如何访问三维矩阵元素？

Question

如何通过3维矩阵进行索引？ 我有这段代码，我知道周期内的字符串是错误的。任何建议以正确的方式进行。

Mat frame_; 
    cvtColor(frame, frame_, CV_BGR2HSV); 
    int size[3] = { capture_box_dim*capture_box_count, capture_box_dim, 3}; 
    Mat ROI = Mat::zeros (3, size, frame_.type()); 
    for (int i = 0; i < capture_box_count; i++) 
    { 
     for (int j = i*capture_box_dim, int k = box_pos_y[i], int l = 0, int t = box_pos_x[i]; 
       j < i*capture_box_dim + capture_box_dim 
      && k < box_pos_y[i] + capture_box_dim 
      && l < capture_box_dim 
      && t < box_pos_x[i] + capture_box_dim; 
      j++, k++, l++, t++) 
     { 
      ROI[j][l] = frame_[k][t]; 
     } 
    } 

Answer 1

你的代码和平是复杂的，但据我所知你喜欢知道如何访问一个点的所有数据（即所有3个值）。使用Vec很简单。

Vec3b intensity = img.at<Vec3b>(y, x); 
uchar blue = intensity.val[0]; 
uchar green = intensity.val[1]; 
uchar red = intensity.val[2]; 

访问Mat元素的最佳方式是at<>方法。在您的代码中：

ROI.at<Vec3b>(j,l) = frame_.at<Vec3b>(k,t); 

Vec是Vector类。 Vec之后的数字表示通道数量。例如，如果你有一个RGB图像，你有3个通道。最后一个字符表示类型。最常见的载体是Vec3b。这里定义了类型的向量：

typedef Vec<uchar, 2> Vec2b; 
typedef Vec<uchar, 3> Vec3b; 
typedef Vec<uchar, 4> Vec4b; 

typedef Vec<short, 2> Vec2s; 
typedef Vec<short, 3> Vec3s; 
typedef Vec<short, 4> Vec4s; 

typedef Vec<int, 2> Vec2i; 
typedef Vec<int, 3> Vec3i; 
typedef Vec<int, 4> Vec4i; 

typedef Vec<float, 2> Vec2f; 
typedef Vec<float, 3> Vec3f; 
typedef Vec<float, 4> Vec4f; 
typedef Vec<float, 6> Vec6f; 

typedef Vec<double, 2> Vec2d; 
typedef Vec<double, 3> Vec3d; 
typedef Vec<double, 4> Vec4d; 
typedef Vec<double, 6> Vec6d; 

Answer 2

OpenCV文档是关于3D的说法。 还拥有一个3D直方图的例子：

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; 

    // intialize 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; 
} 

我觉得这是给你的重要的代码行：

hist.at<float>(pix[0]*N/256, pix[1]*N/256, pix[2]*N/256) += 1.f;