cv::NAryMatIterator クラス

n-ary multi-dimensional array iterator. [詳解]

#include <mat.hpp>

公開メンバ関数
	NAryMatIterator ()
	the default constructor
	NAryMatIterator (const Mat **arrays, uchar **ptrs, int narrays=-1)
	the full constructor taking arbitrary number of n-dim matrices
	NAryMatIterator (const Mat **arrays, Mat *planes, int narrays=-1)
	the full constructor taking arbitrary number of n-dim matrices
void	init (const Mat **arrays, Mat *planes, uchar **ptrs, int narrays=-1)
	the separate iterator initialization method
NAryMatIterator &	operator++ ()
	proceeds to the next plane of every iterated matrix
NAryMatIterator	operator++ (int)
	proceeds to the next plane of every iterated matrix (postfix increment operator)

公開変数類
const Mat **	arrays
	the iterated arrays
Mat *	planes
	the current planes
uchar **	ptrs
	data pointers
int	narrays
	the number of arrays
size_t	nplanes
	the number of hyper-planes that the iterator steps through
size_t	size
	the size of each segment (in elements)

限定公開変数類
int	iterdepth
size_t	idx

詳解

n-ary multi-dimensional array iterator.

Use the class to implement unary, binary, and, generally, n-ary element-wise operations on multi-dimensional arrays. Some of the arguments of an n-ary function may be continuous arrays, some may be not. It is possible to use conventional MatIterator 's for each array but incrementing all of the iterators after each small operations may be a big overhead. In this case consider using NAryMatIterator to iterate through several matrices simultaneously as long as they have the same geometry (dimensionality and all the dimension sizes are the same). On each iteration it.planes[0], it.planes[1],... will be the slices of the corresponding matrices.

The example below illustrates how you can compute a normalized and threshold 3D color histogram:

void computeNormalizedColorHist(const Mat& image, Mat& hist, int N, double minProb)
{
    const int histSize[] = {N, N, N};
 
    // make sure that the histogram has a proper size and type
    hist.create(3, histSize, CV_32F);
 
    // and clear it
    hist = Scalar(0);
 
    // the loop below assumes that the image
    // is a 8-bit 3-channel. check it.
    CV_Assert(image.type() == CV_8UC3);
    MatConstIterator_<Vec3b> it = image.begin<Vec3b>(),
                             it_end = image.end<Vec3b>();
    for( ; it != it_end; ++it )
    {
        const Vec3b& pix = *it;
        hist.at<float>(pix[0]*N/256, pix[1]*N/256, pix[2]*N/256) += 1.f;
    }
 
    minProb *= image.rows*image.cols;
 
    // initialize iterator (the style is different from STL).
    // after initialization the iterator will contain
    // the number of slices or planes the iterator will go through.
    // it simultaneously increments iterators for several matrices
    // supplied as a null terminated list of pointers
    const Mat* arrays[] = {&hist, 0};
    Mat planes[1];
    NAryMatIterator itNAry(arrays, planes, 1);
    double s = 0;
    // iterate through the matrix. on each iteration
    // itNAry.planes[i] (of type Mat) will be set to the current plane
    // of the i-th n-dim matrix passed to the iterator constructor.
    for(int p = 0; p < itNAry.nplanes; p++, ++itNAry)
    {
        threshold(itNAry.planes[0], itNAry.planes[0], minProb, 0, THRESH_TOZERO);
        s += sum(itNAry.planes[0])[0];
    }
 
    s = 1./s;
    itNAry = NAryMatIterator(arrays, planes, 1);
    for(int p = 0; p < itNAry.nplanes; p++, ++itNAry)
        itNAry.planes[0] *= s;
}

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このクラス詳解は次のファイルから抽出されました:

• mat.hpp