＜OpenCV＞边缘填充

OpenCV边缘填充

1、边缘填充类型

enum cv::BorderTypes
ORDER_CONSTANT				iiiiii|abcdefgh|iiiiiii with some specified i	-常量法，常熟值填充；
BORDER_REPLICATE 			aaaaaa|abcdefgh|hhhhhhh -复制法，复制边缘像素；
BORDER_REFLECT				fedcba|abcdefgh|hgfedcb -反射法 ，反射最边缘的像素；
BORDER_WRAP					cdefgh|abcdefgh|abcdefg -平铺法，让图像反复重复；
BORDER_REFLECT_101 			gfedcb|abcdefgh|gfedcba -101反射法，对反射法进行改进，以最边缘像素为轴
BORDER_TRANSPARENT  		uvwxyz|abcdefgh|ijklmno -在OpenCV4中已经被取消了；
BORDER_REFLECT101  			same as BORDER_REFLECT_101
BORDER_DEFAULT 				same as BORDER_REFLECT_101
BORDER_ISOLATED  			do not look outside of ROI

2、copyMakeBorder算子

void cv::copyMakeBorder(InputArray src, OutputArray dst, int top, int bottom, int left, int right, int borderType, const Scalar & value = Scalar())	

Parameters
src				源图像；
dst				目标图像的类型与src相同，大小为size (src.cols +left+right, src.rows+top+bottom)；
top				顶部像素；
bottom			底部像素；
left			左侧像素；
right			右侧像素；参数指定源图像矩形在每个方向上要外推的像素数。例如，top=1, bottom=1, left=1, right=1意味着需要构建1像素宽的边框。
borderType		边界类型，详情见borderInterpolate；
value			边界值，如果borderType==BORDER_CONSTANT；

该函数将源图像复制到目标图像的中间位置。复制源图像的左侧、右侧、上方和下方的区域将被外推像素填充。

3、borderInterpolate算子

int cv::borderInterpolate(int p, int len, int borderType)

Parameters
p				沿其中一个轴的基于0的外推像素坐标, 可能<0或者>len；
len				数组在对应轴上的长度；
borderType		边界类型，除了BORDER_TRANSPARENT和BORDER_ISOLATED之外的边界类型。当borderType==BORDER_CONSTANT时，无论p和len如何，函数总是返回-1；

计算外推像素的源位置。当使用指定的外推边界模式时，该函数计算并返回与指定的外推像素对应的供体像素的坐标。

OpenCV4.5源码分析

主接口函数

void cv::copyMakeBorder( InputArray _src, OutputArray _dst, int top, int bottom,
                         int left, int right, int borderType, const Scalar& value )
{
    CV_INSTRUMENT_REGION();

    CV_Assert( top >= 0 && bottom >= 0 && left >= 0 && right >= 0 && _src.dims() <= 2);

    CV_OCL_RUN(_dst.isUMat(),
               ocl_copyMakeBorder(_src, _dst, top, bottom, left, right, borderType, value))

    Mat src = _src.getMat();
    int type = src.type();

    if( src.isSubmatrix() && (borderType & BORDER_ISOLATED) == 0 )
    {
        Size wholeSize;
        Point ofs;
        src.locateROI(wholeSize, ofs);
        int dtop = std::min(ofs.y, top);
        int dbottom = std::min(wholeSize.height - src.rows - ofs.y, bottom);
        int dleft = std::min(ofs.x, left);
        int dright = std::min(wholeSize.width - src.cols - ofs.x, right);
        src.adjustROI(dtop, dbottom, dleft, dright);
        top -= dtop;
        left -= dleft;
        bottom -= dbottom;
        right -= dright;
    }

    _dst.create( src.rows + top + bottom, src.cols + left + right, type );
    Mat dst = _dst.getMat();

    if(top == 0 && left == 0 && bottom == 0 && right == 0)
    {
        if(src.data != dst.data || src.step != dst.step)
            src.copyTo(dst);
        return;
    }

    borderType &= ~BORDER_ISOLATED;

    CV_IPP_RUN_FAST(ipp_copyMakeBorder(src, dst, top, bottom, left, right, borderType, value))

	//开始填充
    if( borderType != BORDER_CONSTANT )
        copyMakeBorder_8u( src.ptr(), src.step, src.size(),
                           dst.ptr(), dst.step, dst.size(),
                           top, left, (int)src.elemSize(), borderType );
    else
    {
        int cn = src.channels(), cn1 = cn;
        AutoBuffer<double> buf(cn);
        if( cn > 4 )
        {
            CV_Assert( value[0] == value[1] && value[0] == value[2] && value[0] == value[3] );
            cn1 = 1;
        }
        scalarToRawData(value, buf.data(), CV_MAKETYPE(src.depth(), cn1), cn);
        copyMakeConstBorder_8u( src.ptr(), src.step, src.size(),
                                dst.ptr(), dst.step, dst.size(),
                                top, left, (int)src.elemSize(), (uchar*)buf.data() );
    }
}

内部填充函数

具体流程：先填充左右两侧，再填充上下两侧；

void copyMakeBorder_8u( const uchar* src, size_t srcstep, cv::Size srcroi,
                        uchar* dst, size_t dststep, cv::Size dstroi,
                        int top, int left, int cn, int borderType )
{
    const int isz = (int)sizeof(int);
    int i, j, k, elemSize = 1;
    bool intMode = false;

    if( (cn | srcstep | dststep | (size_t)src | (size_t)dst) % isz == 0 )
    {
        cn /= isz;
        elemSize = isz;
        intMode = true;
    }

    cv::AutoBuffer<int> _tab((dstroi.width - srcroi.width)*cn);
    int* tab = _tab.data();
    int right = dstroi.width - srcroi.width - left;
    int bottom = dstroi.height - srcroi.height - top;

    // 左侧位置计算
    for( i = 0; i < left; i++ )
    {
        j = cv::borderInterpolate(i - left, srcroi.width, borderType)*cn;
        for( k = 0; k < cn; k++ )
            tab[i*cn + k] = j + k;
    }

    // 右侧位置计算
    for( i = 0; i < right; i++ )
    {
        j = cv::borderInterpolate(srcroi.width + i, srcroi.width, borderType)*cn;
        for( k = 0; k < cn; k++ )
            tab[(i+left)*cn + k] = j + k;
    }

    srcroi.width *= cn;
    dstroi.width *= cn;
    left *= cn;
    right *= cn;

    uchar* dstInner = dst + dststep*top + left*elemSize;

    // 填充
    for( i = 0; i < srcroi.height; i++, dstInner += dststep, src += srcstep )
    {
        if( dstInner != src )
            memcpy(dstInner, src, srcroi.width*elemSize);

        if( intMode )
        {
            const int* isrc = (int*)src;
            int* idstInner = (int*)dstInner;
            for( j = 0; j < left; j++ )
                idstInner[j - left] = isrc[tab[j]];
            for( j = 0; j < right; j++ )
                idstInner[j + srcroi.width] = isrc[tab[j + left]];
        }
        else
        {
            for( j = 0; j < left; j++ )
                dstInner[j - left] = src[tab[j]];
            for( j = 0; j < right; j++ )
                dstInner[j + srcroi.width] = src[tab[j + left]];
        }
    }

    dstroi.width *= elemSize;
    dst += dststep*top;

    // 顶部位置计算并填充
    for( i = 0; i < top; i++ )
    {
        j = cv::borderInterpolate(i - top, srcroi.height, borderType);
        memcpy(dst + (i - top)*dststep, dst + j*dststep, dstroi.width);
    }

    // 底部位置计算并填充
    for( i = 0; i < bottom; i++ )
    {
        j = cv::borderInterpolate(i + srcroi.height, srcroi.height, borderType);
        memcpy(dst + (i + srcroi.height)*dststep, dst + j*dststep, dstroi.width);
    }
}

//常量填充
void copyMakeConstBorder_8u( const uchar* src, size_t srcstep, cv::Size srcroi,
                             uchar* dst, size_t dststep, cv::Size dstroi,
                             int top, int left, int cn, const uchar* value )
{
    int i, j;
    cv::AutoBuffer<uchar> _constBuf(dstroi.width*cn);
    uchar* constBuf = _constBuf.data();
    int right = dstroi.width - srcroi.width - left;
    int bottom = dstroi.height - srcroi.height - top;

    for( i = 0; i < dstroi.width; i++ )
    {
        for( j = 0; j < cn; j++ )
            constBuf[i*cn + j] = value[j];
    }

    srcroi.width *= cn;
    dstroi.width *= cn;
    left *= cn;
    right *= cn;

    uchar* dstInner = dst + dststep*top + left;

    for( i = 0; i < srcroi.height; i++, dstInner += dststep, src += srcstep )
    {
        if( dstInner != src )
            memcpy( dstInner, src, srcroi.width );
        memcpy( dstInner - left, constBuf, left );
        memcpy( dstInner + srcroi.width, constBuf, right );
    }

    dst += dststep*top;

    for( i = 0; i < top; i++ )
        memcpy(dst + (i - top)*dststep, constBuf, dstroi.width);

    for( i = 0; i < bottom; i++ )
        memcpy(dst + (i + srcroi.height)*dststep, constBuf, dstroi.width);
}

计算外推像素的源位置函数

/*
 Various border types, image boundaries are denoted with '|'

 * BORDER_REPLICATE:     aaaaaa|abcdefgh|hhhhhhh
 * BORDER_REFLECT:       fedcba|abcdefgh|hgfedcb
 * BORDER_REFLECT_101:   gfedcb|abcdefgh|gfedcba
 * BORDER_WRAP:          cdefgh|abcdefgh|abcdefg
 * BORDER_CONSTANT:      iiiiii|abcdefgh|iiiiiii  with some specified 'i'
 */
int cv::borderInterpolate( int p, int len, int borderType )
{
    CV_TRACE_FUNCTION_VERBOSE();

    CV_DbgAssert(len > 0);

#ifdef CV_STATIC_ANALYSIS
    if(p >= 0 && p < len)
#else
    if( (unsigned)p < (unsigned)len )
#endif
        ;
    else if( borderType == BORDER_REPLICATE )
        p = p < 0 ? 0 : len - 1;
    else if( borderType == BORDER_REFLECT || borderType == BORDER_REFLECT_101 )
    {
        int delta = borderType == BORDER_REFLECT_101;
        if( len == 1 )
            return 0;
        do
        {
            if( p < 0 )
                p = -p - 1 + delta;
            else
                p = len - 1 - (p - len) - delta;
        }
#ifdef CV_STATIC_ANALYSIS
        while(p < 0 || p >= len);
#else
        while( (unsigned)p >= (unsigned)len );
#endif
    }
    else if( borderType == BORDER_WRAP )
    {
        CV_Assert(len > 0);
        if( p < 0 )
            p -= ((p-len+1)/len)*len;
        if( p >= len )
            p %= len;
    }
    else if( borderType == BORDER_CONSTANT )
        p = -1;
    else
        CV_Error( CV_StsBadArg, "Unknown/unsupported border type" );
    return p;
}

＜OpenCV＞ 边缘填充

OpenCV边缘填充

OpenCV4.5源码分析

＜OpenCV＞边缘填充