Saving DrawingVisual to an image file with a given DPI

Question

I have got a WPF application, and I would like to save a Canvas to a file with a correct DPI value. The Canvas size is the real physical size, eg. 20x10 cm, at 300 DPI, so it\'s

Answer 1

The following method saves a UIElement to a JPEG file with the specified DPI value:

public static void SaveElement(UIElement element, double dpi, string path)
{
    var visual = new DrawingVisual();
    var width = element.RenderSize.Width;
    var height = element.RenderSize.Height;

    using (var context = visual.RenderOpen())
    {
        context.DrawRectangle(new VisualBrush(element), null,
            new Rect(0, 0, width, height));
    }

    var bitmap = new RenderTargetBitmap(
        (int)(width * dpi / 96), (int)(height * dpi / 96),
        dpi, dpi, PixelFormats.Default);
    bitmap.Render(visual);

    var encocer = new JpegBitmapEncoder();
    encocer.Frames.Add(BitmapFrame.Create(bitmap));

    using (var stream = File.OpenWrite(path))
    {
        encocer.Save(stream);
    }
}

Alternatively, apply the DPI scaling to the DrawingVisual:

public static void SaveElement(UIElement element, double dpi, string path)
{
    var visual = new DrawingVisual();
    var width = element.RenderSize.Width;
    var height = element.RenderSize.Height;

    using (var context = visual.RenderOpen())
    {
        context.DrawRectangle(new VisualBrush(element), null,
            new Rect(0, 0, width / dpi * 96, height / dpi * 96));
    }

    var bitmap = new RenderTargetBitmap(
        (int)width, (int)height, dpi, dpi, PixelFormats.Default);
    bitmap.Render(visual);

    var encocer = new JpegBitmapEncoder();
    encocer.Frames.Add(BitmapFrame.Create(bitmap));

    using (var stream = File.OpenWrite(path))
    {
        encocer.Save(stream);
    }
}