Patent ID: 8848248

Claim:
A gradation correction device to instruct a printing apparatus to print an image in which a control strip formed by linearly arranging a plurality of patches having different densities is located at an end portion of a paper sheet; to obtain density data of each patch of the control strip by analyzing read image data obtained by instructing a reading device to read the image on the paper sheet; and to generate gradation correction data in accordance with the density data, which is used in, the printing apparatus, wherein the control strip has white or light-colored end patches arranged at both ends in a longitudinal direction of the control strip, and has at least one reference point at each of both end portions of the control strip in the longitudinal direction, the reference point being defined by two straight lines including a fine line drawn on at least a part of a peripheral edge of each end patch except a border between the end patch and an adjacent patch which is adjacent to the end patch, and wherein the gradation correction device detects the reference point at each of the both end portions of the control strip in the read image data, and obtains the density data of each patch by specifying a position of each patch in the control strip in the read image data in accordance with the detected reference point.