Measuring distance using perspective

• US 20070076187A1
• Filed: 10/05/2005
• Published: 04/05/2007
• Est. Priority Date: 10/05/2005
• Status: Active Grant

• Current Assignee: Libre Holdings Incorporated
• Original Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Inventors: Boyd, David, Goris, Andrew
• Granted Patent: US 7,372,550 B2
• Time in Patent Office: Days
• US Class Current: 356/4.30
• CPC Class Codes: G01C 3/08 Use of electric radiation detectors
• CPC Class Codes: G06T 7/536 from perspective effects, e.g. by using vanishing points

Abstract

A method is disclosed for measuring distance from a camera to parts of a scene using a characterization of perspective distortion in a photograph of the scene. In one example embodiment, a first distance measurement is obtained from the camera to a first point in the scene, the perspective distortion is characterized, and the distance to at least one other point on a plane in the scene is computed based on the first distance measurement and the perspective characterization.

Claims

1. A method, comprising:

obtaining a measurement of a first distance from a camera to a first point in a scene;

characterizing perspective distortion in a photograph of the scene; and

computing at least one other axial distance from the camera to at least one other point on a plane in the scene, based on the first distance measurement and the perspective characterization.

2. The method of claim 1, wherein the first distance is the distance from the camera to a point in the scene on which the camera is focused.

3. The method of claim 2, wherein the first distance is derived from at least one position of one or more elements of a lens of the camera.

4. The method of claim 1, wherein characterizing perspective distortion further comprises identifying a dominant set of converging lines in the photograph.

5. The method of claim 4, wherein identifying a dominant set of converging lines further comprises repeated application of a Hough transform.

6. The method of claim 5, further comprising restricting the search range of at least the first of the Hough transforms.

7. The method of claim 5, further comprising identifying a vanishing point of the converging lines.

8. The method of claim 1, wherein computing at least one other axial distance further comprises:

locating a horizon for the photograph; and

computing the other axial distance in inverse proportion to the distance from the at least one other point in the photograph to the horizon.

9. The method of claim 8, wherein the horizon is horizontal.

10. The method of claim 8, wherein the horizon is vertical.

11. The method of claim 1, further comprising:

selecting a mode; and

choosing which of a horizontal horizon and a vertical horizon to use in computing distances, the choice based on the mode selection.

12. The method of claim 11, wherein the mode is designed for photographing documents, and wherein the horizontal horizon is used.

13. The method of claim 1, further comprising computing axial distances from the camera to the plane in at least two scene locations corresponding to corners of the photograph.

14. The method of claim 1, wherein the photograph is a preliminary photograph, and further comprising selecting a combination of a lens aperture and a focus distance such that all points on the plane are in acceptable focus in a final photograph of the scene.

15. The method of claim 14, wherein the focus distance is an axial distance to a scene location upon which the camera focused in obtaining the photograph used to characterize perspective.

16. The method of claim 1, further comprising:

locating a horizontal horizon for the photograph;

locating a vertical horizon for the photograph;

computing a range of axial distances from the camera to a first plane in the scene based on the horizontal horizon; and

computing a range of axial distances from the camera to a second plane in the scene based on the vertical horizon.

17. The method of claim 16, further comprising selecting a combination of a focus distance and a lens aperture such that scene features within all of both ranges are in acceptable focus in a subsequent photograph taken using the combination.

18. The method of claim 17, wherein the focus distance is an axial distance to a scene location upon which the camera focused in obtaining the photograph used to characterize perspective.

19. The method of claim 1, further comprising:

locating a horizontal horizon for the photograph;

locating a vertical horizon for the photograph;

performing the steps of characterizing perspective distortion and computing at least one other axial distance based on both horizons;

presenting both results to a user; and

enabling a user to select one of the results.

20. The method of claim 1, further comprising compensating for distance-related effects of on-camera flash illumination by post-processing a photograph based on the distance measurements.

21. The method of claim 1, performed in a camera.

22. The method of claim 1, wherein the plane is a plane that includes the first point in the scene, and on which parallel lines exhibit the same perspective distortion as is dominant in the photograph.

23. The method of claim 1, wherein characterizing perspective distortion in the photograph further comprises:

detecting edges in the photograph, producing a first edge-detected image;

performing a first Hough transform on the first edge-detected image, producing a first Hough accumulator;

detecting edges in the first Hough accumulator, producing a second edge-detected image;

performing a second Hough transform on the second edge-detected image, producing a second Hough accumulator;

finding a brightness peak in the second Hough accumulator;

performing an inverse Hough transform on the peak, producing a first line in the first Hough accumulator, the first line representing a set of dominant lines in the photograph;

performing an inverse Hough transform on at least two points on the first line, producing at least two corresponding lines similar to the set of dominant lines in the photograph; and

finding an intersection of the corresponding lines.

24. The method of claim 1, further comprising:

recording the first distance measurement with the photograph; and

subsequently performing the steps of characterizing perspective distortion and computing at least one other axial distance.

25. The method of claim 1, further comprising:

correcting at least one form of distortion in the photograph other than perspective distortion; and

subsequently performing the steps of characterizing perspective distortion and computing at least one other axial distance.

26. The method of claim 25, wherein the form of distortion other than perspective distortion is either lens barrel distortion or lens pincushion distortion.

27. A camera, comprising logic, the logic configured to perform the following method:

obtaining a measurement of a first distance from a camera to a first point in a scene;

characterizing perspective distortion in a photograph of the scene; and

computing at least one other axial distance from the camera to at least one other point on a plane in the scene, based on the first distance measurement and the perspective characterization

28. The camera of claim 27, further comprising a lens, and wherein the first distance is the distance from the camera to the point in the scene on which the lens is focused.

29. The camera of claim 28, wherein the first distance is derived from at least one position of at least one lens element.

30. The camera of claim 27, wherein characterizing perspective distortion further comprises identifying a dominant set of converging lines in the photograph.

31. The camera of claim 30, wherein identifying the dominant set of converging lines further comprises repeated application of a Hough transform.

32. The camera of claim 27, wherein computing at least one other axial distance further comprises:

locating a horizon for the photograph; and

computing the axial distance as in inverse proportion to the distance from the location of the point in the photograph to the horizon.

33. A system, comprising:

a camera; and

acomputer; and

wherein;

the camera takes a photograph of a scene;

the camera measures a first distance from the camera to a first point in the scene;

the photograph and the first distance measurement are transferred to the computer;

the computer characterizes perspective distortion in the photograph; and

the computer computes at least one other axial distance to at least one other point on a plane in the scene using the first distance measurement and the perspective characterization.

34. A camera, comprising:

means for obtaining a first measurement of a first distance from the camera to a first point in a scene;

means for characterizing perspective distortion in a photograph of the scene; and

means for computing at least one other axial distance to at least one other point on a plane in the scene using the first distance measurement and the characterization of perspective distortion.

35. The camera of claim 34, further comprising means for performing a repeated Hough transform on the photograph.

36. A method, comprising:

characterizing perspective distortion in a photograph of a scene; and

computing, based on the perspective characterization, relative distances from a camera used to take the photograph to points on a plane in the scene.

37. The method of claim 36, wherein characterizing perspective distortion further comprises identifying a dominant set of converging lines in the photograph.

38. The method of claim 37, wherein identifying a dominant set of converging lines further comprises repeated application of a Hough transform.

39. The method of claim 36, wherein computing relative distances from the camera to points on the plane in the scene further comprises:

locating a horizon for the photograph; and

computing the distances from the camera to points on the plane in inverse proportion to distances from points in the photograph to the horizon.

40. The method of claim 36, wherein characterizing perspective distortion in the photograph further comprises:

detecting edges in the photograph, producing a first edge-detected image;

performing a first Hough transform on the first edge-detected image, producing a first Hough accumulator;

detecting edges in the first Hough accumulator, producing a second edge-detected image;

performing a second Hough transform on the second edge-detected image, producing a second Hough accumulator;

finding a brightness peak in the second Hough accumulator;

performing an inverse Hough transform on the peak, producing a first line in the first Hough accumulator, the first line representing a set of dominant lines in the photograph;

performing an inverse Hough transform on at least two points on the first line, producing at least two corresponding lines similar to the set of dominant lines in the photograph; and

finding an intersection of the corresponding lines.

41. The method of claim 36, further comprising using the distance information in post-processing the photograph.

42. The method of claim 41, wherein post-processing the photograph further comprises compensating for distance-related unevenness of flash illumination.

43. A camera, comprising logic, the logic configured to perform the following method:

characterizing perspective distortion in a photograph of a scene; and

computing, based on the perspective characterization, relative distances from the camera to points on a plane in the scene.