diff --git a/ArcFormats/Unity/Gx4Lib/ArcDAT.cs b/ArcFormats/Unity/Gx4Lib/ArcDAT.cs
index 2311cad2..d3ef91ee 100644
--- a/ArcFormats/Unity/Gx4Lib/ArcDAT.cs
+++ b/ArcFormats/Unity/Gx4Lib/ArcDAT.cs
@@ -23,6 +23,8 @@
 // IN THE SOFTWARE.
 //
 
+using System;
+using System.Collections.Generic;
 using System.ComponentModel.Composition;
 using System.IO;
 using System.Linq;
@@ -32,6 +34,13 @@ using GameRes.Utility;
 
 namespace GameRes.Formats.Unity.Gx4Lib
 {
+    internal class VisualDiffData
+    {
+        public string   BaseFileName;
+        public int      PosX;
+        public int      PosY;
+    }
+
     [Export(typeof(ArchiveFormat))]
     public class DatOpener : ArchiveFormat
     {
@@ -41,6 +50,8 @@ namespace GameRes.Formats.Unity.Gx4Lib
         public override bool  IsHierarchic { get { return false; } }
         public override bool      CanWrite { get { return false; } }
 
+        Lazy<Dictionary<string, VisualDiffData>>  DefaultVisualMap = new Lazy<Dictionary<string, VisualDiffData>> (ReadVisualData);
+
         public override ArcFile TryOpen (ArcView file)
         {
             uint index_size = file.View.ReadUInt32 (0);
@@ -103,6 +114,25 @@ namespace GameRes.Formats.Unity.Gx4Lib
             int buf_width  = input.ReadInt32();
             int buf_height = input.ReadInt32();
             var info = new ImageMetaData { Width = width, Height = height, BPP = 32 };
+            if (DefaultVisualMap.Value.ContainsKey (entry.Name))
+            {
+                var diff_info = DefaultVisualMap.Value[entry.Name];
+                if (VFS.FileExists (diff_info.BaseFileName))
+                {
+                    var base_entry = VFS.FindFile (diff_info.BaseFileName);
+                    using (var visbase = VFS.OpenImage (base_entry))
+                    {
+                        var base_decoder = visbase as Gx4ImageDecoder;
+                        if (base_decoder != null)
+                        {
+                            info.OffsetX = diff_info.PosX;
+                            info.OffsetY = diff_info.PosY;
+                            var pixels = base_decoder.ReadPixels();
+                            return new Gx4OverlayDecoder (pixels, base_decoder.Info, input, info);
+                        }
+                    }
+                }
+            }
             return new Gx4ImageDecoder (input, info);
         }
 
@@ -204,26 +234,97 @@ namespace GameRes.Formats.Unity.Gx4Lib
                 bits >>= 1;
             }
         }
+
+        internal static Dictionary<string, VisualDiffData> ReadVisualData ()
+        {
+            var map = new Dictionary<string, VisualDiffData>();
+            try
+            {
+                FormatCatalog.Instance.ReadFileList ("gx4_bsz_visual.lst", (line) => {
+                    var parts = line.Split (':', ',');
+                    if (parts.Length > 3)
+                    {
+                        var diff = new VisualDiffData { BaseFileName = parts[1] };
+                        if (int.TryParse (parts[2], out diff.PosX) && int.TryParse (parts[3], out diff.PosY))
+                            map[parts[0]] = diff;
+                    }
+                });
+            }
+            catch { /* ignore errors */ }
+            return map;
+        }
     }
 
     internal class Gx4ImageDecoder : BinaryImageDecoder
     {
+        public int Stride { get; private set; }
+
         public Gx4ImageDecoder (IBinaryStream input, ImageMetaData info) : base (input, info)
         {
+            Stride = (int)info.Width * 4;
         }
 
-        protected override ImageData GetImageData ()
+        public byte[] ReadPixels ()
         {
             m_input.Position = 0x10;
-            int stride = (int)Info.Width * 4;
-            var pixels = m_input.ReadBytes (stride * (int)Info.Height);
+            var pixels = m_input.ReadBytes (Stride * (int)Info.Height);
             for (int i = 0; i < pixels.Length; i += 4)
             {
                 byte t = pixels[i];
                 pixels[i] = pixels[i+2];
                 pixels[i+2] = t;
             }
-            return ImageData.CreateFlipped (Info, PixelFormats.Bgra32, null, pixels, stride);
+            return pixels;
+        }
+
+        protected override ImageData GetImageData ()
+        {
+            var pixels = ReadPixels();
+            return ImageData.CreateFlipped (Info, PixelFormats.Bgra32, null, pixels, Stride);
+        }
+    }
+
+    internal class Gx4OverlayDecoder : BinaryImageDecoder
+    {
+        byte[]      m_pixels;
+
+        ImageMetaData OverlayInfo { get; set; }
+
+        public Gx4OverlayDecoder (byte[] pixels, ImageMetaData info, IBinaryStream input, ImageMetaData overlay_info)
+            : base (input, info)
+        {
+            m_pixels = pixels;
+            OverlayInfo = overlay_info;
+        }
+
+        protected override ImageData GetImageData ()
+        {
+            m_input.Position = 0x10;
+            int base_stride = (int)Info.Width * 4;
+            int diff_stride = (int)OverlayInfo.Width * 4;
+            var diff = m_input.ReadBytes (diff_stride * (int)OverlayInfo.Height);
+            int dst_line = m_pixels.Length - base_stride * (OverlayInfo.OffsetY + 1) + OverlayInfo.OffsetX * 4;
+            int src_line = diff.Length - diff_stride;
+            for (int y = 0; y < (int)OverlayInfo.Height; ++y)
+            {
+                int dst = dst_line;
+                int src = src_line;
+                for (int x = 0; x < (int)OverlayInfo.Width; ++x)
+                {
+                    if (!(0 == diff[src] && 0 == diff[src+1] && 0 == diff[src+2] && 0xFF == diff[src+3]))
+                    {
+                        m_pixels[dst  ] = diff[src+2];
+                        m_pixels[dst+1] = diff[src+1];
+                        m_pixels[dst+2] = diff[src  ];
+                        m_pixels[dst+3] = diff[src+3];
+                    }
+                    dst += 4;
+                    src += 4;
+                }
+                dst_line -= base_stride;
+                src_line -= diff_stride;
+            }
+            return ImageData.CreateFlipped (Info, PixelFormats.Bgra32, null, m_pixels, base_stride);
         }
     }
 }