c++ opencv displaying image on a window

Question

I want to load an image using OpenCV and then display it on a window.

I know how to load an image using opencv and how to create a window using win32 but how do I go about putting the image / mat from Opencv on the window afterwards?

This is how I load the image from opencv:

#include <opencv2/core/core.hpp>
#include <opencv2/imgcodecs.hpp>
#include <opencv2/highgui/highgui.hpp>

#include <iostream>
#include <string>
using namespace cv;

using namespace std;

int main(int argc, char** argv)
{

    string imageName("C:/image.jpg"); // by default
    if (argc > 1)
    {
        imageName = argv[1];
    }

    Mat image;



    image = imread(imageName.c_str(), IMREAD_COLOR); 


    if (image.empty())     
    {
        cout << "Could not open or find the image" << std::endl;
        return -1;
    }


    namedWindow("Display window", WINDOW_AUTOSIZE);

    imshow("Display window", image); 


    waitKey(0);
    return 0;
}

EDIT: The reason I want to do this is actually not to create a window during runtime and then display the image on it, but rather I want to find a window using win32's FindWindow function and then draw an image on that :D

Answer 1

I'm using this pretty often with my MFC projects. If you only have hwnd, not CWnd, then you may have to change a bit.

This works both with 8-bit RGB color and 1-channel monochrome image.

    void DrawImage( CWnd *wnd, int width, int height, int bpp, const unsigned char *buffer)
{
    RECT rect;
    wnd->GetWindowRect(&rect);
    CDC *dc = wnd->GetDC();

    if( bpp == 3) // BGR
    {
        BITMAPINFO bmpinfo;

        memset(&bmpinfo, 0, sizeof(bmpinfo));
        bmpinfo.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
        bmpinfo.bmiHeader.biBitCount = 24;
        bmpinfo.bmiHeader.biClrImportant = 0;
        bmpinfo.bmiHeader.biClrUsed = 0;
        bmpinfo.bmiHeader.biCompression = BI_RGB;
        bmpinfo.bmiHeader.biWidth = width;
        bmpinfo.bmiHeader.biHeight = -height;
        bmpinfo.bmiHeader.biPlanes = 1;
        bmpinfo.bmiHeader.biSizeImage = 0;
        bmpinfo.bmiHeader.biXPelsPerMeter = 100;
        bmpinfo.bmiHeader.biYPelsPerMeter = 100;

        ::SetStretchBltMode( dc->GetSafeHdc(), COLORONCOLOR);
        ::StretchDIBits(    dc->GetSafeHdc(),
                        0,
                        0,
                        rect.right - rect.left, 
                        rect.bottom - rect.top,
                        0,
                        0,
                        width,
                        height,
                        buffer,
                        &bmpinfo,
                        DIB_RGB_COLORS,
                        SRCCOPY);
    }
    else if ( bpp == 1) // monochrome.
    {
        char bitmapInfoBuf[sizeof(BITMAPINFO) + 4 * 256];
        BITMAPINFO* pBmpInfo = (BITMAPINFO*)bitmapInfoBuf;

        memset(pBmpInfo, 0, sizeof(BITMAPINFO) + 4 * 256);
        pBmpInfo->bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
        pBmpInfo->bmiHeader.biWidth = width;
        pBmpInfo->bmiHeader.biHeight = -height;
        pBmpInfo->bmiHeader.biCompression = BI_RGB;
        pBmpInfo->bmiHeader.biPlanes = 1;
        pBmpInfo->bmiHeader.biBitCount = 8;

        for(int i = 0; i < 256; i++)
        {
            pBmpInfo->bmiColors[i].rgbBlue=i;
            pBmpInfo->bmiColors[i].rgbGreen=i;
            pBmpInfo->bmiColors[i].rgbRed=i;
            pBmpInfo->bmiColors[i].rgbReserved=255;
        }

        ::SetStretchBltMode( dc->GetSafeHdc(), COLORONCOLOR);
        ::StretchDIBits( dc->GetSafeHdc(),
                        0, 
                        0, 
                        rect.right - rect.left, 
                        rect.bottom - rect.top, 
                        0, 
                        0, 
                        width, 
                        height, 
                        buffer, 
                        pBmpInfo, 
                        DIB_RGB_COLORS, 
                        SRCCOPY);
    }

    wnd->ReleaseDC(dc);
}

void DrawCVImage(cv::Mat image, CWnd *picture)
{
    if (image.cols % 4 == 0)
    {
        DrawImage(picture, 
            image.cols, 
            image.rows,
            image.channels() == 3 ? 3 : 1,
            image.data);
    }
    else
    {
        Mat image2(image.rows, image.cols + ( 4 - image.cols % 4), image.type());
        image2 = 0;
        image.copyTo(image2(Rect(0, 0, image.cols, image.rows)));

        DrawImage(picture, 
            image2.cols, 
            image2.rows,
            image2.channels() == 3 ? 3 : 1,
            image2.data);
    }
}

Answer 2

Well...

Don't create a new window by calling "namedWindow()".

Then call imshow(nameOfExistingWindow, image).

Maybe it will work.