今天简单来看一下OpenCV中的边界填充

@param src Source image.
@param dst Destination image of the same type as src and the size Size(src.cols+left+right,
src.rows+top+bottom) .
@param top the top pixels
@param bottom the bottom pixels
@param left the left pixels
@param right Parameter specifying how many pixels in each direction from the source image rectangle
to extrapolate. For example, top=1, bottom=1, left=1, right=1 mean that 1 pixel-wide border needs
to be built.
@param borderType Border type. See borderInterpolate for details.
@param value Border value if borderType==BORDER_CONSTANT .

@sa  borderInterpolate
*/
CV_EXPORTS_W void copyMakeBorder(InputArray src, OutputArray dst,
                                 int top, int bottom, int left, int right,
                                 int borderType, const Scalar& value = Scalar() );

这里的核心就是理解borderType，具体就是

enum BorderTypes {
    BORDER_CONSTANT    = 0, //!< `iiiiii|abcdefgh|iiiiiii`  with some specified `i`
    BORDER_REPLICATE   = 1, //!< `aaaaaa|abcdefgh|hhhhhhh`
    BORDER_REFLECT     = 2, //!< `fedcba|abcdefgh|hgfedcb`
    BORDER_WRAP        = 3, //!< `cdefgh|abcdefgh|abcdefg`
    BORDER_REFLECT_101 = 4, //!< `gfedcb|abcdefgh|gfedcba`
    BORDER_TRANSPARENT = 5, //!< `uvwxyz|abcdefgh|ijklmno`

    BORDER_REFLECT101  = BORDER_REFLECT_101, //!< same as BORDER_REFLECT_101
    BORDER_DEFAULT     = BORDER_REFLECT_101, //!< same as BORDER_REFLECT_101
    BORDER_ISOLATED    = 16 //!< do not look outside of ROI
};

具体的理解：

其实不用记，实验一下就了解

发现两个问题：

1. 图像宽度不为4的倍数时，画出会有错位现象
2. 选择的颜色，B与R通道反了
   这些问题，OpenCV肯定是不会改的，那就自己处理一下。