/// <summary>Remove the corners of a window by replacing the background of these corners by transparency.</summary>
        private static Image RemoveCorners(IntPtr handle, Image windowImage, Bitmap redBGImage, Rectangle windowRect)
        {
            if (ZAppHelper.IsWindows8())
            {
                // Windows 8 UI does not have round corners
                return(windowImage);
            }

            const int cornerSize = 5;

            if (windowRect.Width > cornerSize * 2 && windowRect.Height > cornerSize * 2)
            {
                DebugHelper.WriteLine("Clean transparent corners");

                if (redBGImage == null)
                {
                    using (Form form = new Form())
                    {
                        form.FormBorderStyle = FormBorderStyle.None;
                        form.ShowInTaskbar   = false;
                        form.BackColor       = Color.Red;

                        NativeMethods.ShowWindow(form.Handle, (int)WindowShowStyle.ShowNormalNoActivate);
                        NativeMethods.SetWindowPos(form.Handle, handle, windowRect.X, windowRect.Y, windowRect.Width, windowRect.Height, NativeMethods.SWP_NOACTIVATE);
                        Application.DoEvents();
                        redBGImage = Screenshot.CaptureRectangleNative(windowRect) as Bitmap;
                    }
                }

                return(HelpersLib.GraphicsHelper.Core.RemoveCorners(windowImage, redBGImage));
            }
            return(null);
        }
        /// <summary>
        /// Make a full-size thumbnail of the captured window on a new topmost form, and capture
        /// this new form with a black and then white background. Then compute the transparency by
        /// difference between the black and white versions.
        /// This method has these advantages:
        /// - the full form is captured even if it is obscured on the Windows desktop
        /// - there is no problem with unpredictable Z-order anymore (the background and
        ///   the window to capture are drawn on the same window)
        /// </summary>
        /// <param name="handle">handle of the window to capture</param>
        /// <param name="windowRect">the bounds of the window</param>
        /// <param name="redBGImage">the window captured with a red background</param>
        /// <param name="captureRedBGImage">whether to do the capture of the window with a red background</param>
        /// <returns>the captured window image</returns>
        private static Image CaptureWindowWithDWM(IntPtr handle, Rectangle windowRect, out Bitmap redBGImage, Color backColor)
        {
            Image windowImage = null;

            redBGImage = null;

            if (backColor != Color.White)
            {
                backColor = Color.FromArgb(255, backColor.R, backColor.G, backColor.B);
            }

            using (Form form = new Form())
            {
                form.StartPosition   = FormStartPosition.Manual;
                form.FormBorderStyle = FormBorderStyle.None;
                form.ShowInTaskbar   = false;
                form.BackColor       = backColor;
                form.TopMost         = true;
                form.Bounds          = CaptureHelpers.GetWindowRectangle(handle, false);

                IntPtr thumb;
                NativeMethods.DwmRegisterThumbnail(form.Handle, handle, out thumb);

                SIZE size;
                NativeMethods.DwmQueryThumbnailSourceSize(thumb, out size);

#if DEBUG
                DebugHelper.WriteLine("Rectangle Size: " + windowRect.ToString());
                DebugHelper.WriteLine("Window    Size: " + size.ToString());
#endif

                if (size.Width <= 0 || size.Height <= 0)
                {
                    return(null);
                }

                DWM_THUMBNAIL_PROPERTIES props = new DWM_THUMBNAIL_PROPERTIES();
                props.dwFlags       = NativeMethods.DWM_TNP_VISIBLE | NativeMethods.DWM_TNP_RECTDESTINATION | NativeMethods.DWM_TNP_OPACITY;
                props.fVisible      = true;
                props.opacity       = (byte)255;
                props.rcDestination = new RECT(0, 0, size.Width, size.Height);

                NativeMethods.DwmUpdateThumbnailProperties(thumb, ref props);

                form.Show();
                System.Threading.Thread.Sleep(250);

                if (form.BackColor != Color.White)
                {
                    // no need for transparency; user has requested custom background color
                    NativeMethods.ActivateWindowRepeat(form.Handle, 250);
                    windowImage = Screenshot.CaptureRectangleNative(windowRect) as Bitmap;
                }
                else if (form.BackColor == Color.White)
                {
                    // transparent capture
                    NativeMethods.ActivateWindowRepeat(handle, 250);
                    Bitmap whiteBGImage = Screenshot.CaptureRectangleNative(windowRect) as Bitmap;

                    form.BackColor = Color.Black;
                    form.Refresh();
                    NativeMethods.ActivateWindowRepeat(handle, 250);
                    Bitmap blackBGImage = Screenshot.CaptureRectangleNative(windowRect) as Bitmap;

                    // Capture rounded corners with except for Windows 8
                    if (ZAppHelper.IsWindows8())
                    {
                        form.BackColor = Color.Red;
                        form.Refresh();
                        NativeMethods.ActivateWindowRepeat(handle, 250);
                        redBGImage = Screenshot.CaptureRectangleNative(windowRect) as Bitmap;
                    }

                    form.BackColor = Color.White;
                    form.Refresh();
                    NativeMethods.ActivateWindowRepeat(handle, 250);
                    Bitmap whiteBGImage2 = Screenshot.CaptureRectangleNative(windowRect) as Bitmap;

                    // Don't do transparency calculation if an animated picture is detected
                    if (whiteBGImage.AreBitmapsEqual(whiteBGImage2))
                    {
                        windowImage = HelpersLib.GraphicsHelper.Core.ComputeOriginal(whiteBGImage, blackBGImage);
                    }
                    else
                    {
                        DebugHelper.WriteLine("Detected animated image => cannot compute transparency");
                        form.Close();
                        Application.DoEvents();
                        Image result = new Bitmap(whiteBGImage.Width, whiteBGImage.Height, PixelFormat.Format32bppArgb);
                        using (Graphics g = Graphics.FromImage(result))
                        {
                            // Redraw the image on a black background to avoid transparent pixels artifacts
                            g.Clear(Color.Black);
                            g.DrawImage(whiteBGImage, 0, 0);
                        }
                        windowImage = result;
                    }

                    blackBGImage.Dispose();
                    whiteBGImage.Dispose();
                    whiteBGImage2.Dispose();
                }

                NativeMethods.DwmUnregisterThumbnail(thumb);
            }

            return(windowImage);
        }