1. A computer implemented method of processing optical coherence tomography (OCT) image data, the OCT image data comprising a plurality of cross sectional images of a subject, the cross sectional images each comprising a plurality of scan lines obtained by measuring the time delay of light reflected, in a depth direction, from optical interfaces within the subject, the method comprising aligning the cross sectional images by determining relative translations for each cross sectional image in the depth direction and in a lateral direction, perpendicular to the depth direction, to form a set of aligned cross sectional images; aligning image patches of the aligned cross sectional images, each image patch comprising at least one scan line, by determining relative translations for each patch in the depth direction to form a set of aligned patches; forming an image matrix from the aligned patches; and applying matrix completion to the image matrix to obtain a reduced speckle noise image of the subject.