diff --git a/Legacy/Legacy.csproj b/Legacy/Legacy.csproj
index 06c09e6e..6fd87bfc 100644
--- a/Legacy/Legacy.csproj
+++ b/Legacy/Legacy.csproj
@@ -70,6 +70,7 @@
     <Compile Include="Kurumi\ArcMPK.cs" />
     <Compile Include="Melody\ImageMGO.cs" />
     <Compile Include="Mink\ImageGDF.cs" />
+    <Compile Include="Mutation\ImageRBM.cs" />
     <Compile Include="Nabe\ImageYPF.cs" />
     <Compile Include="Nanami\ArcBMM.cs" />
     <Compile Include="Nekotaro\ArcNSC.cs" />
diff --git a/Legacy/Mutation/ImageRBM.cs b/Legacy/Mutation/ImageRBM.cs
new file mode 100644
index 00000000..57c1bcfe
--- /dev/null
+++ b/Legacy/Mutation/ImageRBM.cs
@@ -0,0 +1,88 @@
+//! \file       ImageRBM.cs
+//! \date       2017 Dec 31
+//! \brief      Mutation compressed image.
+//
+// Copyright (C) 2017 by morkt
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to
+// deal in the Software without restriction, including without limitation the
+// rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+// sell copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+// IN THE SOFTWARE.
+//
+
+using System.ComponentModel.Composition;
+using System.IO;
+using System.Windows.Media;
+using GameRes.Utility;
+
+namespace GameRes.Formats.Mutation
+{
+    [Export(typeof(ImageFormat))]
+    public class RbmFormat : ImageFormat
+    {
+        public override string         Tag { get { return "RBM"; } }
+        public override string Description { get { return "Mutation compressed image"; } }
+        public override uint     Signature { get { return 0x004D4252; } } // 'RBM'
+
+        public override ImageMetaData ReadMetaData (IBinaryStream file)
+        {
+            var header = file.ReadHeader (10);
+            return new ImageMetaData {
+                Width = header.ToUInt16 (6),
+                Height = header.ToUInt16 (8),
+                BPP = 24,
+            };
+        }
+
+        public override ImageData Read (IBinaryStream file, ImageMetaData info)
+        {
+            file.Position = 10;
+            int stride = (int)info.Width * 3;
+            var pixels = new byte[stride * (int)info.Height];
+            int dst = 0;
+            byte bit = 0;
+            byte bit_mask = 0;
+            while (dst < pixels.Length)
+            {
+                bit_mask >>= 1;
+                if (0 == bit_mask)
+                {
+                    bit = file.ReadUInt8();
+                    bit_mask = 0x80;
+                }
+                if (0 != (bit & bit_mask))
+                {
+                    int offset = file.ReadUInt16();
+                    int count = ((offset & 0xF) + 1) * 3;
+                    offset = ((offset >> 4) + 1) * 3;
+                    Binary.CopyOverlapped (pixels, dst-offset, dst, count);
+                    dst += count;
+                }
+                else
+                {
+                    file.Read (pixels, dst, 3);
+                    dst += 3;
+                }
+            }
+            return ImageData.CreateFlipped (info, PixelFormats.Bgr24, null, pixels, stride);
+        }
+
+        public override void Write (Stream file, ImageData image)
+        {
+            throw new System.NotImplementedException ("RbmFormat.Write not implemented");
+        }
+    }
+}