简述

在进行腐蚀或膨胀操作时，碰到了这样一个问题：“OpenCV Error: Assertion failed (anchor.inside(Rect(0, 0, ksize.width, ksize.height))) in cv::normalizeAnchor, file C:/buildslave64/win64_amdocl/2_4_PackSlave-win32-vc10-shared/opencv/modules/imgproc/src/precomp.hpp, line 88” 。

问题分析

仔细检测代码，发现在使用erode() 或 dilate()函数时，核参数输入有误。我的调用代码如下：

Mat element = getStructuringElement(MORPH_RECT, Size(2, 2));
erode(src, dst, element);

大家能发现问题是什么吗？核参数为2，这个错误的。细心的朋友应该会发现腐蚀和膨胀函数介绍时，默认核大小为3*3，说明核参数不可以小于3。

morphOp 数学形态学滤波函数， 腐蚀和膨胀就是通过这个函数得到的，我们来看下这个函数的源码：

//_kernel : 形态学滤波的核
//anchor： 锚点再滤波核的位置
//iterations： 迭代次数
static void morphOp( int op, InputArray _src, OutputArray _dst,
                     InputArray _kernel,
                     Point anchor, int iterations,
                     int borderType, const Scalar& borderValue )
{
    Mat src = _src.getMat(), kernel = _kernel.getMat();
    Size ksize = kernel.data ? kernel.size() : Size(3,3);
    anchor = normalizeAnchor(anchor, ksize);
 
    CV_Assert( anchor.inside(Rect(0, 0, ksize.width, ksize.height)) );
 
    _dst.create( src.size(), src.type() );
    Mat dst = _dst.getMat();
 
    if( iterations == 0 || kernel.rows*kernel.cols == 1 )
    {
        src.copyTo(dst);
        return;
    }
 
    if( !kernel.data )
    {
        kernel = getStructuringElement(MORPH_RECT, Size(1+iterations*2,1+iterations*2));
        anchor = Point(iterations, iterations);
        iterations = 1;
    }
    else if( iterations > 1 && countNonZero(kernel) == kernel.rows*kernel.cols )
    {
        anchor = Point(anchor.x*iterations, anchor.y*iterations);
        kernel = getStructuringElement(MORPH_RECT,
                                       Size(ksize.width + (iterations-1)*(ksize.width-1),
                                            ksize.height + (iterations-1)*(ksize.height-1)),
                                       anchor);
        iterations = 1;
    }
 
    int nStripes = 1;
#if defined HAVE_TBB && defined HAVE_TEGRA_OPTIMIZATION    //这里是TBB指令集操作， 如果你的库没有使用tbb  则这句话不会执行
    if (src.data != dst.data && iterations == 1 &&  //NOTE: threads are not used for inplace processing
        (borderType & BORDER_ISOLATED) == 0 && //TODO: check border types
        src.rows >= 64 ) //NOTE: just heuristics
        nStripes = 4;
#endif
 
    parallel_for(BlockedRange(0, nStripes),
                 MorphologyRunner(src, dst, nStripes, iterations, op, kernel, anchor, borderType, borderType, borderValue));
 
    //Ptr<FilterEngine> f = createMorphologyFilter(op, src.type(),
    //                                             kernel, anchor, borderType, borderType, borderValue );
 
    //f->apply( src, dst );
    //for( int i = 1; i < iterations; i++ )
    //    f->apply( dst, dst );
}