Three-dimensional calibration using orientation and position sensitive calibration pattern

• US 7,623,274 B1
• Filed: 12/22/2004
• Issued: 11/24/2009
• Est. Priority Date: 12/22/2004
• Status: Active Grant

• Current Assignee: Google LLC (Alphabet Inc.)
• Original Assignee: Google Inc. (Alphabet Inc.)
• Inventors: Lefevere, Francois-Marie
• Primary Examiner(s): Safaipour; Houshang
• Application Number:
  US11/020,388
• Time in Patent Office: 1,798 Days
• Field of Search: 358/474, 358/493, 358/497, 358/488, 358/461, 358/406
• US Class Current: 358/474
• CPC Class Codes: H04N 1/00002 Diagnosis, testing or measuring; Detecting, analysing or monitoring not otherwise provided for error detection, error correction or monitoring in digital computers or digital computer components G06F11/00
• CPC Class Codes: H04N 1/00013 Reading apparatus
• CPC Class Codes: H04N 1/00031 Testing, i.e. determining the result of a trial H04N1/00029 takes precedence; using test signals for transmission mode changing H04N2201/33371
• CPC Class Codes: H04N 1/00045 using a reference pattern designed for the purpose, e.g. a test chart
• CPC Class Codes: H04N 1/00053 out of service, i.e. outside of normal operation
• CPC Class Codes: H04N 1/00063 using at least a part of the apparatus itself, e.g. self-testing
• CPC Class Codes: H04N 1/00087 Setting or calibrating picture signal circuits H04N1/40
• CPC Class Codes: H04N 1/195 the array comprising a two-dimensional array or a combination of two-dimensional arrays
• CPC Class Codes: H04N 1/19594 using a television camera or a still video camera
• CPC Class Codes: H04N 2201/0434 specially adapted for scanning pages of a book
• CPC Class Codes: H04N 2201/0448 for positioning scanning elements not otherwise provided for; Aligning, e.g. using an alignment calibration pattern

Abstract

Systems and methods using an orientation/position-sensitive calibration pattern for three-dimensional calibration of an imaging system, such as one used in a process for scanning documents are disclosed. The method generally includes positioning the pattern on a support, capturing images using cameras to be calibrated, each image containing at least a unique orientation and position sensitive sub-area of the pattern, determining a set of coordinate pairs of corresponding points in the image and the pattern for each image utilizing image data and pattern information, and performing optimization utilizing the sets of coordinate pairs to calibrate relative position, orientation, zoom, and/or lens distortion, etc. of each camera so as to construct a three-dimensional camera calibration model. The pattern is generally comprised of overlapping sub-areas of a minimum portion of the pattern.

Claims

1. A method, comprising:

positioning an orientation and position sensitive calibration pattern on a support, the calibration pattern having a plurality of sub-areas unique within the calibration pattern, each unique sub-area being orientation sensitive and each unique sub-area being position sensitive within the calibration pattern;

capturing images using cameras to be calibrated, each image containing at least one of the unique sub-areas of the calibration pattern;

determining a set of coordinate pairs for each image utilizing image data and pattern information regarding the calibration pattern, each coordinate pair including coordinates of corresponding points in the image and in the calibration pattern; and

performing optimization utilizing the sets of coordinate pairs for each image to calibrate at least one of relative position, orientation, zoom, lens distortion of each camera so as to construct a three-dimensional calibration model of the camera.

2. The method of claim 1, further comprising:

repositioning the calibration pattern at a different position on the support; and

repeating said capturing and determining.

3. The method of claim 1, wherein said capturing, and determining are performed at least four times.

4. The method of claim 1, wherein the calibration pattern is generally composed of generally same sized, overlapping unique sub-areas and each sub-area is an area of a predetermined minimum portion of the calibration pattern, the sub-area being position sensitive within the calibration pattern by being patterned differently from other sub-areas in the calibration pattern.

5. The method of claim 1, wherein the support is configured to support a target object to be imaged, the target object being selected from the group consisting of a bound document and an unbound document.

6. The method of claim 1, wherein the calibration pattern comprises features at least some of which being marked with an orientation/position marker, the combination of the features and markers within each sub-area rendering the sub-area unique within the calibration pattern and orientation and position sensitive.

7. The method of claim 1, wherein the calibration pattern comprises a grid of features comprising alternating colored blocks, at least some of the features being marked with an orientation/position marker, the combination of the features and markers within each sub-area rendering the sub-area unique within the calibration pattern and orientation and position sensitive.

8. The method of claim 7, wherein the blocks are squares of approximately equal size and each marker is of a size smaller than each block.

9. The method of claim 7, wherein the alternating colored blocks are alternating dark and light blocks.

10. The method of claim 9, wherein a dark block is generally black and a light block is generally white and wherein a marker in a black block is generally white and a marker in a white block is generally black.

11. The method of claim 9, wherein the calibration pattern comprises alternating generally black and generally white square blocks forming the grid, the sub-area of the calibration pattern being an area of a predetermined minimum N blocks×

M blocks.

12. The method of claim 11, wherein the calibration pattern comprises 7 blocks×

9 blocks and the sub-area is an area of a minimum 4 blocks×

4 blocks.

13. A computer program product embodied on a computer readable medium, the computer program product including instructions that, when executed by a processor, cause the processor to perform actions comprising:

positioning an orientation and position sensitive calibration pattern on a support, the calibration pattern having a plurality of sub-areas unique within the calibration pattern, each unique sub-area being orientation sensitive and each unique sub-area being position sensitive within the calibration pattern;

capturing images using cameras to be calibrated, each image containing at least one of the unique sub-areas of the calibration pattern;

determining a set of coordinate pairs for each image utilizing image data and pattern information regarding the calibration pattern, each coordinate pair including coordinates of corresponding points in the image and in the calibration pattern; and

performing optimization utilizing the sets of coordinate pairs for each image pattern to calibrate at least one of relative position, orientation, zoom, lens distortion of each camera so as to construct a three-dimensional calibration model of the camera.

14. The computer program product of claim 13, further including instructions that, when executed by the processor, cause the processor to perform actions comprising:

repositioning the calibration pattern at a different position on the support; and

repeating said capturing and determining.

15. The computer program product of claim 13, wherein the capturing, and determining are performed at least four times.

16. The computer program product of claim 13, wherein the calibration pattern is generally composed of generally same sized, overlapping unique sub-areas and each sub-area is an area of a predetermined minimum portion of the calibration pattern, the sub-area being position sensitive within the calibration pattern by being patterned differently from other sub-areas in the calibration pattern.

17. The computer program product of claim 13, wherein the support is configured to support a target object to be imaged, the target object being selected from the group consisting of a bound document and an unbound document.

18. The computer program product of claim 13, wherein the calibration pattern comprises features at least some of which being marked with an orientation/position marker, the combination of the features and markers within each sub-area rendering the sub-area unique within the calibration pattern and orientation and position sensitive.

19. The computer program product of claim 13, wherein the calibration pattern comprises a grid of features comprising alternating colored blocks, at least some of the features being marked with an orientation/position marker, the combination of the features and markers within each sub-area rendering the sub-area unique within the calibration pattern and orientation and position sensitive.

20. The computer program product of claim 19, wherein the blocks are squares of approximately equal size and each marker being of a size smaller than each block.

21. The computer program product of claim 19, the alternating colored blocks are alternating dark and light blocks.

22. The computer program product of claim 21, wherein a dark block is generally black and a light block is generally white and wherein a marker in a black block is generally white and a marker in a white block is generally black.

23. The computer program product of claim 21, wherein the calibration pattern comprises alternating generally black and generally white square blocks forming the grid, the sub-area of the calibration pattern being an area of a predetermined minimum N blocks×

M blocks.

24. The computer program product of claim 23, wherein the calibration pattern comprises 7 blocks×

9 blocks and the sub-area is an area of a minimum 4 blocks×

4 blocks.

25. A system, comprising:

an orientation and position sensitive calibration pattern configured to be positioned on a support, the calibration pattern having a plurality of sub-areas unique within the calibration pattern, each unique sub-area being orientation sensitive and each unique sub-area being position sensitive within the calibration pattern;

at least one camera to be calibrated and configured to capture images containing at least one of the unique sub-areas of the calibration pattern positioned on the support; and

a signal processor configured to determine a set of coordinate pairs for each image utilizing image data and pattern information regarding the calibration pattern, each coordinate pair including coordinates of corresponding points in the image and in the calibration pattern, the signal processor is further configured to perform optimization utilizing the sets of coordinate pairs for each image to calibrate at least one of relative position, orientation, zoom, lens distortion of each camera so as to construct a three-dimensional calibration model of the camera.

26. The system of claim 25, wherein the signal processor is configured to perform the optimization by utilizing sets of coordinate pairs for at least 4 images captured by each camera.

27. The system of claim 25, further comprising the support configured to support a target object to be imaged, the target object being selected from the group consisting of a bound document and an unbound document.

28. The system of claim 25, wherein the calibration pattern is generally composed of generally same sized, overlapping unique sub-areas and each sub-area is an area of a predetermined minimum portion of the calibration pattern, the sub-area being position sensitive within the calibration pattern by being patterned differently from other sub-areas in the calibration pattern.

29. The system of claim 25, wherein the calibration pattern comprises features at least some of which being marked with an orientation/position marker, the combination of the features and markers within each sub-area rendering the sub-area unique within the calibration pattern and orientation and position sensitive.

30. The system of claim 25, wherein the calibration pattern comprises a grid of features comprising alternating colored blocks, at least some of the features being marked with an orientation/position marker, the combination of the features and markers within each sub-area rendering the sub-area unique within the calibration pattern and orientation and position sensitive.

31. The system of claim 30, wherein the blocks are squares of approximately equal size and each marker is of a size smaller than each block.

32. The system of claim 30, wherein the alternating colored blocks are alternating dark and light blocks.

33. The system of claim 32, wherein a dark block is generally black and a light block is generally white and wherein a marker in a black block is generally white and a marker in a white block is generally black.

34. The system of claim 32, wherein the calibration pattern comprises alternating generally black and generally white square blocks forming the grid, the sub-area of the calibration pattern being an area of a predetermined minimum N blocks×

M blocks.

35. The system of claim 34, wherein the calibration pattern comprises 7 blocks×

9 blocks and the sub-area is an area of a minimum 4 blocks×

4 blocks.