Optical writer, image forming apparatus, and method of controlling optical writer

An optical writer configured to form an electrostatic latent image on a photosensitive body by emitting a light beam onto the photosensitive body, the optical writer comprising:

• a light source configured to emit the light beam;
• a scanning part configured to guide the emitted light beam onto the photosensitive body and cause the light beam to perform scanning thereon;
• an image information obtaining part configured to obtain image information of an image to be formed as the electrostatic latent image;
• a dithering information obtaining part configured to obtain dithering information of dithering of the image;
• a pixel clock generating part configured to generate a pixel clock signal;
• and
• a light emission control part configured to control the light source based on the obtained image information in accordance with the generated pixel clock signal so as to cause the light source to emit the light beam,
• wherein the pixel clock generating part is configured to modulate a clock frequency of the pixel clock signal in accordance with phase shift information for correcting a change in a speed of the scanning by the light beam on main scanning lines on the photosensitive body, and to determine a timing of modulating the clock frequency based on the obtained dithering information on a main scanning line basis so that the timing of modulating the clock frequency differs between the main scanning lines.