A signal processing apparatus includes first and second processors that read and execute a program, and a memory. The first processor is configured to process plural color signals at one time and output the plural color signals in parallel. The memory is configured to temporarily store the plural color signals output from the first processor. The second processor is configured to sequentially read and process plural color signals processable at one time from the memory. The first and second processors are configured to process the plural color signals in units of bands including plural lines; after completion of processing of a first band, processing of a second band starts; and the first processor is configured to start processing the second band at a time point before completion of processing of the first band by the second processor, and at which color signals of the first band remain in the memory.