Updated comments on sync context.

NTwain/Internals/TransferLogic.cs

@@ -1,6 +1,7 @@
 using NTwain.Data;
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.IO;
 using System.Linq;
 using System.Runtime.InteropServices;

NTwain/TwainSession.cs

@@ -564,6 +564,8 @@ namespace NTwain
             var syncer = SynchronizationContext;
             if (syncer == null)
             {
+                Debug.WriteLine(string.Format(CultureInfo.InvariantCulture, "Trying to raise event {0} on thread {1} without sync.", e.GetType().Name, Thread.CurrentThread.ManagedThreadId));
+
                 try
                 {
                     onEventFunc(e);
@@ -573,6 +575,8 @@ namespace NTwain
             }
             else
             {
+                Debug.WriteLine(string.Format(CultureInfo.InvariantCulture, "Trying to raise event {0} on thread {1} with sync.", e.GetType().Name, Thread.CurrentThread.ManagedThreadId));
+                // on some consumer desktop scanner with poor drivers this can frequently hang. there's nothing I can do here.
                 syncer.Send(o =>
                 {
                     try

README.md

@@ -76,7 +76,9 @@ example for handling DIB image in native transfer using the CommonWin32 lib.
 
 Because it hosts its own message thread, the events will likely be raised from another thread. 
 If you would like things marshalled to a UI thread then set the SynchronizationContext property
-to the one from the UI thread. 
+to the one from the UI thread. Note that on certain consumer-grade scanner drivers this may hang the 
+event, so if you find yourself in that position you'll have to find another way
+to synchronize data to UI threads.
 
 
 ```

Tests/Tester.Winform/TestForm.cs

@@ -61,42 +61,38 @@ namespace Tester.Winform
             _twain.SynchronizationContext = SynchronizationContext.Current;
             _twain.StateChanged += (s, e) =>
             {
-                Debug.WriteLine("State change on thread " + Thread.CurrentThread.ManagedThreadId);
+                Debug.WriteLine("State changed to " + _twain.State + " on thread " + Thread.CurrentThread.ManagedThreadId);
-                //this.BeginInvoke(new Action(() =>
-                //{
-                //    Debug.WriteLine("State change marshaled to thread " + Thread.CurrentThread.ManagedThreadId);
-                //}));
             };
             _twain.DataTransferred += (s, e) =>
             {
                 //this.Invoke(new Action(() =>
                 //{
-                    if (pictureBox1.Image != null)
+                if (pictureBox1.Image != null)
-                    {
+                {
-                        pictureBox1.Image.Dispose();
+                    pictureBox1.Image.Dispose();
-                        pictureBox1.Image = null;
+                    pictureBox1.Image = null;
-                    }
+                }
-                    if (e.NativeData != IntPtr.Zero)
+                if (e.NativeData != IntPtr.Zero)
-                    {
+                {
-                        var img = e.NativeData.GetDrawingBitmap();
+                    var img = e.NativeData.GetDrawingBitmap();
-                        if (img != null)
+                    if (img != null)
-                            pictureBox1.Image = img;
-                    }
-                    else if (!string.IsNullOrEmpty(e.FileDataPath))
-                    {
-                        var img = new Bitmap(e.FileDataPath);
                         pictureBox1.Image = img;
-                    }
+                }
+                else if (!string.IsNullOrEmpty(e.FileDataPath))
+                {
+                    var img = new Bitmap(e.FileDataPath);
+                    pictureBox1.Image = img;
+                }
                 //}));
             };
             _twain.SourceDisabled += (s, e) =>
             {
                 //this.Invoke(new Action(() =>
                 //{
-                    btnStopScan.Enabled = false;
+                btnStopScan.Enabled = false;
-                    btnStartCapture.Enabled = true;
+                btnStartCapture.Enabled = true;
-                    panelOptions.Enabled = true;
+                panelOptions.Enabled = true;
-                    LoadSourceCaps();
+                LoadSourceCaps();
                 //}));
             };
             _twain.TransferReady += (s, e) =>