1. An image processing method configured to be executed by an image processing apparatus which comprises a plurality of processing blocks, which are connected in series by a common bus in which data and commands are multiplexed, each of the plurality of processing blocks comprising a processor, the image processing method comprising the steps of: splitting multiplexed input, inputted into one of the processing blocks through the common bus, into commands and data; performing image processing on a piece of data in an order corresponding to an inputted order in the one of the processing blocks and outputting the processed piece of data which is a result of the image processing to the common bus; executing a process indicated by a command, which is inputted into the one of the processing blocks after the piece of data is inputted and before the processed piece of data is outputted, upon the processor of the one of the processing blocks; and transferring the command to the common bus to be inputted into a next one of the processing blocks after outputting the processed piece of data.