优化Mat通道的OR

Question

我想使用这个公式将BGR cv :: Mat转换为灰色Gray=B OR G OR R; pixel-wise operation.我试过这个:

cv::Mat diff_channels[3];
cv::split(diff, diff_channels);
diff = diff_channels[0] | diff_channels[1] | diff_channels[2];

这可以通过更好的方法实现吗？

另外,如果我想实现Gray=MAX(B,G,R); pixel-wise operation任何建议？

Answer 1

您可以使用cv::ParallelLoopBodywith cv::parallel_for_来使用OpenCV Concurrency API:

class ParallelBGRtoGrayOR : public ParallelLoopBody
{
    const Mat3b src;
    mutable Mat1b dst;

public:
    ParallelBGRtoGrayOR(const Mat3b& _src, Mat1b& _dst) : ParallelLoopBody(), src(_src), dst(_dst) {}

    virtual void operator()(const Range& range) const
    {
        int rows = range.end - range.start;
        int cols = src.cols;
        int len = rows * cols;

        const uchar* yS = src.ptr<uchar>(range.start);
        uchar* yD = dst.ptr<uchar>(range.start);

        for (int i = 0; i < len; ++i, yD++, yS += 3)
        {
            *yD = yS[0] | yS[1] | yS[2];
            //*yD = std::max(yS[0], std::max(yS[1], yS[2]));
        }
    }
};

void cvtBgrToGray_OR_Miki(const Mat3b& src, Mat1b& dst)
{
    dst.create(src.rows, src.cols);
    parallel_for_(Range(0, src.rows), ParallelBGRtoGrayOR(src, dst), -1);
}

测试

用你的和@akarsakov方法测试,我得到了(时间以毫秒为单位):

Size:           akarsakov       Humam Helfawi   Miki            OpenCV (not same operation)

[10 x 10]       0.00109963      0.0711094       2.60722         0.0934685
[100 x 100]     0.0106298       0.0373874       0.0461844       0.0395867
[1000 x 1000]   1.1799          3.30622         0.747382        1.61646
[1280 x 720]    1.07324         2.91585         0.520858        0.9893
[1920 x 1080]   2.31252         6.87818         1.11502         1.94011
[4096 x 3112]   14.3454         42.0125         6.79644         12.0754
[10000 x 10000] 115.575         321.145         61.1544         93.8846

注意事项

@akarsakov方法(在原始数据上巧妙地工作)通常是更好的方法,因为它非常快速且更容易编写.使用它ParallelLoopBody只有大图像(至少在我的电脑上)有一些优势.

我假设源图像是连续的.这项检查应该在实践中完成.

测试代码

您可以使用以下代码在PC上评估结果:

#include <opencv2/opencv.hpp>
#include <iostream>
using namespace std;
using namespace cv;

class ParallelBGRtoGrayOR : public ParallelLoopBody
{
    const Mat3b src;
    mutable Mat1b dst;

public:
    ParallelBGRtoGrayOR(const Mat3b& _src, Mat1b& _dst) : ParallelLoopBody(), src(_src), dst(_dst) {}

    virtual void operator()(const Range& range) const
    {
        int rows = range.end - range.start;
        int cols = src.cols;
        int len = rows * cols;

        const uchar* yS = src.ptr<uchar>(range.start);
        uchar* yD = dst.ptr<uchar>(range.start);

        for (int i = 0; i < len; ++i, yD++, yS += 3)
        {
            *yD = yS[0] | yS[1] | yS[2];
            //*yD = std::max(yS[0], std::max(yS[1], yS[2]));
        }
    }
};

void cvtBgrToGray_OR_Miki(const Mat3b& src, Mat1b& dst)
{
    dst.create(src.rows, src.cols);
    parallel_for_(Range(0, src.rows), ParallelBGRtoGrayOR(src, dst), -1);
}


// credits to @akarsakov
void cvtBgrToGray_OR_akarsakov(const Mat3b& src, Mat1b& dst)
{
    int rows = src.rows, cols = src.cols;
    dst.create(src.size());
    if (src.isContinuous() && dst.isContinuous())
    {
        cols = rows * cols;
        rows = 1;
    }

    for (int row = 0; row < rows; row++)
    {
        const uchar* src_ptr = src.ptr<uchar>(row);
        uchar* dst_ptr = dst.ptr<uchar>(row);

        for (int col = 0; col < cols; col++)
        {
            dst_ptr[col] = src_ptr[0] | src_ptr[1] | src_ptr[2];
            //dst_ptr[col] = std::max(src_ptr[0], std::max(src_ptr[1], src_ptr[2]));
            src_ptr += 3;
        }
    }
}

// credits to @Humam_Helfawi
void cvtBgrToGray_OR_Humam_Helfawi(const Mat3b& src, Mat1b& dst)
{
    cv::Mat channels[3];
    cv::split(src, channels);
    dst = channels[0] | channels[1] | channels[2];
}



int main()
{
    vector<Size> sizes{ Size(10, 10), Size(100, 100), Size(1000, 1000), Size(1280, 720), Size(1920, 1080), Size(4096, 3112), Size(10000, 10000) };

    cout << "Size: \t\takarsakov \tHumam Helfawi \tMiki \tOpenCV (not same operation)" << endl;

    for (int is = 0; is < sizes.size(); ++is)
    {
        Size sz = sizes[is];

        cout << sz << "\t";

        Mat3b img(sz);
        randu(img, Scalar(0, 0, 0), Scalar(255, 255, 255));

        Mat1b gray_akarsakov;
        Mat1b gray_Miki;
        Mat1b gray_Humam;
        Mat1b grayOpenCV;


        double tic = double(getTickCount());

        cvtBgrToGray_OR_akarsakov(img, gray_akarsakov);

        double toc = (double(getTickCount()) - tic) * 1000. / getTickFrequency();
        cout << toc << " \t";



        tic = double(getTickCount());

        cvtBgrToGray_OR_Humam_Helfawi(img, gray_Humam);

        toc = (double(getTickCount()) - tic) * 1000. / getTickFrequency();
        cout << toc << " \t";



        tic = double(getTickCount());

        cvtBgrToGray_OR_Miki(img, gray_Miki);

        toc = (double(getTickCount()) - tic) * 1000. / getTickFrequency();
        cout << toc << " \t";


        tic = double(getTickCount());

        cvtColor(img, grayOpenCV, COLOR_BGR2GRAY);

        toc = (double(getTickCount()) - tic) * 1000. / getTickFrequency();
        cout << toc << endl;

    }


    getchar();


    return 0;
}

Answer 2

OpenCV不包含任何合适的内置函数来以这种方式处理单独的通道.如果您想获得最佳性能,您可以自己实施此过程.我建议你这样的事情:

void calcOrChannels(const cv::Mat& src, cv::Mat& dst)
{
  CV_Assert(src.type() == CV_8UC3);
  int rows = src.rows, cols = src.cols;

  dst.create(src.size(), CV_8UC1);

  if (src.isContinuous() && dst.isContinuous())
  {
    cols = rows * cols;
    rows = 1;
  }

  for (int row = 0; row < rows; row++)
  {
    const uchar* src_ptr = src.ptr<uchar>(row);
    uchar* dst_ptr = dst.ptr<uchar>(row);

    for (int col = 0; col < cols; col++)
    {
      dst_ptr[col] = src_ptr[0] | src_ptr[1] | src_ptr[2]; // std::max(src_ptr[0], std::max(src_ptr[1], src_ptr[2]))
      src_ptr += 3;
    }
  }
}

请注意,您需要在硬件上测试此功能的性能,因为它通过使用在OpenCV中实现(或稍后实现)的SIMD指令和并行性而失去了好处.但是这个过程使用较少的额外内存和算术运算.我想它在大多数系统(尤其是嵌入式系统)上运行得更快.它还取决于矩阵的大小.

我系统上的计时(Core i7-4790):

| Matrix size | OpenCV (ms) | My (ms) |
|:-----------:|------------:|---------|
| 1280*720    | 4           | 1       |
| 1920*1080   | 8           | 2       |
| 4096*3112   | 41          | 17      |