Image processing apparatus for detecting a noise line based on noise pixels in the shadow region

1. An image processing apparatus comprising:

a processor for

acquiring an input image of a document and a periphery of the document,

extracting first edge pixels from the input image,

detecting a document region based on the first edge pixels,

detecting a shadow region from within a predetermined range outside of the document region,

extracting noise pixels in the shadow region,

detecting the noise pixels, a number of which connected with one another is equal to or more than a predetermined number, as a noise line, and

correcting the document region of the input image based on a detection result of the noise line.

2. The image processing apparatus according to claim 1 , wherein the processor extracts, as the noise pixels, pixels where a difference between a gradient value of the shadow region and a gradient value of the noise pixels is equal to or more than a threshold.

3. The image processing apparatus according to claim 1 , wherein

the processor

acquires device information that indicates arrangement of an imaging device and a light source in a device that generates the input image, and

determines the predetermined range based on the device information.

4. The image processing apparatus according to claim 1 , wherein

the processor

extracts second edge pixels from within the predetermined range,

detects a plurality of line segments based on the second edge pixels, and

detects, as the shadow region, a region within a second predetermined range from each of the plurality of line segments.

5. The image processing apparatus according to claim 1 , wherein

the processor

specifies, in the document region, a noise line region corresponding to a noise line detected in the shadow region,

determines whether the noise line region overlaps a content based on a difference between a gradient value of the noise line region and a gradient value of peripheral pixels of the noise line region, and

changes a method of correcting the noise line region according to a result of the determining whether the noise line region overlaps a content.

6. The image processing apparatus according to claim 5 , wherein the processor corrects the noise line region based on the peripheral pixels of the noise line region when the processor determines that the noise line region does not overlap a content.

7. The image processing apparatus according to claim 5 , wherein

when the processor determines that the noise line region overlaps a content, the processor further determines whether the content is a character,

when the processor determines that the content is not a character, the processor does not correct the noise line region, and

when the processor determines that the content is a character, the processor corrects the noise line region.

8. The image processing apparatus according to claim 7 , wherein when the processor determines that the content is a character, the processor estimates a character overlapping the noise line region from a context of the content and corrects the noise line region based on the estimated character.

9. A control method of an image processing apparatus, the method comprising:

acquiring an input image of a document and a periphery of the document;

extracting first edge pixels from the input image;

detecting a document region based on the first edge pixels;

detecting a shadow region from within a predetermined range outside of the document region;

extracting noise pixels in the shadow region;

detecting the noise pixels, a number of which connected with one another is equal to or more than a predetermined number, as a noise line; and

correcting the document region of the input image based on a detection result of the noise line.

10. A computer-readable, non-transitory medium storing a computer program, wherein the computer program causes an image processing apparatus to execute a process, the process comprising:

acquiring an input image of a document and a periphery of the document;

extracting first edge pixels from the input image;

detecting a document region based on the first edge pixels;

detecting a shadow region from within a predetermined range outside of the document region;

extracting noise pixels in the shadow region;

detecting the noise pixels, a number of which connected with one another is equal to or more than a predetermined number, as a noise line; and

correcting the document region of the input image based on a detection result of the noise line.