OpenCV: "draw" image on another image-CodePudding

I have 2 images with transparency. Images have the same format and size. How can I copy pixels from second image to the first one by using C OpenCV? The idea is to draw 2nd image on the 1st image.

Thanks

CodePudding user response：

code from the link in comment above (modified for my case) L. Scott Johnson thanks you again!

void alphaBlend(Mat& foreground, Mat& background, Mat& alpha, Mat& outImage)
{
    // Find number of pixels.
    int numberOfPixels = foreground.rows * foreground.cols * foreground.channels();

    // Get floating point pointers to the data matrices

    float* fptr = reinterpret_cast<float*>(foreground.data);
    float* bptr = reinterpret_cast<float*>(background.data);
    float* aptr = reinterpret_cast<float*>(alpha.data);
    float* outImagePtr = reinterpret_cast<float*>(outImage.data);


    // Loop over all pixesl ONCE

    for (
        int i = 0;
        i < numberOfPixels;
        i  , outImagePtr  , fptr  /*, aptr  */,  bptr  
        )
    {
        if (i!= 0 && (i % 3) == 0)
            aptr  ;

        *outImagePtr = (*fptr) * (*aptr)   (*bptr) * (1 - *aptr);
    }
}


void Mix()
{
    Mat layer = imread("images\\leyer.png", IMREAD_UNCHANGED);
    Mat image = imread("images\\bg.jpg");
    
    std::vector<cv::Mat> bgra_planes;
    cv::split(layer, bgra_planes);
    
    Mat alpha = bgra_planes[3];

    bgra_planes.pop_back();
    cv::merge(bgra_planes, layer);

    alpha.convertTo(alpha, CV_32FC3, 1.0 / 255);
    layer.convertTo(layer, CV_32FC3);
    image.convertTo(image, CV_32FC3);


    Mat result(layer.size(), CV_32FC3);

    alphaBlend(layer, image, alpha, result);

    result.convertTo(result, CV_8UC3);

    // previous tries
    //cv::copyTo(layer, image, );
    //cv::addWeighted(image, 1, layer, 1, 0.5, result);

    String windowName = "alpha blending"; 
    namedWindow(windowName, WINDOW_NORMAL); 
    imshow(windowName, result); 
    waitKey(0); 
    destroyWindow(windowName); 
}

CodePudding user response：

Here's what you can try:

load your first image

cv::Mat img = cv::imread("img.jpeg");

find your smaller image - here I'm just resizing the same image

cv::Mat img_resize;
cv::resize(img, img_resize, cv::Size(), 0.3, 0.3);

choose the xy origin location

const cv::Point origin(100, 100);

create a Region of Interest

cv::Rect roi(origin, img_resize.size());

copy the matrix data in

img_resize.copyTo(img(roi));