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