opencv/cxcore.go
func SubScalar(src *IplImage, value Scalar, dst *IplImage) {
	SubScalarWithMask(src, value, dst, nil)
}
func SubScalar(src *IplImage, value Scalar, dst *IplImage) {
	SubScalarWithMask(src, value, dst, nil)
}
// Calculates the per-element difference between an array and a scalar.
//   dst = src - value