Displaying a transferred HBITMAP in a picture control

Question

I have a camera which has a library developed in C# and a client application written in C++ 6. I have created a C# COM wrapper to link the two systems together and it is working quite well.

In the C# COM wrapper I have a System.Drawing.Bitmap object that contains the current frame from the camera.

In the C# COM wrapper I have a function public void GetFrameHandle(ref IntPtr hBitmap, [MarshalAs(UnmanagedType.SysInt)] ref int width, [MarshalAs(UnmanagedType.SysInt)] ref int height) which basically gets the HBITMAP from the frame bitmap into C++

This seems to work somewhat, and I can see the image in C++ but it is all garbled due to the pixelformat not being correct.

How can I determine the pixelformat from the HBITMAP in C++ and then display the correct image in the picture control?

I have performed a lot of investigation and it seems as if I need to create a new BITMAP from the transferred HBITMAP and then create a new HBITMAP from that which will be the correct pixel format and then use that to populate the picture control.

I'm not very sure how to begin this process

C# COM server:

    /// <summary>
    /// Called when an image has been grabbed and is ready to process
    /// </summary>
    /// <param name="sender"></param>
    /// <param name="e"></param>
    public void StreamGrabber_ImageGrabbed(object sender, ImageGrabbedEventArgs e)
    {

        // process the image
        try
        {
            // Acquire the image from the camera. Only show the latest image. The camera may acquire images faster than the images can be displayed.

            // Get the grab result.
            IGrabResult grabResult = e.GrabResult;

            // Check if the image can be displayed.
            if (grabResult.GrabSucceeded)
            {
                if (grabResult.IsValid)
                {
                    // create a new bitmap object for holding the image data from the camera
                    // the bits and things need to be able to be set according to the c++ program's requirements.
                    System.Drawing.Bitmap bitmap = new System.Drawing.Bitmap(grabResult.Width, grabResult.Height, System.Drawing.Imaging.PixelFormat.Format32bppRgb);
                    // Lock the bits of the bitmap.
                    System.Drawing.Imaging.BitmapData bmpData = bitmap.LockBits(new System.Drawing.Rectangle(0, 0, bitmap.Width, bitmap.Height), System.Drawing.Imaging.ImageLockMode.ReadWrite, bitmap.PixelFormat);
                    // Place the pointer to the buffer of the bitmap.
                    converter.OutputPixelFormat = PixelType.BGR8packed;
                    IntPtr ptrBmp = bmpData.Scan0;
                    converter.Convert(ptrBmp, bmpData.Stride * bitmap.Height, grabResult); //Exception handling TODO
                    bitmap.UnlockBits(bmpData);

                    // Assign a temporary variable to dispose the bitmap after assigning the new bitmap to the display control.
                    System.Drawing.Bitmap bitmapOld = this.currentFrame;
                    // Provide the display control with the new bitmap. This action automatically updates the display.
                    // this may require some mutex to ensure that only entire frames are retrieved
                    this.currentFrame = bitmap;

                    // if the client window is set, output bitmap to it.
                    if (m_clientWindow != null)
                        m_clientWindow.DrawImage(currentFrame, new System.Drawing.Point(0, 0));


                    if (bitmapOld != null)
                    {
                        // Dispose the bitmap.
                        bitmapOld.Dispose();
                    }

                    // notify that a frame is ready to obtain
                    BroadcastFrameEvent();
                }
            }
            else
            {
                BroadcastErrorEvent("StreamGrabber_ImageGrabbed", String.Format("Error: {0} {1}", grabResult.ErrorCode, grabResult.ErrorDescription));
            }
        }
        catch (Exception exception)
        {
            BroadcastErrorEvent("StreamGrabber_ImageGrabbed", exception.ToString());
        }
        finally
        {
            // Dispose the grab result if needed for returning it to the grab loop.
            e.DisposeGrabResultIfClone();
        }


    }


   public void GetFrameHandle(ref IntPtr hBitmap, [MarshalAs(UnmanagedType.SysInt)] ref int width, [MarshalAs(UnmanagedType.SysInt)] ref int height)
    {
        if (this.currentFrame != null)
        {
            // System.Drawing.Imaging.BitmapData bmpData = null;
            try
            {

                hBitmap = this.currentFrame.GetHbitmap();

                width = currentFrame.Width;
                height = currentFrame.Height;

            }
            catch (Exception ex)
            {
                BroadcastErrorEvent("GetFrame", ex.ToString());
            }
        }
    }


    public void SaveFrame(string filename)
    {
        try
        {
            if (m_debugMode == 1)
                MessageBox.Show("Filename = " + filename, "GigE COM Wrapper Debug");

            if (this.currentFrame != null)
                this.currentFrame.Save(filename, System.Drawing.Imaging.ImageFormat.Bmp);
        }
        catch (Exception ex)
        {
            BroadcastErrorEvent("SaveFrame", ex.ToString());
        }
    }

C++ client:

    // When a frame is ready to process
    HRESULT CameraEventHandler::OnFrameReady()
    {
        HRESULT hr = S_OK;

        //  if (m_debug == 1)
        //      MessageBox(NULL, "Frame is ready", "COM event received", MB_OK);

        // grab the frame from the COM wrapper and display it


        long pOutHb;

        if (pCamera != NULL)
        {
            BSTR bsFilename = SysAllocString(L"frame.bmp");

            hr = pCamera->SaveFrame(bsFilename);
            if (!SUCCEEDED(hr))
            {
                MessageBox(NULL, "COM Error", "Fail", MB_OK);
                return hr;
            }

            hr = pCamera->GetFrameHandle(&pOutHb, &width, &height);

            if (SUCCEEDED(hr))
            {

                BITMAP bm;
                HBITMAP hbFrameFromCOM;

                hbFrameFromCOM = (HBITMAP)pOutHb;

                // get the bitmap from the HBITMAP
                GetObject(hbFrameFromCOM, sizeof(BITMAP), &bm);

                LONG size = bm.bmWidthBytes * bm.bmHeight;

                        //create the bitmap?
                        // copy data across?
                        // create a new HBITMAP (hb)

                if (pDialog != NULL)
                {
                    // post the message
                    // this signals the dialog to update the picture control with the HBITMAP

                    pDialog->SendMessage(WM_REFRESH_BITMAP);
                }
            }
            else
                if (m_debug == 1)
                    MessageBox(NULL, "Get bitmap handle failed", "Fail", MB_OK);

        }

        return hr;
    }

Unsure how to proceed with this.

Interestingly, the frame.bmp that I'm saving from the C# code is also garbled. I think the two issues are related but I can't join the dots here.

Thanks for any help with it.

Answer 1

Thanks for the help I was able to get it working.

The code above was pretty much correct, except the pixelFormats needed to match in the C# COM wrapper between the camera and the bitmap that is used as the internal frame buffer.

The grayscale image output after the frame became stable was caused because I was setting the camera mode to grayscale in the c++ client. I changed it to YUV and it was all good.

There are a lot of places where modes can be set!

I didn't need to worry about changing anything in the C++ client. All that is required is to throw the HBITMAP sent by the COM wrapper at the dialog's picture control to display it.

Cheers.