PCACompute() 不触及 Matrix<> 输出数组参数

Question

我正在将 EmguCV 3.0.0 包装器用于 OpenCV 3.0。 EmguCV PCACompute method wraps the OpenCV PCA::operator() 方法。

以下代码编译运行。评论应该很好地解释意图。

// Populate the 5 row by 8 column input array (5 samples of 8 dimensions).
// The sample dimensions (columns) vary like this:
//   - low variance: 0, 1, 4, 5, 6, 7
//   - high variance: 2, 3
Matrix<double> input = new Matrix<double>(5, 8);
var r = new Random();
for (int row = 0; row < 5; row++) {
    input.Data[row,0] = r.Next(0, 10);     // low variance
    input.Data[row,1] = r.Next(0, 20);     // low variance
    input.Data[row,2] = r.Next(80, 210);   // high variance
    input.Data[row,3] = r.Next(0, 240);    // highest variance
    input.Data[row,4] = r.Next(20, 21);    // very low variance
    input.Data[row,5] = r.Next(0, 10);     // low variance
    input.Data[row,6] = r.Next(0, 10);     // low variance
    input.Data[row,7] = r.Next(200, 210);  // low variance
}

// create output array for PCACompute()
var eigenvectors = new Matrix<double>(8, 8);

// create *empty* mean array so that PCACompute() calculates its own means
var means = new Mat();

// HERE IS THE MAGIC.
CvInvoke.PCACompute(input, means, eigenvectors);

但是魔法坏了。 eigenvectors 毕竟是全零。这个漂亮的打印代码：

// print each eigenvector on its own line
for (int vectorIdx = 0; vectorIdx < eigenvectors.Rows; vectorIdx++) {
    string vectorStr = "";
    for(int dimension = 0; dimension < eigenvectors.Cols; dimension++) {
        vectorStr += eigenvectors.Data[vectorIdx, dimension].ToString() + ", ";
    }
    Console.WriteLine("{ " + vectorStr.Substring(0, vectorStr.Length - 2) + " }");
}

给出此输出：

{ 0, 0, 0, 0, 0, 0, 0, 0 }
{ 0, 0, 0, 0, 0, 0, 0, 0 }
{ 0, 0, 0, 0, 0, 0, 0, 0 }
{ 0, 0, 0, 0, 0, 0, 0, 0 }
{ 0, 0, 0, 0, 0, 0, 0, 0 }
{ 0, 0, 0, 0, 0, 0, 0, 0 }
{ 0, 0, 0, 0, 0, 0, 0, 0 }
{ 0, 0, 0, 0, 0, 0, 0, 0 }

事实上，如果我在 eigenvectors 之前设置一个成员，然后 将其传递给 PCACompute:

eigenvectors.Data[1,1] = 42;

CvInvoke.PCACompute(input, means, eigenvectors);

漂亮的印刷品显示 eigenvectors 完全没有被 PCACompute 影响：

{ 0, 0, 0, 0, 0, 0, 0, 0 }
{ 0, 42, 0, 0, 0, 0, 0, 0 }
{ 0, 0, 0, 0, 0, 0, 0, 0 }
{ 0, 0, 0, 0, 0, 0, 0, 0 }
{ 0, 0, 0, 0, 0, 0, 0, 0 }
{ 0, 0, 0, 0, 0, 0, 0, 0 }
{ 0, 0, 0, 0, 0, 0, 0, 0 }
{ 0, 0, 0, 0, 0, 0, 0, 0 }

这是一个错误，还是我做错了？

Answer 1

尽管根据类型系统是兼容的，但传递给 PCACompute 的第三个参数不能是 Matrix<> 类型。不过，如果它是 Mat 类型，则一切正常！

Matrix<double> input = new Matrix<double>(5, 8);
var r = new Random();
for (int row = 0; row < 5; row++) {
    input.Data[row,0] = r.Next(0, 10);     // low variance
    input.Data[row,1] = r.Next(0, 20);     // low variance
    input.Data[row,2] = r.Next(80, 210);   // high variance
    input.Data[row,3] = r.Next(0, 240);    // highest variance
    input.Data[row,4] = r.Next(20, 21);    // very low variance
    input.Data[row,5] = r.Next(0, 10);     // low variance
    input.Data[row,6] = r.Next(0, 10);     // low variance
    input.Data[row,7] = r.Next(200, 210);  // low variance
}

// CHANGE HERE
// Matrix<> was not changed by PCACompute(), so change eigenvectors to a Mat
var eigenvectors = new Mat(8, 8, DepthType.Cv64F, 1);

// create *empty* mean array so that PCACompute() calculates its own means
var means = new Mat();

// Now the magic works fine.
CvInvoke.PCACompute(input, means, eigenvectors);

现在 eigenvectors 包含更合理的数据（尽管它在漂亮的打印函数中使用不同的访问代码）

 > eigenvectors.GetValueRange().Max
0.999418
 > eigenvectors.GetValueRange().Min
-0.6326281

PCACompute() 不触及 Matrix<> 输出数组参数

PCACompute() does not touch the Matrix<> ouput array parameter

c#

opencv

emgucv