CODEWITHSUNDEEP
c++opencv
NoxAtra
NoxAtra

Reputation: 81

OpenCV image zoomed in

I'm using this function to make a screenshot of a window. It works fine but at games like Minecraft it's zoomed in.

Normal Normal Screenshot Screenshot

cv::Mat getMat(HWND hWND) {
    HDC deviceContext = GetDC(hWND);
    HDC memoryDeviceContext = CreateCompatibleDC(deviceContext);

    RECT windowRect;
    GetClientRect(hWND, &windowRect);

    int height = windowRect.bottom;
    int width = windowRect.right;

    HBITMAP bitmap = CreateCompatibleBitmap(deviceContext, width, height);

    SelectObject(memoryDeviceContext, bitmap);

    //copy data into bitmap
    BitBlt(memoryDeviceContext, 0, 0, width, height, deviceContext, 0, 0, SRCCOPY);

    //specify format by using bitmapinfoheader!
    BITMAPINFOHEADER bi;
    bi.biSize = sizeof(BITMAPINFOHEADER);
    bi.biWidth = width;
    bi.biHeight = -height;
    bi.biPlanes = 1;
    bi.biBitCount = 32;
    bi.biCompression = BI_RGB;
    bi.biSizeImage = 0; //because no compression
    bi.biXPelsPerMeter = 1; 
    bi.biYPelsPerMeter = 2; 
    bi.biClrUsed = 3; 
    bi.biClrImportant = 4; 

    cv::Mat mat = cv::Mat(height, width, CV_8UC4); // 8 bit unsigned ints 4 Channels -> RGBA

    //transform data and store into mat.data
    GetDIBits(memoryDeviceContext, bitmap, 0, height, mat.data, (BITMAPINFO*)&bi, DIB_RGB_COLORS);

    //clean up!
    DeleteObject(bitmap);
    DeleteDC(memoryDeviceContext); //delete not release!
    ReleaseDC(hWND, deviceContext);

    return mat;
}

Upvotes: 2

Views: 103

Answers (1)

Arritmic
Arritmic

Reputation: 509

According to the documentation, windowRect.bottom is not the height. Or windowRect.right is not the width. https://learn.microsoft.com/en-us/windows/win32/api/windef/ns-windef-rect

So, you should do something like this:

int height = windowRect.bottom - windowRect.top;
int width = windowRect.right - windowRect.left;

EDIT1: I have found an issue similar to yours. Maybe it could help you as well. ClientRect mysteriously smaller than WindowRect?

Cheers.

Upvotes: 2

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