Multi-beam drawing method using partially damaged light emitting devices and including spiral correction

A scanning method performed, comprising:

• providing an object to be scanned which is rotatable around a rotating axis and having a cylindrical shape;
• providing rotating means for rotating said object to be scanned;
• providing a plurality of light-emitting devices arranged in a line and simultaneously applying a plurality of beams emitted therefrom onto said object to be scanned;
• providing image data supply means for supplying image data to said plurality of light-emitting devices;
• providing sub-scanning means for moving said plurality of light-emitting devices in a sub-scanning direction which is parallel to the rotating axis of said object to be scanned so that said plurality of light-emitting devices scan a surface of said object to be scanned in a spiral fashion;
• detecting damage to any of said light-emitting devices;
• selecting at least one of a plurality of partial light-emitting device lines obtained by partitioning said light-emitting device line at a damaged light-emitting device;
• processing image data of a rectangular Wage by dividing said image data into image data of a plurality of virtual small images parallel to the sub-scanning direction based on the number of light-emitting devices included in said partial light-emitting device line and sequentially shifting the plurality of virtual small images in a reverse direction to the sub-scannig direction in accordance with positions of the plurality of virtual small images in a main scanning direction;
• and
• scanning with the partial light-emitting device line selected in said selecting step based on the image data processed in said image data processing step.