Patent ID: 7623148

Claim:
An optical scanning apparatus for irradiating an image carrier with a light beam emitted from a light source, comprising: an approximation formula determination unit which determines an nth-order approximation formula and an mth-order approximation formula (where n and m are natural numbers and m>n holds), which represent the sensitivity characteristic of the image carrier along the main-scanning direction thereof, from sensitivity data representing the sensitivity of each area obtained by dividing the surface of the image carrier into a plurality of areas; a sensitivity correction value determination unit which determines a sensitivity correction value, which is a correction value of sensitivity in each area, from the nth-order approximation formula and mth-order approximation formula; and a bias current controller which controls a bias current, which is applied to the light source, in accordance with the sensitivity correction values, wherein the surface of the image carrier is divided into P-number of columns in the main-scanning direction and Q-number of rows in the sub-scanning direction, thereby dividing the surface into a total of P×Q areas; said approximation formula determination unit includes a part which, with regard to each row of the Q-number of rows, determines the nth-order approximation formula and the mth-order approximation formula from each item of sensitivity data of P-number of areas along the main-scanning direction; and said sensitivity correction value determination unit includes: a part which, with regard to each area, calculates a difference value between the corresponding nth-order approximation formula and the mth-order approximation formula; a part which, with regard to each column of the P-number of columns, calculates an average value of the difference values regarding Q-number of areas belonging to each column; a part which determines the mth-order approximation formula from the calculated P-number of average values and calculates a first maximum value from the mth-order approximation formula determined; a part which divides the sensitivity data of each area by the respective first maximum value, thereby calculating a correction coefficient in the main-scanning direction; a part which, with regard to each row of the Q-number of rows, calculates a second maximum value from the corresponding nth-order approximation formula; a part which divides the sensitivity data of each area by the respective second maximum value, thereby calculating a correction coefficient in the sub-scanning direction; and a part which, with regard to each area, adds the correction coefficient in the main-scanning direction and the correction coefficient in the sub-scanning direction, thereby calculating the sensitivity correction value.