System for registering component image tiles in a camera-based scanner device transcribing scene images

• US 5,581,637 A
• Filed: 04/16/1996
• Issued: 12/03/1996
• Est. Priority Date: 12/09/1994
• Status: Expired due to Fees

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Saund, Eric, Cass, Todd A.
• Primary Examiner(s): Mancuso, Joseph
• Application Number:
  US08/632,921
• Time in Patent Office: 231 Days
• Field of Search: 282/284, 282/287, 282/291, 282/294, 282/309, 282/130, 282/173, 282/174, 282/180, 348/262, 348/264
• US Class Current: 382/284
• CPC Class Codes: G06T 3/14 Transformations for image registration, e.g. adjusting or mapping for alignment of images
• CPC Class Codes: G06V 10/10 Image acquisition document image scanning and transmission H04N1/00; control of digital cameras H04N23/60
• CPC Class Codes: G06V 10/147 Details of sensors, e.g. sensor lenses fingerprint or palmprint sensors G06V40/13; vascular sensors G06V40/145; eye sensors G06V40/19
• CPC Class Codes: G06V 10/245 by locating a pattern; Special marks for positioning

Abstract

A device for registering component image tiles in a scanning system for transcribing, into electronic form, markings on a two-dimensional surface such as a whiteboard. A registration light pattern is projected onto the surface to be imaged. The pattern projected can be chosen to best suite the specific properties of the camera and imaging environment. The pattern markings are processed using perspective transformations to determine the overlap properties of the image tiles and distortion of each tile image, and the resulting data is used to combine the tiles to produce an undistorted composite image of the whiteboard.

Claims

1. A method for providing a complete undistorted computational representation of an image on a surface, the method comprising the steps of:

a) projecting a light pattern upon the image, the light pattern including a multiplicity of lightmarks, each lightmark having a neighborhood;

b) capturing a multiplicity of image tiles using at least one camera subsystem, each of the image tiles including a portion of the image and at least a one of the lightmarks, each image tile having an overlapping area for each adjacent image tile overlapped by the image tile;

c) converting the image tiles into a computational format;

d) for each image tile, identifying the overlapping areas;

e) correcting distortions of the image tiles, including perspective distortion, to produce a single undisturbed, computational representation of the image by the substeps of;

1) identifying the lightmarks within the overlapping areas;

2) performing local correlations of image patches in the neighborhoods of the lightmarks within the overlapping areas to identify locations in each image tile of the lightmarks within the overlapping areas;

3) projecting the lightmark locations into surface coordinates;

4) for each pair of overlapping, adjacent image tiles, comparing corresponding pairs of lightmarks within the overlapping area common to the pair of overlapping, adjacent image tiles;

5) for each pair of lightmarks within the overlapping area common to a pair of overlapping, adjacent image tiles, choosing target coordinates at a location intermediate to the surface coordinates of each of the pair of lightmarks within the overlapping area common to the pair of overlapping, adjacent image tiles;

6) computing perspective transforms for each image tile using the target coordinates for the lightmarks within the overlapping areas;

7) repeating substeps

     1)-6) until convergence upon locations of lightmarks within the overlapping area of each image tile that represent a cumulative error in surface coordinates of the lightmarks within the overlapping areas of each image tile that is less than a threshold amount.

2. The method of claim 1 wherein step e3) comprises the steps of:

for each pair of overlapping, adjacent image tiles;

A) finding a first location of a first liqhtmark of the lightmarks within the overlapping area common to the pair of overlapping, adjacent image tiles, the first location being within a surface co-ordinate system and being found given a location of the first lightmark within a first co-ordinate system associated with a first tile of the pair of overlapping, adjacent image tiles;

B) finding a second location of the first lightmark within the surface co-ordinate system given a location of the first lightmark within a second co-ordinate system associated with a second tile of the pair of overlapping adjacent, image tiles; and

wherein step e6) comprises the step of;

for each pair of overlapping adjacent image tile;

using the first location and the second location of the first lightmark to compute the perspective transform.

3. The method of claim 2, wherein step e6) includes the steps of:

computing a perspective transform of said first tile to obtain the first location of the first lightmark;

computing a perspective transform of said second tile to obtain the second location of the first lightmark; and

determining a difference between the first location and second location of said first lightmark.

4. The method of claim 2, wherein step e2) includes the steps of:

for each pair of overlapping, adjacent image tiles;

performing center-surround processing on said first tile to identify lightmarks; and

performing center-surround processing on said second tile to identify lightmarks.

5. An automatic system for capturing in computational form an undisturbed image content of an image comprising:

a) a surface upon which the image is provided;

b) at least one camera subsystem for capturing the image in a matrix of image tiles, each of the image tiles including at least a portion of the image, each of the image tiles having an overlapping area that overlaps an adjacent image tile;

c) a projection subsystem for projecting a registration pattern upon the image, the registration pattern including a multiplicity of lightmarks, each of the overlapping areas including at least one of the lightmarks;

d) a processor combining the image tiles to create in computational form the undisturbed image content of the image corrected for perspective distortion by the step of;

1) for each pair of adjacent image tiles, identifying a first overlapping area of a first image tile of the pair of adjacent image tiles corresponding to a second overlapping area of a second image tile of the pair of adjacent image tiles;

2) identifying a first lightmark in the first overlapping area corresponding to a second lightmark in the second overlapping area;

3) finding a projection of the first liqhtmark at a first surface coordinate location in the first image tile;

4) finding a projection of the second liqhtmark at a second surface coordinate location in the second image tile;

5) correcting perspective distortion between the first surface coordinate location and the second surface coordinate location; and

generating corrected surface coordinates for the first lightmark and the second lightmark;

e) memory coupled to the processor, the memory storing instructions for the processor and storing in computation form the undisturbed image content of the image.