Patent ID: 7710620

Claim:
An image forming method performed by an image forming apparatus to form an image on a commercial printing paper with pigmented inks, where an ink amount control process is performed on image data of the image before forming the image, the ink amount control process comprising: a total amount control step of setting by the image forming apparatus a total amount limit used to control a total amount of the pigmented inks per unit area on the commercial printing paper, wherein the total amount limit is determined so that a full color gamut of the image forming apparatus can be reproduced; a color space conversion step of converting by the image forming apparatus an input color signal of the image data into an output color signal having cyan (C), magenta (M), and yellow (Y) values, wherein the total amount of the pigmented inks per unit area on the commercial printing paper is controlled for each hue according to the total amount limit determined in the total amount control step and according to an ink overflow threshold and maximum saturation of said each hue; and a black generation/under color removal step of converting by the image forming apparatus the CMY values into cyan (C), magenta (M), yellow (Y), and black (K) values by adding a black (K) value and decreasing the CMY values so that portions of cyan (C), magenta (M), and yellow (Y) pigmented inks used to form the image are replaced with a black (K) pigmented ink, wherein a maximum under color removal amount, which is a maximum amount of each of the CMY pigmented inks to be replaced with the K pigmented ink, is obtained by the following formulas: (total amount limit)−(maximum amount of black generation)=(total amount of CMY pigmented inks usable) (total amount of CMY pigmented inks usable)/3=(amount of each of CMY pigmented inks usable) (amount limit for each color)−(amount of each of CMY pigmented inks usable)=maximum under color removal amount, wherein the commercial printing paper is composed of a base material and a coating layer on at least one side of the base material; when the commercial printing paper is brought into contact with one of the pigmented inks for 100 ms in an environment of 23° C. and 50% RH, between 2 and 40 ml/m 2 of the one of the pigmented inks is transferred onto the commercial printing paper; and when the commercial printing paper is brought into contact with the one of the pigmented inks for 400 ms in the environment of 23° C. and 50% RH, between 3 and 50 ml/m 2 of the one of the pigmented inks is transferred onto the commercial printing paper.