I'm trying to access the pixel colors from a image file but can't seem to get it to work properly, my program is only accessing the pixel colors from my active window. I've been stuck on this for a few days and would really appreciate any help. I'm guessing i haven't set a proper handle to a device context to the image but i don't know how to do this

    HWND hDesktopWnd; HDC hDesktopDC; HDC hCaptureDC; 
    HBITMAP hCaptureBitmap; 
    BITMAPINFO bmi = {0};
    RGBQUAD *pPixels;
    LPTSTR szFileName; 
    BITMAP  bm;  int nScreenWidth, nScreenHeight; 
    szFileName = "test.bmp";

                nScreenWidth =  GetSystemMetrics(SM_CXSCREEN);
                nScreenHeight = GetSystemMetrics(SM_CYSCREEN);
                hDesktopWnd = GetDesktopWindow();
                hDesktopDC = GetDC(hwnd);
                hCaptureDC = CreateCompatibleDC(hDesktopDC);
                hCaptureBitmap = (HBITMAP)LoadImage( NULL, szFileName, IMAGE_BITMAP, 0, 0, LR_CREATEDIBSECTION | LR_DEFAULTSIZE | LR_LOADFROMFILE );
                SelectObject(hCaptureDC, hCaptureBitmap); 
                BitBlt(hCaptureDC, 0, 0, nScreenWidth, nScreenHeight, hDesktopDC, 0,0, SRCCOPY|CAPTUREBLT); 

                bmi.bmiHeader.biSize = sizeof(bmi.bmiHeader);
                bmi.bmiHeader.biWidth = nScreenWidth;
                bmi.bmiHeader.biHeight = nScreenHeight;
                bmi.bmiHeader.biPlanes = 1;
                bmi.bmiHeader.biBitCount = 32;
                bmi.bmiHeader.biCompression = BI_RGB;

                pPixels = new RGBQUAD[nScreenWidth * nScreenHeight];

                ::GetDIBits(hCaptureDC,
                            hCaptureBitmap,
                            0,  
                            nScreenHeight,  
                            pPixels, 
                            &bmi,  
                            DIB_RGB_COLORS); 

                for(int i= 0;i< nScreenHeight; i++){
                for(int j= 0;j< nScreenWidth; j++){
                    col.red_palette[i][j]   = pPixels[(nScreenWidth * (nScreenHeight-(i+1))) + j].rgbRed;   
                    col.green_palette[i][j] = pPixels[(nScreenWidth * (nScreenHeight-(i+1))) + j].rgbGreen; 
                    col.blue_palette[i][j]  = pPixels[(nScreenWidth * (nScreenHeight-(i+1))) + j].rgbBlue;  
                }
                }

                delete [] pPixels;
                ReleaseDC(hDesktopWnd, hDesktopDC);
                DeleteDC(hCaptureDC);
                DeleteObject(hCaptureBitmap);