1. A image processing apparatus comprising: a geometric correction memory which stores a pre-calculated geometric matrix specific to an imaging apparatus; an attenuation map memory which stores an attenuation map of a subject to be imaged in the imaging apparatus; a buffer which stores a plurality of lines generated by the imaging apparatus to be reconstructed; a processor which reconstructs the lines into an attenuation corrected image representation of the subject using the lines from the buffer, the attenuation map, and the geometric matrix; and wherein the geometric correction memory includes a look-up table storing pre-calculated geometric matrix values which are calculated for the imaging apparatus during manufacture and are not calculated for each patient.