Image forming apparatus, method of controlling the same, computer product, and process cartridge

In an image forming apparatus, a pattern forming unit forms a pattern for correcting image positional displacement, and a detecting unit (A, B) detects the pattern. A correcting unit (230) corrects an image positional displacement based on the pattern detected. If the pattern cannot be detected, then monochrome printing is enabled, and a notifying unit (231) notifies that the correction is not possible.