Image region detection method, recording medium, and device therefor

A recording medium that records an image region detection program for causing a computer to execute a process for detecting a quadrangular region on a second image, the second image being obtained by photographing a quadrangular first image and the second image including the quadrangular region that is an image region corresponding to the first image, comprising:

• a transition point detection process for detecting one pixel, as a transition point, when a difference in pixel values between adjacent pixels exceeds a threshold value while scanning toward a periphery of the second image from a plurality of pixels set as initial points positioned within a certain range from a center of the second image;
• a four-sides-candidates detection process for creating sides of a quadrangle in respective combinations on the basis of transition points on the assumption that there is a combination of transition points obtained in a one-by-one manner from respective transition point detection lines that are oriented in the same direction and that are members of a group of transition point detection lines that are based on the transition point detection performed in four directions on the second image, the four directions being the two vertical and the two horizontal directions, and detecting as candidates for sides of the quadrangle, from among the sides created in the respective directions, those sides that are closest to the initial points;
• and
• a side redetection control process for determining, on the basis of a quadrangle formed by the four candidate sides that have been detected, whether or not a detected side has been detected falsely, and performing redetection of candidates for sides when the side is confirmed to be a side that has been detected falsely.

An image region detection device for detecting a quadrangular region in a second image, the second image being obtained by photographing a quadrangular first image, and the second image including the quadrangular region that is an image region corresponding to the first image, comprising:

• a transition point detection unit for detecting one pixel, as a transition point, when a difference in pixel values between adjacent pixels exceeds a threshold value while scanning toward a periphery of the second image from a plurality of pixels set as initial points positioned within a certain range from a center of the second image;
• a four-sides-candidates detection unit for creating sides of a quadrangle in respective combinations on the basis of transition points on the assumption that there is a combination of transition points obtained in a one-by-one manner from respective transition point detection lines that are oriented in the same direction and that are members of a group of transition point detection lines that are based on the transition point detection performed in four directions on the second image, the four directions being the two vertical and the two horizontal directions, and detecting as candidates for sides of the quadrangle, from among the sides created in the respective directions, those sides that are closest to the initial points;
• and
• a side redetection control unit for determining, on the basis of a quadrangle formed by the four candidate sides that have been detected, whether or not a detected side is a side that has been detected falsely, and performing redetection of candidates for sides when the side is confirmed to be a side that has been detected falsely.