A processor includes: a first memory configured to store image data including pixel data of a plurality of pixels that are two-dimensionally arranged; a second memory configured to store neighborhood matrix image data including pixel data of a neighborhood matrix; and a format converter that includes (a) a readout circuit configured to read out the image data from the first memory, (b) a padding arithmetic unit configured to receive the read-out image data, select pixel data of the received read-out image data and padding data inserted at periphery of the plurality of pixels in accordance with mask values of a padding mask, and generate the neighborhood matrix image data including the pixel data and the padding data, and (c) a writing circuit configured to write the neighborhood matrix image data to the second memory.