All the images in the database are divided into a number of image groups based on {TAIL ~ the image characteristic index} of each image in the database and the CAD scheme is optimized for {HEAD ~ each image group} 
All the images in the database are divided into a number of image groups based on { TAIL ~ the image characteristic index } of each image in the database and the CAD scheme is optimized for { HEAD ~ each image group }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD