1. A non-transitory, computer-readable recording medium storing therein an image conversion program that causes a computer to execute a process comprising: extracting, among pixel rows parallel to an object pixel row in an image to be converted, a first pixel row overlapping a region formed of a pixel group within a predetermined range from an given pixel of the object pixel row and a second pixel row having a number of pixels successively overlapping the region equal to or greater than that of the first pixel row; acquiring a pixel count from a pixel at an end in a given direction that is any one among a scanning direction of the object pixel row and a direction opposite to the scanning direction, in a first pixel group included in the region in the extracted first pixel row, to a first pixel included in the first pixel group; identifying a second pixel at a position advanced by the acquired pixel count in a direction opposite to the given direction from the pixel at the end in the given direction in a second pixel group included in the region in the extracted second pixel row; and calculating a value of the second pixel in a case of converting an original image by referring to a storage device that stores therein a value of the first pixel in the case of converting the image.