Image forming apparatus performing halftone processing shifting scan line start position in main-scan direction when scan lines are shifted in sub-scan direction relative to target

An image forming apparatus, comprising:

• a photosensitive body;
• a scanning unit configured to form an electrostatic latent image using a plurality of scan lines on the photosensitive body by, on a basis of an image signal, performing scanning of the photosensitive body in a main scan direction using one or more scanning beams repeatedly in a sub-scan direction orthogonal to the main scan direction;
• a generating unit configured to perform halftone processing on image data and generate the image signal;
• and
• a storing unit configured to store start position information indicating start positions in the main scan direction of the plurality of scan lines,
• wherein, in a case where an interval between the plurality of scan lines formed by the scanning unit is shifted such that, with a period of N consecutive intervals along the sub-scan direction, (N−1) consecutive intervals from among the N intervals is a first interval and a remaining one interval is a second interval different from the first interval, the start position information indicates to linearly shift the start positions of N scan lines forming the (N−1) intervals in the main scan direction along the sub-scan direction.