An another way to pad an image is to use copyMakeBorder function:
C++: void copyMakeBorder(InputArray src, OutputArray dst, int top, int bottom, int left, int right, int borderType, const Scalar& value=Scalar() )
Then padding with zeros is simply like that
Mat image,image_pad;
copyMakeBorder(image,image_pad,1,1,1,1,BORDER_CONSTANT,Scalar(0));
Finally, here is the tutorial of Adding borders to your images.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…