1. An image processing apparatus comprising: a memory; a first conversion unit operable to perform a first conversion of an image represented by span information, by dividing, using the memory, the span information by a predetermined width into a plurality of pieces of span information; a second conversion unit operable to perform, using the memory, a second conversion of the image represented by pixel information, by dividing, using the memory, the pixel information by the predetermined width into a plurality of pieces of pixel information; and a control unit configured to determine, by comparing a first amount corresponding to a usage amount of the memory used for the first conversion with a second amount corresponding to a usage amount of the memory used for the second conversion, which of the first conversion and the second conversion requires less usage amount of the memory, cause the first conversion unit to perform the first conversion of the image if it is determined the first conversion requires less usage amount of the memory than the second conversion, and cause the second conversion unit to perform the second conversion of the image if it is determined the second conversion requires less usage amount of memory than the first conversion.