Method of transferring information indicating reflecting surface of rotating polygonal mirror

An image forming apparatus comprising:

• a first controller configured to transmit a main scanning synchronization signal, and
• a second controller configured to output image data triggered by the main scanning synchronization signal,
• wherein the first controller specifies a reference reflection surface in a plurality of reflecting surfaces that a rotating polygonal mirror comprises, and transmits to the second controller a main scanning synchronization signal having a first waveform that does not correspond to the reference reflection surface and a second waveform which is a waveform that does correspond to the reference reflection surface and is different to the first waveform.

A controller that generates image data that becomes a basis for an image formed by a scanning apparatus having a light source, a plurality of reflecting surfaces, a rotating polygonal mirror that deflects light outputted from the light source while rotating, and a detection unit that outputs a first signal in accordance with detecting the light deflected by the rotating polygonal mirror, the controller comprising:

• a reception unit configured to receive a second signal, which is a main scanning synchronization signal for controlling a write start in a main scanning direction and which is generated, based on the first signal, in another controller that controls the scanning apparatus by a reference reflection surface out of the plurality of reflecting surfaces being specified, the second signal having a first waveform that does not correspond to the reference reflection surface and a second waveform which is a waveform that does correspond to the reference reflection surface and is different to the first waveform;
• and
• an extraction unit configured to extract information indicating the reference reflection surface from the second signal.