GraphicOverlay

Graphic Overlay

This example demonstrates how graphics can be drawn on the live video and displayed in IC Imaging Control's ic4.WinForms.Display.

Prerequisites

• The Imaging Source camera or video capture device
• IC4 GenTL Producer for the above mentioned device
• Visual Studio™ C#, .NET 6

Implementation

The program displays a red line on top of each image coming from the camera.

To do this, an ic4.QueueSink is created that raises an event for every new image.

The event handler calls QueueSink.PopOutputBuffer() to retrieve the image buffer.

The ic4dotnet.System.Drawing assembly provides the extension method ImageBuffer.CreateBitmapWrap() which creates a System.Drawing.Bitmap that shares the image buffer's memory.

To draw the overlay, a System.Drawing.Graphics object is created for the bitmap. Drawing operations on this object modify the contents of the image buffer.

Finally, the modified image buffer is passed to an ic4.WinForms.Display control for display.

Setup the QueueSink

In the startStream method the sink is created:

sink = new ic4.QueueSink(ic4.PixelFormat.BGRa8);

Graphics.FromImage() only supports RGB pixel formats. We therefore request a conversion to BGRa8 to make sure System.Drawing can draw into the image buffer. (BGR8 would be possible as well.)

Then register the FramesQueued event handler to this sink:

sink.FramesQueued += sink_FramesQueued;

The complete start method is:

void startStream()
{
    if (!grabber.IsStreaming)
    {
        // Create the sink for continuous image processing.
        // We want to use BGRa8 (RGB32) in the sink, which 
        // allows us to use System.Drawing.Graphics for drawing.                
        try
        {
            var sink = new ic4.QueueSink(ic4.PixelFormat.BGRa8);
            sink.FramesQueued += sink_FramesQueued;

            grabber.StreamSetup(sink );   
            
        }
        catch( IC4Exception iex)
        {
            MessageBox.Show($"Error starting stream:\n{iex.Message}", 
                "Graphic Overlay",
                MessageBoxButtons.OK, MessageBoxIcon.Error);
        }
    }
    updateControls();
}

Please note: The ic4.WinForms.Display display object ic4Display is not passed to StreamSetup, since the modified image buffers are passed manually in the QueueSink.FramesQueued event handler. If the data stream displayed automatically the camera images as well, the display could flicker between modified and unmodified image buffers.

Drawing on the live video

private void sink_FramesQueued(object sender, QueueSinkEventArgs e)
{
    using var buffer = e.Sink.PopOutputBuffer();

    // Create a System.Drawing.Bitmap which shares the memory
    // of the image buffer.                
    using var bitmap = buffer.CreateBitmapWrap();

    // Now draw a line.
    using var g = Graphics.FromImage(bitmap);
    g.DrawLine(new Pen(Color.Red, 3), 10, 10, 200, 200);

    // Now draw the image with the line in IC Imaging Display Control
    // This works fine, because buffer and bitmap share the same
    // memory. 
    ic4Display.DisplayBuffer(buffer);
}