Method for modifying the perspective of a digital image

• US 6,400,848 B1
• Filed: 03/30/1999
• Issued: 06/04/2002
• Est. Priority Date: 03/30/1999
• Status: Expired due to Term

• Current Assignee: Apple Inc.
• Original Assignee: Eastman Kodak Company
• Inventors: Gallagher, Andrew C.
• Primary Examiner(s): ROGERS, SCOTT A
• Application Number:
  US09/281,574
• Time in Patent Office: 1,162 Days
• Field of Search: 382/275, 382/254, 382/276, 382/286, 382/287, 382/293, 382/294, 382/154, 382/106, 382/104, 382/105, 382/199, 345/647
• US Class Current: 382/254
• CPC Class Codes: G06T 5/80 Geometric correction

Abstract

A method for modifying an apparent perspective of a digital image representing a perspective projection of a scene, the method comprises the steps of locating a line in the digital image; computing a correction term based on parameters of the located line which said correction term is related to the perspective of the digital image relative to the scene; and resampling the digital image based on the correction term for creating a processed image.

Claims

1. A method for modifying an apparent perspective of a digital image representing a perspective projection of a scene, the method comprising the steps of:

(a) locating a line in the digital image;

(b) computing a correction term based on parameters of the located line which said correction term is related to the perspective of the digital image relative to the scene; and

(c) resampling the digital image based on the correction term for creating a processed image.

2. The method of claim 1, wherein step (b) further comprises:

(b1) calculating the correction term such that when the digital image is resampled in step (c) the located line is substantially vertical in the processed image.

3. The method of claim 2, wherein step (b) further comprises computing a vanishing point for the located line.

4. The method as in claim 3, wherein step (b) further comprises computing the correction term based on the following formula:

5. The method as in claim 3, wherein step (b) further comprises computing the correction term based on the following formula:

6. The method as in claim 1, wherein step (a) further comprises the steps of:

(a1) generating an edge image from the digital image

(a2) computing a Hough transform of the edge image; and

(a3) detecting peaks of a Hough accumulator; and

(a4) identifying the peaks of the Hough accumulator which correspond to a located line in the digital image.

7. The method as in claim 6, wherein step (a1) further comprises the steps of:

(a11) blurring the digital image with a digital filter;

(a12) calculating a gradient of the blurred digital image; and

(a13) applying a threshold to the gradient of the blurred digital image for producing the edge image.

8. The method as in claim 6, wherein step (a3) further comprises the steps:

(a31) filtering the Hough accumulator with a matched filter;

(a32) generating a difference accumulator with the filtered Hough accumulator and the Hough accumulator;

(a32) applying a threshold to the difference accumulator creating a peak image;

(a33) identifying local maximum values of the peak image; and

(a34) if the local maximum is nonzero and equal to the value of the peak image at any particular location, identifying that location as a peak value.

9. The method as in claim 6, wherein step (a4) further comprises the steps of:

(a41) identifying those peak values of step (a3) that correspond to located lines.

10. The method as in claim 1, wherein step (c) further comprises the steps of:

(c1) re-sampling a row of pixels of the digital image such that the rate of interpolation is dependent on the correction term, and a position of the row of pixels with respect to the central row of pixels; and

(c2) repeating step (c1) for all the other rows of pixels.

11. A method for modifying a perspective of a digital image, the method comprising the steps of.

(a) subsampling the digital image;

(b) locating a line in the sub-sampled digital image;

(c) computing a correction term based on parameters of the located line which said correction term is related to the perspective of the digital image relative to the scene; and

(d) resampling the digital image based on the correction term for creating a processed image.

12. A computer program product for modifying an apparent perspective of a digital image representing a perspective projection of a scene, comprising:

a computer readable storage medium having a computer program stored thereon for performing the steps of;

(a) locating a line in the digital image;

(b) computing a correction term based on parameters of the located line which said correction term is related to the perspective of the digital image relative to the scene; and

(c) resampling the digital image based on the correction term for creating a processed image.

13. The computer program product of claim 12, wherein step (b) further comprises:

(b1) calculating the correction term such that when the digital image is resampled in step (c) the located line is substantially vertical in the processed image.

14. The computer program product of claim 13, wherein step (b) further comprises computing a vanishing point for the located line.

15. The computer program product as in claim 14, wherein step (b) further comprises computing the correction term based on the following formula:

16. The computer program product as in claim 14, wherein step (b) further comprises computing the correction term based on the following formula:

17. The computer program product as in claim 12, wherein step (a) further comprises:

(a1) generating an edge image from the digital image

(a2) computing a Hough transform of the edge image; and

(a3) detecting peaks of a Hough accumulator; and

(a4) identifying the peaks of the Hough accumulator which correspond to a located line in the digital image.

18. The computer program product as in claim 17, wherein step (a1) further comprises the steps of:

(a11) blurring the digital image with a digital filter;

(a12) calculating a gradient of the blurred digital image; and

(a13) applying a threshold to the gradient of the blurred digital image for producing the edge image.

19. The computer program product as in claim 17, wherein step (a3) further comprises the steps:

(a31) filtering the Hough accumulator with a matched filter;

(a32) generating a difference accumulator with the filtered Hough accumulator and the Hough accumulator;

(a32) applying a threshold to the difference accumulator creating a peak image;

(a33) identifying local maximum values of the peak image; and

(a34) if the local maximum is nonzero and equal to the value of the peak image at any particular location, identifying that location as a peak value.

20. The computer program product as in claim 17, wherein step (a4) further comprises the steps of:

(a41) identifying those peak values of step (a3) that correspond to located lines.

21. The computer program product as in claim 13, wherein the re-sampling means further comprises:

(c1) means for re-sampling a row of pixels of the digital image such that the rate of interpolation is dependent on the correction term, and a position of the row of pixels with respect to the central row of pixels; and

(c2) means for repeating the means (c1) for all the other rows of pixels.

22. A system for modifying an apparent perspective of a digital image representing a perspective projection of a scene, the system comprising:

(a) means for locating a line in the digital image;

(b) means for computing a correction term based on parameters of the located line which said correction term is related to the perspective of the digital image relative to the scene; and

(c) means for resampling the digital image based on the correction term for creating a processed image.

23. The system of claim 22, wherein the computing means further comprises:

(b1) the calculating means includes the correction term such that when the digital image is resampled in step (c) the located line is substantially vertical in the processed image.

24. The system of claim 23, wherein the calculating means further comprises means for computing a vanishing point for the located line.

25. The system as in claim 24, wherein the calculating means further comprises means for computing the correction term based on the following formula:

26. The system as in claim 24, wherein the calculating means further comprises computing the correction term based on the following formula:

27. The system as in claim 22, wherein step (a) further comprises:

(a1) means for generating an edge image from the digital image

(a2) means for computing a Hough transform of the edge image; and

(a3) means for detecting peaks of a Hough accumulator; and

(a4) means for identifying the peaks of the Hough accumulator which correspond to a located line in the digital image.

28. The system as in claim 27, wherein the generating means further comprises the steps of:

(a11) blurring the digital image with a digital filter;

(a12) calculating a gradient of the blurred digital image; and

(a13) applying a threshold to the gradient of the blurred digital image for producing the edge image.

29. The system as in claim 27, wherein the detecting means further comprises:

(a31) means for filtering the Hough accumulator with a matched filter;

(a32) means for generating a difference accumulator with the filtered Hough accumulator and the Hough accumulator;

(a32) means for applying a threshold to the difference accumulator creating a peak image;

(a33) means for identifying local maximum values of the peak image; and

(a34) if the local maximum is nonzero and equal to the value of the peak image at any particular location, means for identifying that location as a peak value.

30. The system as in claim 27, wherein the identifying means further comprises:

(a41) means for identifying those peak values of step (a3) that correspond to located lines.

31. The system as in claim 22, wherein step (c) further comprises:

(c1) means for re-sampling a row of pixels of the digital image such that the rate of interpolation is dependent on the correction term, and a position of the row of pixels with respect to the central row of pixels; and

(c2) repeating the means (c1) for all the other rows of pixels.