1. An image forming apparatus comprising: an image carrier; an exposing unit configured to form an electrostatic latent image including dot images based on image data, by exposing a surface of the image carrier with exposure energy in accordance with pixels in the image data, wherein each of the dot images corresponds to one of the pixels; and a developing unit configured to perform a developer contact developing method by applying a developing bias onto a developer carrier carrying a non-magnetic one-component developer and causing the non-magnetic one-component developer on the developer carrier to contact the image carrier, thereby developing the electrostatic latent image on the image carrier into a toner image, wherein the image carrier is configured to transfer the toner image onto a recording material; and the developing bias or the exposure energy is configured to be adjusted such that an isolated one-dot image has a predetermined image density, the image forming apparatus further comprising: a control unit configured to control the exposing unit to provide, when the image carrier is exposed to form dot images which are continuously arranged in a sub scanning direction, an exposure time period for each of the continuously arranged dot images shorter than a time period for exposing the image carrier to form an isolated one-dot image, and among the continuously arranged dot images an exposure time period for an inner dot image positioned in between adjacent dot images is shorter than that for each of the adjacent dot images.