Method for simultaneously compositing a panoramic image and determining camera focal length

• US 6,256,058 B1
• Filed: 06/06/1996
• Issued: 07/03/2001
• Est. Priority Date: 06/06/1996
• Status: Expired due to Term

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Compaq Computer Corporation (HP Inc.)
• Inventors: Weiss, Richard S., Kang, Sing Bing
• Primary Examiner(s): Faile, Andrew I.
• Assistant Examiner(s): Ho, Tuan V.
• Application Number:
  US08/660,704
• Time in Patent Office: 1,853 Days
• Field of Search: H04/N.5225, 348/207, 348/177, 348/178, 348/180, 348/181, 348/187, 348/188, 348/36, 348/37, 348/38, 348/39, 348/345, 348/357, 348/335, 356/243, 250/201.2, 382/106, 382/284
• US Class Current: 348/207.99
• CPC Class Codes: H04N 23/698 for achieving an enlarged field of view, e.g. panoramic image capture
• CPC Class Codes: H04N 5/2624 for obtaining an image which is composed of whole input images, e.g. splitscreen

Abstract

In a computerized image processing system, a camera acquires a set of images of a scene while rotating the camera about an axis passing through an optical center of the camera. The images of the set overlap each other. An initial estimate of the focal length of the camera is made. The initial focal length can be any reasonable focal length. Using the initial estimate of the focal length, the set of images are composited in a memory to determine an estimated initial composited length. A next best estimate of the focal length is derived from the initial estimated composited length. The set of images are recomposed using the next best focal length estimate. This process is iterated until the absolute difference between the successive estimates of the focal length is less than a predetermined threshold to calibrate the camera. In addition, the process of compositing the set of images can use a weighted interpolation scheme to reduce the blurring effects caused by noise and digitization effects and incorrect focal length.

Claims

1. A computer implemented method for calibrating a camera comprising:

acquiring a set of planar images of a scene while rotating the camera such that the planar images of the set overlap each other;

estimating a current focal length of the camera;

compositing the set of planar images in a memory of a computer to determine a current composited length of a set of cylindrical images using the current focal length;

deriving a next focal length from the current composited length;

recompositing the set of images in the memory to determine a next composited length using the next focal length;

selecting the next focal length as the focal length of the camera if the absolute difference between the next focal length and the current focal length is less than a predetermined threshold.

2. The method of claim 1 further comprising:

iterating the deriving and recompositing steps by assigning the next focal length as the current focal length until the absolute difference between the next focal length and the current focal length is less than the predetermined threshold.

3. The method of claim 1 further comprising:

arranging pixels for acquiring the set of images at the focal plane of the camera in regularly spaced rows and columns having a unit distance.

4. The method of claim 1 further comprising:

rotating the camera about an axis passing through the optical center of the camera.

5. The method of claim 4 further wherein the axis of rotation is substantially perpendicular to the optical axis of the camera.

6. The method of claim 5 further comprising:

rotating the camera to acquire a full 360 degree panoramic view of the scene.

7. The method of claim 1 further comprising:

estimating the current focal length of the camera to be a value larger or smaller than a correct focal length of the camera.

8. The method of claim 1 further comprising:

rotating the camera through an arbitrary angle which if offset for each image of the set to enable overlap between successively taken images.

9. The method of claim 1 further comprising:

using a weighted interpolation scheme in compositing the cylindrical images to reduce the blurring effects of camera noise, digitization, image interpolation, and the estimated current focal length.

10. The method of claim 9 wherein a particular pixel is weighted inversely proportional to a distance of the particular pixel from a central column of pixels of a particular image of the set.