RenderTargetBitmap is blurry

Question

Hi i'm creating an image in memory from a Canvas using a PngBitmapEncoder.

public void CaptureGraphic()
{
    Canvas canvas = new Canvas();
    canvas.SnapsToDevicePixels = true;
    canvas.Height = IMAGEHEIGHT;
    canvas.Width = IMAGEWIDTH;
    Draw(canvas);
    canvas.Arrange(new Rect(0, 0, IMAGEWIDTH, IMAGEHEIGHT));
    member.MemberImage = GetPngFromUIElement(canvas);
}

public static System.Drawing.Image GetPngFromUIElement(Canvas source)
{
    int width = (int)source.ActualWidth;
    int height = (int)source.ActualHeight;

    if (width == 0)
        width = (int)source.Width;
    if (height == 0)
        height = (int)source.Height;


    RenderTargetBitmap bitmap = new RenderTargetBitmap(width, height, 96d, 96d, PixelFormats.Pbgra32);
    bitmap.Render(source);

    PngBitmapEncoder enc = new PngBitmapEncoder();
    enc.Interlace = PngInterlaceOption.Off;
    enc.Frames.Add(BitmapFrame.Create(bitmap));

    System.IO.MemoryStream ms = new System.IO.MemoryStream();
    enc.Save(ms);

    System.Drawing.Image image = System.Drawing.Image.FromStream(ms);

    ms.Flush();
    ms.Dispose();

    return image;
}

Then i'm sending the image to the printer using the GDI+ DrawImage() method. However the printed result is blurry.

I've tried to match the original canvas size to the printed size to avoid any scaling, equally i've tried to make the original considerably bigger so the scaled image retains the quality however the final printed image is always blurred.

Can anyone offer any suggestions/alternatives. I have a considerable GDI+ print routine already setup and moving to wpf documents is not an option just yet.

Thanks

Answer 1

You're capturing the bitmap at 96 DPI. Instead of using 96 in the constructor of the RenderTargetBitmap, try to match the DPI of your printer output. Alternatively, you could do the math and calculate the difference in width/height and rescale the image on the report accordingly (the result is the image on the report will appear smaller).

Answer 2

I had the same blurry result and have come up with the following piece of code, which applies the same idea with the offset, but using the Offset property on the DrawingVisual (since I was using DrawDrawing, which doesn't have an overload with the offset argument):

public static Image ToBitmap(Image source)
{
    var dv = new DrawingVisual();
    // Blur workaround
    dv.Offset = new Vector(0.5, 0.5);
    using (var dc = dv.RenderOpen())
        dc.DrawDrawing(((DrawingImage)source.Source).Drawing);

    var bmp = new RenderTargetBitmap((int)source.Width, (int)source.Height, 96, 96, PixelFormats.Pbgra32);
    bmp.Render(dv);

    var bitMapImage = new Image();
    bitMapImage.Source = bmp;
    bitMapImage.Width = source.Width;
    bitMapImage.Height = source.Height;

    return bitMapImage;
}