GraphLibrary/DrawGraph/Export.cs

using System.IO;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;
using System.Windows.Media.Imaging;

namespace DrawGraph
{
    class Export
    {
        public static void ToPng(Canvas canvas, string path)
        {
            RenderTargetBitmap renderBitmap = new RenderTargetBitmap(
                (int)canvas.Width, (int)canvas.Height,
                96d, 96d, PixelFormats.Pbgra32);
            canvas.Measure(new Size((int)canvas.Width, (int)canvas.Height));
            canvas.Arrange(new Rect(new Size((int)canvas.Width, (int)canvas.Height)));

            renderBitmap.Render(canvas);

            //JpegBitmapEncoder encoder = new JpegBitmapEncoder();
            PngBitmapEncoder encoder = new PngBitmapEncoder();
            encoder.Frames.Add(BitmapFrame.Create(renderBitmap));

            using (FileStream fs = new FileStream(path, FileMode.Create))
            {
                encoder.Save(fs);
            }
        }

        public static void ToJpeg(Canvas canvas, string path)
        {
            RenderTargetBitmap renderBitmap = new RenderTargetBitmap(
                (int)canvas.Width, (int)canvas.Height,
                96d, 96d, PixelFormats.Pbgra32);
            canvas.Measure(new Size((int)canvas.Width, (int)canvas.Height));
            canvas.Arrange(new Rect(new Size((int)canvas.Width, (int)canvas.Height)));

            renderBitmap.Render(canvas);

            JpegBitmapEncoder encoder = new JpegBitmapEncoder();
            encoder.Frames.Add(BitmapFrame.Create(renderBitmap));

            using (FileStream fs = new FileStream(path, FileMode.Create))
            {
                encoder.Save(fs);
            }
        }

        public static void Print(Canvas canvas)
        {
            PrintDialog pd = new PrintDialog();
            if (pd.ShowDialog() == true)
            {
                pd.PrintVisual(canvas, "Printed with DrawGraph");
            }
        }
    }
}