Curled surface imaging system

• US 6,885,479 B1
• Filed: 07/07/2000
• Issued: 04/26/2005
• Est. Priority Date: 07/09/1999
• Status: Expired due to Term

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Inventors: Pilu, Maurizio
• Primary Examiner(s): Lee, Cheukfan
• Application Number:
  US09/786,768
• Time in Patent Office: 1,754 Days
• Field of Search: 358/488, 358/474, 358/909.1, 358/448, 358/475, 358/463, 358/525, 358/497, 358/494, 358/471, 358/486, 358/464, 358/465, 358/466, 358/493, 382/291, 382/293, 382/285, 382/300, 382/318, 382/319, 382/312, 382/286, 348/96, 399/362, 355/25, 250/234, 250/235, 250/236, 356/602, 356/603, 356/604
• US Class Current: 358/474
• CPC Class Codes: H04N 1/195 the array comprising a two-dimensional array or a combination of two-dimensional arrays
• CPC Class Codes: H04N 1/387 Composing, repositioning or otherwise geometrically modifying originals
• CPC Class Codes: H04N 2201/0434 specially adapted for scanning pages of a book
• CPC Class Codes: H04N 2201/0452 Indicating the scanned area, e.g. by projecting light marks onto the medium

Abstract

The present invention relates to a system for de-warping images of a developable surface, including developable curled surfaces, and in particular of images of curled documents (30). The system (1) includes a processor (25) linked to an image capture means (2) which: captures an image of the surface (30), said image having a warp corresponding to the non-planar surface; generates from the image a first set of points representing the three-dimensional profile of the non-planar surface relative (30) to a planar reference surface (12); fits to the first set of points a second set of points representative of a developable mesh; and uses the second set of points to texture-map the image (12) in order to de-warp the image.

Claims

1. An imaging system for imaging a non-planar developable surface, the system comprising:

a processor linked to an imaging detector and being capable of;

capturing at least one image of the surface, said image having a warp corresponding to the non-planar surface; and

of

generating therefrom a first set of points representing the three-dimensional profile of the non-planar surface relative to a planar reference surface,

wherein the processor is arranged to fit to the first set of points, a second set of points representative of a developable mesh and to use the second set of points to texture-map the image in order to de-warp the image.

2. An imaging system as claimed in claim 1, further comprising a projector which is arranged in an assigned fixed position with respect to the imaging detector for projecting a structured light pattern that forms separate light stripes across the non-planar surface.

3. An imaging system as claimed in claim 2, wherein the processor is configured to develop the first set of points from the light stripes.

4. A method of imaging a non-planar developable surface using an imaging system comprising a processor linked to an imaging detector, comprising the steps of:

i) capturing at least one image of the surface, said image having a warp corresponding to the non-planar surface;

ii) generating from the image a first set of points representing the three-dimensional profile of the non-planar surface relative to a planar reference surface;

iii) fitting to the first set of points, a second set of points representative of a developable mesh; and

iv) using the second set of points to texture-map the image in order to de-warp the image.

5. A method as claimed in claim 4, in which in step iii) the mesh is distorted as the second set of points is fit to the first set of points to the extent that the mesh is no longer developable, following which the distorted mesh is relaxed to a developable state.

6. A method as claimed in claim 5, in which prior to step iii) an initial surface is fit to the first set of points, and in step iii) the mesh is fit to the initial surface.

7. A method as claimed in claim 6, in which the initial surface is a developable surface, and in which, after fitting of the mesh to the initial surface, at least some of the second set of points are moved closer to corresponding ones of the first set of data points during which the mesh is distorted.

8. A method as claimed in claim 5, in which the relaxation of the mesh takes place in an iterative process in which the second set of points is adjusted incrementally until distances between points in the second set of points are equalized.

9. A method as claimed in claim 4, in which points in the second set of points are not fit to the first set of points if said points in the second set of points do not correspond closely enough to any of the points in the first set of points.

10. A method as claimed in claim 4, in which the non-planar developable surface is a curled document.

11. A method as claimed in claim 10, in which the extent of the document is estimated by fitting a rectangle around extreme points of the first set of points.

12. A method as claimed in claim 10, in which the imaging detector projects a structured light pattern that forms separated light stripes across the non-planar developable surface, the first set of points being generated from the light stripes.

13. A method as claimed in claim 12, in which step ii) includes the steps of:

a) creating a difference image by taking a difference between an image captured with the stripes and an image captured without the stripes;

b) thresholding the difference image to discard portions below a threshold;

c) counting detected stripes across the difference image in order to identify individual stripes; and

d) triangulating the image of the non-planar surface at points corresponding with identified stripes to generate the first set of points.