US 5,901,253 A · Image processing system with image cropping and skew correction

Abstract

An arrangement is described for determining the skew angle of a document image without requiring text or other skew detection information in the document or without human intervention. The arrangement accomplishes this by determining an edge of the document image within a scan image and uses that edge to determine the skew angle of the document image. The edge can be determined by locating the first or last document image pixel of each scan line of pixels in the scan image that belongs to the document image. This is accomplished by comparing each pixel of each scan line of pixels with a predetermined scan line of background pixels. The skew angle of the document image is then determined by computing the slope of the detected edge in the scan image. An arrangement of determining the boundary of the document image is also described. The arrangement does this by locating (1) a first document image pixel and a last document image pixel for the first scan line of the document image in the scan image, (2) a first document image pixel and a last document image pixel for the last scan line of the document image in the scan image, (3) a leftmost document image pixel of the document image in the scan image, and (4) a rightmost document image pixel of the document image in the scan image.

Claims19

Dependent claims

A method of determining a skew angle of a document image inside a scan image having a plurality of scan lines of pixels, comprising the steps of:

(A) receiving a scan line of pixels of the scan image;
(B) automatically detecting an edge segment of the document image by
detecting a first/last document image pixel of the scan line of pixels that belongs to the document image without dividing the scan line into a number of multiple-pixel blocks and without any user intervention and input;
(C) if the first/last document image pixel of the scan line continues the edge segment having the first/last document image pixel of previous scan lines of the scan image, then automatically extending the edge segment to the first/last document image pixel of the scan line;
(D) repeating the steps of (A) and (B) until the edge segment cannot be further extended without any user intervention and without requiring that the document image contains text, wherein the edge segment forms an edge of the document image;
(E) determining if the edge segment is longer than a predetermined length value;
(F) determining the skew angle by determining a slope of the edge segment if the edge segment is longer than the predetermined length value.

4 more elements

An apparatus, comprising:

(A) a storage medium;
(B) a computer executable program stored on the storage medium, the computer executable program, when executed, determining a skew angle of a document image inside a scan image having a plurality of scan lines of pixels, wherein the computer executable program comprises
(I) a first set of instructions that receive and examine a scan line of pixels of the scan image;
(II) a second set of instructions that detect an edge segment of the document image by
detecting a first/last document image pixel of the scan line of pixels that belongs to the document image without dividing the scan line into a number of multiple-pixel blocks and without any user intervention and input;
and extending the edge segment having the first/last document image pixel of previous scan lines of the scan image to the first/last document image pixel of the scan line;
wherein the first and second sets of instructions are repeatedly executed until the edge segment cannot be further extended without any user intervention and without requiring that the document image contains text if the first/last document image pixel of the scan line continues the edge segment;
(III) a third set of instructions that determine if the edge segment is longer than a predetermined length value;
(IV) a fourth set of instructions that determine the skew angle by determining a slope of the edge segment if the edge segment is longer than the predetermined length value.

6 more elements

Dependencies are inferred from the claim text.

Image processing system with image cropping and skew correction

Life of this patent

Image processing system with image cropping and skew correction

Life of this patent

Abstract

Claims19