An image processing apparatus for converting a low-resolution image into a high-resolution image. When a target pixel is located in an edge region, evaluation values relating to similarity between the target pixel and candidate pixels along a proximate line adjacent to the target pixel are calculated. A distribution of the evaluation values along each of the proximate lines by using an approximate function. Based on the value of the approximate function, a corresponding position of the target pixel on each of the proximate lines is calculated. A pixel value of the new pixel based on the pixel value of the target pixel and a distance between the new pixel and the specified line segments.