source: OniSplit/Imaging/SysReader.cs

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Drawing.Imaging;
using System.Runtime.InteropServices;

namespace Oni.Imaging
{
        internal static class SysReader
        {
                public static Surface Read(string filePath)
                {
                        using (Bitmap bmp = new Bitmap(filePath, false))
                        {
                                SurfaceFormat surfaceFormat;
                                PixelFormat pixelFormat;

                                if (bmp.RawFormat == ImageFormat.Jpeg || bmp.RawFormat == ImageFormat.Bmp)
                                {
                                        surfaceFormat = SurfaceFormat.BGRX;
                                        pixelFormat = PixelFormat.Format32bppRgb;
                                }
                                else
                                {
                                        surfaceFormat = SurfaceFormat.BGRA;
                                        pixelFormat = PixelFormat.Format32bppArgb;
                                }

                                var surface = new Surface(bmp.Width, bmp.Height, surfaceFormat);
                var rc = new Rectangle(0, 0, bmp.Width, bmp.Height);
                
                var data = bmp.LockBits(rc, ImageLockMode.ReadOnly, pixelFormat);
                                Marshal.Copy(data.Scan0, surface.Data, 0, surface.Data.Length);
                                bmp.UnlockBits(data);

                return surface;
                        }
                }
        }
}