Method and subsystem for identifying document subimages within digital images

A method that identifies a document sub-image within a digital image, the method comprising:

• receiving the digital image;
• identifying contours corresponding to intensity edges within the digital image;
• generating four contour sets that each includes either predominantly vertically oriented or predominantly horizontally oriented contours selected from the identified contours by partitioning the identified contours into a first set of predominantly vertically oriented contours and a second set of predominantly horizontally oriented contours, selecting contours from the first set of predominantly vertically oriented contours to add to right and left contour sets, and selecting contours from the second set of predominantly horizontally oriented contours to add to upper and lower contour sets;
• generating hypotheses, each comprising data that describes a four-sided polygon positioned and oriented with respect to the received digital image, by combining contours selected from each of the right, left, upper, and lower contour sets from the four contour sets;
• scoring the generated hypotheses;
• selecting a hypothesis among the generated hypotheses based on the generated scores;
• and
• storing the selected hypothesis in memory as an indication of boundaries of a document sub-image within the received digital image.

A non-transitory computer-readable medium for identifying a document sub-image within a digital image, the non-transitory computer-readable medium having recorded thereon instructions that when executed by one or more computer processors, perform operations comprising:

• receiving the digital image;
• identifying contours corresponding to intensity edges within the digital image;
• generating four contour sets that each includes either predominantly vertically oriented or predominantly horizontally oriented contours selected from the identified contours by partitioning the identified contours into a first set of predominantly vertically oriented contours and a second set of predominantly horizontally oriented contours, selecting contours from the first set of predominantly vertically oriented contours to add to right and left contour sets, and selecting contours from the second set of predominantly horizontally oriented contours to add to upper and lower contour sets;
• generating hypotheses, each comprising data that describes a four-sided polygon positioned and oriented with respect to the received digital image, by combining contours selected from each of the right, left, upper, and lower contour sets from the four contour sets;
• scoring the generated hypotheses;
• selecting a hypothesis among the generated hypotheses based on the generated scores;
• and
• storing the selected hypothesis in memory as an indication of boundaries of the document sub-image.