To provide an image processor which applies image-processing to received printing data, outputs the processed data to a printing engine, and performs an effective trapping operation without enlarging the size of the processor and lowering the processing speed.

This image processor 2 comprises a front processor 21 for converting the received printing data 1 to bitmap data to store it to a memory 22 and a rear processor 23 that processes the bitmap data stored in the memory 22 corresponding to the driving of the printing engine 3 and outputs the processed data to the printing engine 3. The rear processor 23 has the trapping operation means 25 for performing the trapping operation according to the bitmap data.