing the direction along the beam axis from the selected plane toward the plane of best sharpness.

57. A method as in claim 55 wherein each device is capable of providing transform components of the respective pattern corresponding to a range of spatial frequencies and wherein the deriving step comprises deriving components corresponding to a subset of said spatial frequencies which is small as compared to said range.

58. A method of detecting the quality of an image formed by an optical system comprising the steps of:

providing a device and forming on the device a pattern whose quality is functionally related to the image quality at said selected plane;

causing in the device an interaction of the pattern and selected strain waves of arbitrarily selected frequency characteristics;

deriving from said device signals determined by said interaction and corresponding to selected high spatial frequency Fourier transform components of the pattern by the interaction of an image of the pattern and strain waves propagating in a medium of selected acousto-electrical properties; and

combining said signals to find a detection signal representing the quality of the image at said selected plane.

59. A method as in claim 58 including the step of modifying the optical system in accordance with the detection signal to thereby modify the image provided by the system.

60. A method as in claim 58 wherein the causing step comprises causing strain waves within a frequency range which is small as compared to the range of frequencies of the strain waves that the device is capable of propagating.