opencv/cxcore.go
func (img *IplImage) SetCOI(coi int) {
	C.cvSetImageCOI((*C.IplImage)(img), C.int(coi))
}
func (img *IplImage) SetCOI(coi int) {
	C.cvSetImageCOI((*C.IplImage)(img), C.int(coi))
}
/* Sets a Channel Of Interest (only a few functions support COI) -
   use cvCopy to extract the selected channel and/or put it back */