How to access graphics from .NET in Mathematica?

Question

I would like to use Wolfram.NETLink.MathKernel.Graphics to retrieve an image generated from a Mathematica command. Which Mathematica command do I use to do this?

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using Wolfram.NETLink;
using System.IO;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            /*
                MathKernel kernel = new MathKernel();
                kernel.Compute("ExportString[Graphics[Rectangle[]],{\"Base64\",\"EMF\"}]");
                byte[] decodedBytes = Convert.FromBase64String(kernel.Result.ToString());
                File.WriteAllBytes("C:\\temp\\output.emf", decodedBytes);
            */

            MathKernel k = new MathKernel();
            k.CaptureGraphics = true;
            k.GraphicsFormat = "GIF";
            k.Compute("Show[Graphics[Rectangle[]]]");
            k.Graphics[0].Save("C:\\temp\\file.gif", System.Drawing.Imaging.ImageFormat.Gif);
        }
    }
}

Answer 1

I'm presuming that you already have a command which generates a graphics and you're trying to retrieve it through the MathKernel. If so, try the following:
1. Set the CaptureGraphics Property on your MathKernel to true.
2. Run MathKernel.Compute(command)
3. If your command successfully returned a graphics (you could check by Mathematica notebook), you should be able to retrieve it inside the MathKernel.Result.

---

Edit: My apologies, MathKernel.Result would tell you whether it succeeded or not (with $Failed signifying a failure). If it succeeded, you can retrieve it via .Graphics.
I'd also like to point out for anyone who may be dealing with this, that I've had to use the function UseFrontEnd quite frequently so that the graphics renders correctly.

Answer 2

To transfer an EMF graphic you can use this:

kernel.Compute("ExportString[Graphics[Rectangle[]],{\"Base64\",\"EMF\"}]");
byte[] decodedBytes = Convert.FromBase64String(kernel.Result.ToString());
File.WriteAllBytes("C:\\Temp\\output.emf", decodedBytes);

Ref: https://stackoverflow.com/questions/7755810/converting-graphics-with-exportstring

also: https://stackoverflow.com/questions/7542828/netlink-graphics-producing-png-instead-of-emf

GIF or JPEG graphics can be transferred via the MathKernel.Graphics property.

MathKernel k = new MathKernel();
k.CaptureGraphics = true;
k.GraphicsFormat = "GIF";
k.Compute("Show[Graphics[Rectangle[]]]");
k.Graphics[0].Save("C:\\Temp\\file.gif", System.Drawing.Imaging.ImageFormat.Gif);

Note Graphics is an array. Multiple images can be transferred in one operation.

Ref http://reference.wolfram.com/legacy/v7/NETLink/ref/net/Wolfram.NETLink.MathKernel.Graphics.html