将节点数组（可变长度）转换为 const float** 以调用 opencv.calcHist

Question

上下文

我目前正在 https://github.com/piercus/node-opencv (forked from https://github.com/peterbraden/node-opencv)，我正在为 calcHist 函数实现一个活页夹。

问题

C++ 函数以 const float** ranges 作为输入（参见 http://docs.opencv.org/2.4/modules/imgproc/doc/histograms.html#calchist）
考虑到
我不知道如何在不破坏编译器的情况下有条件地设置这个 const float** 的大小

解决方法

考虑到最大维数为 3，我做了一个解决方法（参见 full source )

// Wrap Javascript input which is like [[0, 256], [0, 256]]
Local<Array> nodeRanges = Local<Array>::Cast(info[3]->ToObject());

// create a first table
float histRanges[dims][2];

for (unsigned int i = 0; i < dims; i++) {
  Local<Array> nodeRange = Local<Array>::Cast(nodeRanges->Get(i)->ToObject());
  float lower = nodeRange->Get(0)->NumberValue();
  float higher = nodeRange->Get(1)->NumberValue();
  histRanges[i][0] = lower;
  histRanges[i][1] = higher;
}

// minimum length is 1 so i can fullfill first range without issue
float first_range[] = { histRanges[0][0], histRanges[0][1] };
float second_range[] = { 0, 0}; // here is my problem, do i really need to do this
float third_range[] = { 0, 0};// same problem here

if(dims >= 2){
  second_range[0] = histRanges[1][0];
  second_range[1] = histRanges[1][1];
}
if(dims >= 3){
  third_range[0] = histRanges[2][0];
  third_range[1] = histRanges[2][1];
}

// now i can create a const float** compatible type 
const float* histRanges1[] = {first_range, second_range, third_range};

[... other stuffs ...]

// const float** is needed here
cv::calcHist(&inputImage, 1, channels, cv::Mat(), outputHist, dims, histSize, histRanges1, uniform);

问题

是否可以在不创建 "zero-filled" 对象的情况下以优雅的方式完成此操作？我希望输入的最大大小为 32（而不是 3）。

Answer 1

您不需要复制 histRanges 的内容，因为其中的数字已经按照 cv::calcHist 的要求排列为 float 数组。您只需要创建一个指向这些数组的指针数组。

float histRanges[dims][2];
const float* ranges[dims];

for (unsigned int i = 0; i < dims; i++) {
  Local<Array> nodeRange = Local<Array>::Cast(nodeRanges->Get(i)->ToObject());
  float lower = nodeRange->Get(0)->NumberValue();
  float higher = nodeRange->Get(1)->NumberValue();
  histRanges[i][0] = lower;
  histRanges[i][1] = higher;
  ranges[i] = histRanges[i];
}

cv::calcHist(&inputImage, 1, channels, cv::Mat(), outputHist, dims, histSize, ranges, uniform);

将节点数组（可变长度）转换为 const float** 以调用 opencv.calcHist

Convert Node Array (variable lenght) to a const float** to call opencv.calcHist

c++

opencv

pointers

constants

node.js-addon

上下文

问题

解决方法

问题