| 摘要 |
PROBLEM TO BE SOLVED: To prevent color shift at the time of forming a full color image due to shift of the writing position of a black image and to enhance productivity of monochromatic image. SOLUTION: At the time of forming a monochromatic image, the number of sheets being outputted per unit time is increased as compared with that at the time of forming a full color image by using more than one beam for writing in a light source unit 53 for black image. At the time of forming a full color image, only one light beam is emitted from the light source unit 53 and the pixel density position of light spot of that light beam is controlled, by a light spot position control means B, to a position corresponding to a pixel density predetermined depending on a high image quality mode or a speed preference mode. Consequently, color shift of the black image from the image of other color can be prevented even in such an arrangement as the pixel density position of light spot from the light source unit 53 for black image is switched by a pixel density switching mechanism A.
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