diff --git a/ArcFormats/ArcFormats.csproj b/ArcFormats/ArcFormats.csproj
index 666fae686..64fbc3d52 100644
--- a/ArcFormats/ArcFormats.csproj
+++ b/ArcFormats/ArcFormats.csproj
@@ -280,6 +280,7 @@
+
diff --git a/ArcFormats/YuRis/ImageYDG.cs b/ArcFormats/YuRis/ImageYDG.cs
new file mode 100644
index 000000000..31eb66e90
--- /dev/null
+++ b/ArcFormats/YuRis/ImageYDG.cs
@@ -0,0 +1,359 @@
+//! \file ImageYDG.cs
+//! \date Sun Apr 12 15:08:10 2026
+//! \brief YU-RIS compressed image.
+//
+// Copyright (C) 2026 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;
+using System.ComponentModel;
+using System.ComponentModel.Composition;
+using System.IO;
+using System.Reflection;
+using System.Runtime.InteropServices;
+using System.Windows.Media;
+using GameRes.Utility;
+
+namespace GameRes.Formats.YuRis
+{
+ internal class YdgMetaData : ImageMetaData
+ {
+ public int HeaderLength;
+ }
+
+ internal class YdgTile
+ {
+ public uint Offset;
+ public uint Size;
+ public ushort X;
+ public ushort Height;
+ }
+
+ [Export(typeof(ImageFormat))]
+ public class YdgFormat : ImageFormat
+ {
+ public override string Tag { get { return "YDG"; } }
+ public override string Description { get { return "YU-RIS compressed image format"; } }
+ public override uint Signature { get { return 0x00474459; } } // 'YDG\0'
+
+ public YdgFormat()
+ {
+ Extensions = new string[] { "ydg" };
+ }
+
+ public override ImageMetaData ReadMetaData (IBinaryStream stream)
+ {
+ var header = stream.ReadHeader (0x30);
+ if (!header.AsciiEqual ("YDG\0"))
+ return null;
+ if (!header.AsciiEqual (4, "YU-RIS"))
+ return null;
+
+ return new YdgMetaData
+ {
+ Width = header.ToUInt16 (0x20),
+ Height = header.ToUInt16 (0x22),
+ BPP = 32,
+ HeaderLength = header.ToInt32 (0x10),
+ };
+ }
+
+ public override ImageData Read (IBinaryStream stream, ImageMetaData info)
+ {
+ var reader = new YdgReader(stream, (YdgMetaData)info);
+ reader.Unpack();
+ return ImageData.Create (info, reader.Format, null, reader.Data);
+ }
+
+ public override void Write (Stream file, ImageData image)
+ {
+ throw new NotImplementedException ("YdgFormat.Write not implemented");
+ }
+ }
+
+ internal sealed class YdgReader
+ {
+ IBinaryStream m_input;
+ YdgMetaData m_info;
+
+ public PixelFormat Format { get; private set; }
+ public byte[] Data { get { return m_output; } }
+
+ public YdgReader(IBinaryStream input, YdgMetaData info)
+ {
+ m_input = input;
+ m_info = info;
+ m_output = new byte[4 * (int)info.Width * (int)info.Height];
+ Format = PixelFormats.Bgra32;
+ }
+ byte[] m_output;
+
+ public void Unpack ()
+ {
+ var tiles = ReadIndex ();
+ int width = (int)m_info.Width;
+ int height = (int)m_info.Height;
+ int dst_y = 0;
+ foreach (var tile in tiles)
+ {
+ byte[] pixels = ReadTile (tile, out width, out height);
+
+ int tile_height = Math.Min(height, tile.Height);
+ CopyTile (pixels, width, tile_height, tile.X, dst_y);
+ dst_y += tile_height;
+ if (dst_y >= m_info.Height)
+ break;
+ }
+ }
+
+ YdgTile[] ReadIndex ()
+ {
+ m_input.Position = m_info.HeaderLength;
+ int tileCount = m_input.ReadInt32();
+ var dir = new YdgTile[tileCount];
+ for (int i = 0; i < dir.Length; ++i)
+ {
+ dir[i] = new YdgTile
+ {
+ Offset = m_input.ReadUInt32(),
+ Size = m_input.ReadUInt32(),
+ X = m_input.ReadUInt16(),
+ Height = m_input.ReadUInt16(),
+ };
+ m_input.ReadUInt32();
+ }
+ return dir;
+ }
+
+ byte[] ReadTile (YdgTile tile, out int width, out int height)
+ {
+ m_input.Position = tile.Offset;
+ var data = m_input.ReadBytes ((int)tile.Size);
+ if (Binary.AsciiEqual (data, 0, "RIFF") && Binary.AsciiEqual (data, 8, "WEBP"))
+ return DecodeWebP (data, out width, out height);
+ return DecodeQoi (data, out width, out height);
+ }
+
+ void CopyTile (byte[] pixels, int src_width, int src_height, int dst_x, int dst_y)
+ {
+ int copy_width = Math.Min (src_width, (int)m_info.Width - dst_x);
+ int copy_height = Math.Min (src_height, (int)m_info.Height - dst_y);
+ if (copy_width <= 0 || copy_height <= 0)
+ return;
+
+ int src_stride = src_width * 4;
+ int dst_stride = (int)m_info.Width * 4;
+ int dst = dst_y * dst_stride + dst_x * 4;
+ int row_bytes = copy_width * 4;
+ int src = 0;
+ for (int y = 0; y < copy_height; ++y)
+ {
+ Buffer.BlockCopy (pixels, src, m_output, dst, row_bytes);
+ src += src_stride;
+ dst += dst_stride;
+ }
+ }
+
+ byte[] DecodeWebP (byte[] data, out int width, out int height)
+ {
+ LibWebPLoader.Load ();
+
+ width = 0;
+ height = 0;
+ if (1 != WebPGetInfo (data, (UIntPtr)data.Length, ref width, ref height))
+ throw new InvalidFormatException ("WebP image decoder failed.");
+
+ int stride = width * 4;
+ var output = new byte[stride * height];
+ var handle = GCHandle.Alloc (output, GCHandleType.Pinned);
+ try
+ {
+ if (IntPtr.Zero == WebPDecodeBGRAInto (data, (UIntPtr)data.Length,
+ handle.AddrOfPinnedObject (), (UIntPtr)output.Length, stride))
+ {
+ throw new InvalidFormatException ("WebP image decoder failed.");
+ }
+ }
+ finally
+ {
+ handle.Free ();
+ }
+ return output;
+ }
+
+ byte[] DecodeQoi(byte[] data, out int width, out int height)
+ {
+ using (var input = new BinMemoryStream(data))
+ {
+ if (0x66696F71 != input.ReadInt32()) // "qoif"
+ throw new InvalidFormatException ("Invalid QOI signature");
+
+ width = (int)Binary.BigEndian(input.ReadUInt32());
+ height = (int)Binary.BigEndian(input.ReadUInt32());
+ int channels = input.ReadByte();
+ int colorspace = input.ReadByte();
+ var count = 4 * width * height;
+ var output = new byte[count];
+ var qoi = new QoiDecodeStream(input);
+ uint pixel = 0;
+ var run = 0;
+ var dst = 0;
+ while (dst < count)
+ {
+ if (run > 1)
+ --run;
+ else
+ {
+ run = qoi.Read (out pixel);
+ }
+ output[dst ] = (byte)pixel;
+ output[dst + 1] = (byte)(pixel >> 8);
+ output[dst + 2] = (byte)(pixel >> 16);
+ output[dst + 3] = (byte)(pixel >> 24);
+ dst += 4;
+ }
+ return output;
+ }
+ }
+
+ static class QoiCodec
+ {
+ public const int Index = 0x00;
+ public const int Diff = 0x40;
+ public const int Luma = 0x80;
+ public const int Run = 0xC0;
+ public const int Rgb = 0xFE;
+ public const int Rgba = 0xFF;
+ public const int Mask2 = 0xC0;
+ public const int HashTableSize = 64;
+ }
+
+ class QoiDecodeStream
+ {
+ readonly IBinaryStream m_input;
+ readonly byte[] m_table;
+ uint m_pixel;
+
+ public QoiDecodeStream(IBinaryStream input)
+ {
+ m_input = input;
+ m_table = new byte[4 * QoiCodec.HashTableSize];
+ m_pixel = 0xFF000000;
+ }
+
+ public int Read(out uint output)
+ {
+ var r = (byte)m_pixel;
+ var g = (byte)(m_pixel >> 8);
+ var b = (byte)(m_pixel >> 16);
+ var a = (byte)(m_pixel >> 24);
+ var run = 1;
+ var b1 = m_input.ReadByte();
+ if (-1 == b1)
+ throw new EndOfStreamException();
+
+ if (QoiCodec.Rgb == b1)
+ {
+ var rgb = m_input.ReadInt24();
+ r = (byte)rgb;
+ g = (byte)(rgb >> 8);
+ b = (byte)(rgb >> 16);
+ }
+ else if (QoiCodec.Rgba == b1)
+ {
+ var rgba = m_input.ReadInt32();
+ r = (byte)rgba;
+ g = (byte)(rgba >> 8);
+ b = (byte)(rgba >> 16);
+ a = (byte)(rgba >> 24);
+ }
+ else if (QoiCodec.Index == (b1 & QoiCodec.Mask2))
+ {
+ var p1 = (b1 & ~QoiCodec.Mask2) * 4;
+ r = m_table[p1];
+ g = m_table[p1 + 1];
+ b = m_table[p1 + 2];
+ a = m_table[p1 + 3];
+ }
+ else if (QoiCodec.Diff == (b1 & QoiCodec.Mask2))
+ {
+ r += (byte)(((b1 >> 4) & 0x03) - 2);
+ g += (byte)(((b1 >> 2) & 0x03) - 2);
+ b += (byte)((b1 & 0x03) - 2);
+ }
+ else if (QoiCodec.Luma == (b1 & QoiCodec.Mask2))
+ {
+ var b2 = m_input.ReadByte();
+ if (-1 == b2)
+ throw new EndOfStreamException();
+ var vg = (b1 & 0x3F) - 32;
+ r += (byte)(vg - 8 + ((b2 >> 4) & 0x0F));
+ g += (byte)vg;
+ b += (byte)(vg - 8 + (b2 & 0x0F));
+ }
+ else if (QoiCodec.Run == (b1 & QoiCodec.Mask2))
+ {
+ run = (b1 & 0x3F) + 1;
+ }
+
+ var p2 = (r * 3 + g * 5 + b * 7 + a * 11) % QoiCodec.HashTableSize * 4;
+ m_table[p2 ] = r;
+ m_table[p2 + 1] = g;
+ m_table[p2 + 2] = b;
+ m_table[p2 + 3] = a;
+ m_pixel = (uint)(r | (g << 8) | (b << 16) | (a << 24));
+ output = (uint)(b | (g << 8) | (r << 16) | (a << 24));
+ return run;
+ }
+ }
+
+ [DllImport("libwebp.dll", EntryPoint = "WebPGetInfo", CallingConvention = CallingConvention.Cdecl)]
+ public static extern int WebPGetInfo([MarshalAs(UnmanagedType.LPArray)] byte[] data, UIntPtr data_size, ref int width, ref int height);
+
+ [DllImport("libwebp.dll", EntryPoint = "WebPDecodeBGRAInto", CallingConvention = CallingConvention.Cdecl)]
+ public static extern IntPtr WebPDecodeBGRAInto([MarshalAs(UnmanagedType.LPArray)] byte[] data, UIntPtr data_size, IntPtr output_buffer, UIntPtr output_buffer_size, int output_stride);
+ }
+
+ internal static class LibWebPLoader
+ {
+ [DllImport("kernel32.dll", SetLastError = true, CallingConvention = CallingConvention.StdCall)]
+ static extern IntPtr LoadLibraryEx(string lpFileName, IntPtr hReservedNull, uint dwFlags);
+
+ static bool loaded = false;
+
+ const uint LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR = 0x00000100;
+ const uint LOAD_LIBRARY_SEARCH_SYSTEM32 = 0x00000800;
+
+ public static void Load()
+ {
+ if (loaded)
+ return;
+ var folder = Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location);
+ folder = Path.Combine(folder, (IntPtr.Size == 4) ? "x86" : "x64");
+ var fullPath = Path.Combine(folder, "libwebp.dll");
+ fullPath = Path.GetFullPath(fullPath);
+ var handle = LoadLibraryEx(fullPath, IntPtr.Zero, LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR | LOAD_LIBRARY_SEARCH_SYSTEM32);
+ if (IntPtr.Zero == handle)
+ throw new Win32Exception(Marshal.GetLastWin32Error());
+ loaded = true;
+ }
+ }
+}