opencv4 学习 04 掩码操作和图像混合

1.掩码操作

对图片每个像素做如下变换：

p[i,j] = 5*p[i,j] - p[i,j-1] - p[i,j+1] - p[i-1,j] - p[i+1,j]

p[i,j] 表示当前像素。

首先手动实现一个该函数，代码如 sharpen 函数，然后和opencv内置的filter2D函数做比较。

#include <opencv2/imgcodecs.hpp>
#include <opencv2/highgui.hpp>
#include <opencv2/imgproc.hpp>
#include <iostream>
using namespace std;
using namespace cv;

void sharpen(const Mat& myImage, Mat& Result)
{
    CV_Assert(myImage.depth()==CV_8U);

    const int nchannels = myImage.channels();
    Result.create(myImage.size(),myImage.type());

    for(int j=1; j<myImage.rows-1;++j)
    {
        const uchar* previous = myImage.ptr<uchar>(j-1);
        const uchar* current = myImage.ptr<uchar>(j);
        const uchar* next = myImage.ptr<uchar>(j+1);
        uchar* output = Result.ptr<uchar>(j);
        for(int i=nchannels;i<(myImage.cols-1)*nchannels;++i)
        {
            *output++ = saturate_cast<uchar>(5*current[i] - current[i-nchannels] - current[i+nchannels] - previous[i] - next[i]);
        }
    }

    Result.row(0).setTo(Scalar(0));
    Result.row(Result.rows-1).setTo(Scalar(0));
    Result.col(0).setTo(Scalar(0));
    Result.col(Result.cols-1).setTo(Scalar(0));
}

int main(int argc, char* argv[])
{
    Mat src, dst0, dst1;
    string filename = "lena.jpg";
    src = imread(filename, IMREAD_COLOR);

    namedWindow("Input", WINDOW_AUTOSIZE);
    namedWindow("Output", WINDOW_AUTOSIZE);

    imshow("Input", src);

    double t = (double)getTickCount();
    sharpen(src,dst0);
    t = ((double)getTickCount() - t)/getTickFrequency();
    cout << "Hand written function time passed in seconds: " << t << endl;
    imshow("Output", dst0);
    waitKey();

    // Built-in function
    Mat kernel = (Mat_<char>(3,3) << 0, -1, 0,
                                    -1, 5, -1,
                                     0, -1, 0);
    t = (double)getTickCount();
    filter2D(src, dst1, src.depth(), kernel);
    t = ((double)getTickCount()-t)/getTickFrequency();
    cout << "Built-in filter2D time passed in seconds: " << t << endl;
    imshow("Output", dst1);
    waitKey();

    return 0;
}

耗时如下：

Hand written function time passed in seconds: 0.00977115

Built-in filter2D time passed in seconds: 0.00188034

2.图像混合

addWeighted() 函数的使用

int main(int argc, char* argv[])
{
    double alpha = 0.5;
    double beta = 1 - alpha;
    Mat src1, src2, dst;

    src1 = imread("LinuxLogo.jpg");
    src2 = imread("WindowsLogo.jpg");
    // dst = src1*alpha + src2*beta + gamma
    addWeighted(src1, alpha, src2. beta, 0.0, dst);
    imshow("Linear Blend", dst);
    waitKey(0);

    return 0;
}

 

参考：

https://docs.opencv.org/3.4/d7/d37/tutorial_mat_mask_operations.html

https://docs.opencv.org/3.4/d5/dc4/tutorial_adding_images.html