Patent ID: 8014689

Claim:
An image forming apparatus configured to control the density of an output image based on an inherent gamma characteristic of the image forming apparatus which comprises: a patch image forming unit that forms a plurality of patch images having multiple gradation values on a specific medium; a measuring unit that measures the density or lightness of each of the patch images formed on the medium; a sample point arrangement unit that arranges sample points representative of measured density or lightness values in a descending or ascending order of the gradation values; an inflection point region detecting unit that detects any specific inflection point region from among regions defined between the consecutively arranged sample points; a straight line region detecting unit that detects any specific straight line region from among the regions defined between the consecutively arranged sample points; an interpolating operation unit that performs interpolating operation by adding and/or deleting a specific sample point depending on whether (i) an inflection point region is detected among regions defined by four consecutively arranged sample points S n to S n+3 , (ii) a straight line region is detected among regions defined by four consecutively arranged sample points S n to S n+3 , or (iii) neither an inflection point region nor a straight line region is detected among regions defined by four consecutively arranged sample points S n to S n+3 ; (i) in case the above condition (i) is met, (ia) the interpolating operation unit adds a midpoint of a line segment S n+1 S n+2 as a new sample point and deletes the sample points S n+1 and S n+2 ; or (ib) the interpolating operation unit adds a center of gravity of a triangle formed by the sample points S n , S n+1 , and S n+2 and a center of gravity of a triangle formed by the sample points S n+1 , S n+2 and S n+3 as new sample points and deletes the sample points S n+1 and S n+2 ; (ii) in case the above condition (ii) is met, the interpolating operation unit adds the midpoint of the line segment S n+1 S n+2 as a new sample point; (iii) in case that the above condition (iii) is met, the interpolating operation unit adds a center of gravity of a triangle formed by the sample points S n+1 and S n+2 and an intersection point of a straight line containing a line segment S n S n+1 and a straight line containing a line segment S +2 S n+3 as a new sample point, or the interpolating operation unit adds an incenter of a triangle formed by the sample points S n+1 and S n+2 and an intersection point of a straight line containing a line segment S n S n+1 and a straight line containing a line segment S n+2 S n+3 as a new sample point; a characteristic acquisition unit that acquires a gradation characteristic by the interpolating operation; and a characteristic correction unit that corrects the gamma characteristic based on the acquired gradation characteristic.