1. An image forming apparatus, comprising: an image carrier; an exposure unit configured to emit light for exposure onto said image carrier according to image data; a discrimination unit configured to discriminate a low density area in which density levels of all items of image data in such low density area are less than a predetermined density; and a control unit configured to control a light emitting intensity of said exposure unit for each pixel in the low density area discriminated by said discrimination unit, wherein in a pixel area of N×M pixels (N and M are integers) in the low density area, said control unit determines a pixel of interest in the pixel area, sets a density level of the pixel of interest to a density level based on the density levels of all pixels included in the pixel area, sets a light emitting intensity for the pixel of interest to a first light emitting intensity which is more than a predetermined intensity, and sets light emitting intensities for pixels other than the pixel of interest to light emitting intensities which are less than the predetermined intensity.