1. An apparatus for forming a color image of pixels each having plural color components, wherein a latent image is formed by an image dot for each color component in an imaging unit area for each pixel on an image carrier, each imaging unit area having plural dot forming positions, the apparatus comprising: (a) light generating means for generating pulse-width modulated scanning light to expose the image carrier; (b) image discriminating means for discriminating whether an objective pixel belongs to a halftone image area or a character image area, based on density data obtained from an image density distribution of the objective pixel and of pixels adjoining the objective pixel; (c) means for generating a first reference wave signal having a predetermined cycle and a second reference wave signal having a cycle longer than the predetermined cycle of the first reference wave signal; and (d) means for modulating the dot forming positions of the scanning light in a scanning direction according to said first and second reference wave signals, wherein the image discriminating means selects the second reference wave signal when the objective pixel is discriminated to be a halftone image area, and wherein the image discriminating means selects the first reference wave signal when the objective pixel is discriminated to be a character image area, the first reference wave signal for the objective pixel being shifted, in accordance with the image density distribution, toward a pixel adjoining the objective pixel having an image density more than that of the objective pixel, so as to determine the dot forming position of the image dot within the imaging unit area of the objective pixel.