Global localization by fast image matching

• US 20050147299A1
• Filed: 01/07/2004
• Published: 07/07/2005
• Est. Priority Date: 01/07/2004
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Wang, Qiang, Dang, Yingnong, Wang, Jian, Chen, Liyong, Ma, Xiaoxu
• Granted Patent: US 7,463,774 B2
• Time in Patent Office: Days
• US Class Current: 382/181
• CPC Class Codes: G06F 3/0321 by optically sensing the absolute position with respect to a regularly patterned surface forming a passive digitiser, e.g. pen optically detecting position indicative tags printed on a paper sheet constructional details of pen-shaped pointing devices G06F3/03545, G06F3/03542, G06F3/037
• CPC Class Codes: G06F 3/03545 Pens or stylus

Abstract

An efficient technique is provided for determining a portion of a document corresponding to a captured image. Areas of a document in which the pattern is at least partially obscured are identified. A reference pixel in the image is selected, and an offset between the pixel and the pattern is determined. A pixel-by-pixel comparison is then made of the image with the document such that the reference pixel is only compared with locations in the document that are both within the identified areas and have the determined offset from the pattern. The comparison with the highest correspondence between the image pixels and the electronic document then identifies the position of the reference pixel relative to the electronic document.

Claims

1. A method of determining a portion of a document corresponding to a captured image, comprising:

obtaining a captured image of a portion of a document, the document having a pattern that uniquely identifies different positions in the document;

determining obscured areas of the document in which the pattern is at least partially obscured;

designating a reference pixel in the captured image;

identifying locations in the obscured areas of the document that may correspond with the reference pixel;

comparing the captured image with different portions of the document, such that the reference pixel is compared with one or more of the identified locations; and

based upon the comparison, determining an identified location in the document that corresponds with the reference pixel.

2. The method recited in claim 1, wherein identifying locations in the obscured areas of the document that may correspond with the reference pixel includes:

determining an offset distance between the reference pixel and the representation of the pattern in the captured image; and

identifying locations in the obscured areas of the document that are offset from the pattern by the offset distance.

3. The method recited in claim 1, further comprising warping the captured image so that the scale and rotation of the captured image match the scale and rotation of the document.

4. The method recited in claim 3, further comprising:

warping the captured image, and rotating the warped captured image at multiples of 90°

.

5. The method recited in claim 4, wherein comparing the captured image with different portions of the document includes comparing each rotated warped captured image with the different portions of the document.

6. The method recited in claim 1, wherein the document is an electronic document.

7. The method recited in claim 1, wherein determining an identified location in the document that corresponds with the reference pixel includes determining a correlation value for each comparison of the image with a portion of a document.

8. The method recited in claim 7, wherein determining an identified location in the document that corresponds with the reference pixel further includes identifying comparison values that have a correlation value of 0.5 or greater.

9. The method recited in claim 8, wherein determining an identified location in the document that corresponds with the reference pixel further includes

identifying a highest comparison correlation value that is higher than all other comparison correlation values by a threshold amount;

and

determining that the reference pixel corresponds to the document location employed in the comparison with the highest comparison correlation value.

10. The method recited in claim 9, wherein the threshold amount is 0.1.