I have 2 transparent images which I want them to be opened in one window in opencv. The code below opens two images but with out alpha channel because it's using (CV_8UC3) and those images which are transparent we should use (CV_8UC4) to show the transparency but when I change the code to (CV_8UC4) the program gives me an error.

I'll make (CV_8UC4) and error line bold;

the original code is (CV_8UC3)

microsoft visual studio error dialog shows this error : Unhandled exception at 0x00007FFA48633FB8 in openCV.exe: Microsoft C++ exception: cv::Exception at memory location 0x0000007563FDEA00. and the console application window shows this one : OpenCV Error: Assertion failed (channels() == CV_MAT_CN(dtype)) in cv::Mat::copyTo, file C:\build\master_winpack-build-win64-vc14\opencv\modules\core\src\copy.cpp, line 272

Is this code suitable for what I want to do?

This code opens multiple images but i've use it for two.

code is:

    void ShowManyImages(string title, int nArgs, ...) {
    int size;
    int i;
    int m, n;
    int x, y;

    // w - Maximum number of images in a row
    // h - Maximum number of images in a column
    int w, h;

    // scale - How much we have to resize the image
    float scale;
    int max;

    // If the number of arguments is lesser than 0 or greater than 12
    // return without displaying
    if (nArgs <= 0) {
        printf("Number of arguments too small....\n");
        return;
    }
    else if (nArgs > 14) {
        printf("Number of arguments too large, can only handle maximally 12 images at a time ...\n");
        return;
    }
    // Determine the size of the image,
    // and the number of rows/cols
    // from number of arguments
    else if (nArgs == 1) {
        w = h = 1;
        size = 300;
    }
    else if (nArgs == 2) {
        w = 2; h = 1;
        size = 1000;
    }
    else if (nArgs == 3 || nArgs == 4) {
        w = 2; h = 2;
        size = 300;
    }
    else if (nArgs == 5 || nArgs == 6) {
        w = 3; h = 2;
        size = 200;
    }
    else if (nArgs == 7 || nArgs == 8) {
        w = 4; h = 2;
        size = 200;
    }
    else {
        w = 4; h = 3;
        size = 150;
    }

    // Create a new 3 channel image

Mat DispImage = Mat::zeros(Size(100 + sizew, 60 + sizeh), CV_8UC4);

    // Used to get the arguments passed
    va_list args;
    va_start(args, nArgs);

    // Loop for nArgs number of arguments
    for (i = 0, m = 20, n = 20; i < nArgs; i++, m += (0)) {
        // Get the Pointer to the IplImage
        Mat img = va_arg(args, Mat);

        // Check whether it is NULL or not
        // If it is NULL, release the image, and return
        if (img.empty()) {
            printf("Invalid arguments");
            return;
        }

        // Find the width and height of the image
        x = img.cols;
        y = img.rows;

        // Find whether height or width is greater in order to resize the image
        max = (x > y) ? x : y;

        // Find the scaling factor to resize the image
        scale = (float)((float)max / size);

        // Used to Align the images
        if (i % w == 0 && m != 20) {
            m = 20;
            n += 20 + size;
        }

        // Set the image ROI to display the current image
        // Resize the input image and copy the it to the Single Big Image
        Rect ROI(m, n, (int)(x / scale), (int)(y / scale));
        Mat temp; resize(img, temp, Size(ROI.width, ROI.height));

temp.copyTo(DispImage(ROI));

    }

    // Create a new window, and show the Single Big Image
    namedWindow(title, 1);
    imshow(title, DispImage);
    waitKey();

    // End the number of arguments
    va_end(args);
}

int main(int argc, char** argv)
{
    Mat img1 = imread("c:\\1.png");
    Mat img2 = imread("c:\\2.png");
    ShowManyImages("Image", 2, img1, img2);

    return 0;
}