Add support for decoding RLE exr images

src/ImageSharp/Formats/OpenExr/Compression/Compressors/RunLengthCompression.cs

@@ -0,0 +1,94 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+using System.Buffers;
+using SixLabors.ImageSharp.IO;
+using SixLabors.ImageSharp.Memory;
+
+namespace SixLabors.ImageSharp.Formats.OpenExr.Compression.Compressors
+{
+    internal class RunLengthCompression : ExrBaseDecompressor
+    {
+        private readonly IMemoryOwner<byte> tmpBuffer;
+
+        public RunLengthCompression(MemoryAllocator allocator, uint uncompressedBytes)
+            : base(allocator, uncompressedBytes) => this.tmpBuffer = allocator.Allocate<byte>((int)uncompressedBytes);
+
+        public override void Decompress(BufferedReadStream stream, uint compressedBytes, Span<byte> buffer)
+        {
+            Span<byte> uncompressed = this.tmpBuffer.GetSpan();
+            int maxLength = (int)this.UncompressedBytes;
+            int offset = 0;
+            while (compressedBytes > 0)
+            {
+                byte nextByte = ReadNextByte(stream);
+
+                sbyte input = (sbyte)nextByte;
+                if (input < 0)
+                {
+                    int count = -input;
+                    compressedBytes -= (uint)(count + 1);
+
+                    if ((maxLength -= count) < 0)
+                    {
+                        return;
+                    }
+
+                    // Check the input buffer is big enough to contain 'count' bytes of remaining data.
+                    if (compressedBytes < 0)
+                    {
+                        return;
+                    }
+
+                    for (int i = 0; i < count; i++)
+                    {
+                        uncompressed[offset + i] = ReadNextByte(stream);
+                    }
+
+                    offset += count;
+                }
+                else
+                {
+                    int count = input;
+                    byte value = ReadNextByte(stream);
+                    compressedBytes -= 2;
+
+                    if ((maxLength -= count + 1) < 0)
+                    {
+                        return;
+                    }
+
+                    // Check the input buffer is big enough to contain byte to be duplicated.
+                    if (compressedBytes < 0)
+                    {
+                        return;
+                    }
+
+                    for (int i = 0; i < count + 1; i++)
+                    {
+                        uncompressed[offset + i] = value;
+                    }
+
+                    offset += count + 1;
+                }
+            }
+
+            Reconstruct(uncompressed, this.UncompressedBytes);
+            Interleave(uncompressed, this.UncompressedBytes, buffer);
+        }
+
+        private static byte ReadNextByte(BufferedReadStream stream)
+        {
+            int nextByte = stream.ReadByte();
+            if (nextByte == -1)
+            {
+                ExrThrowHelper.ThrowInvalidImageContentException("Not enough data to decompress RLE image!");
+            }
+
+            return (byte)nextByte;
+        }
+
+        protected override void Dispose(bool disposing) => this.tmpBuffer.Dispose();
+    }
+}

src/ImageSharp/Formats/OpenExr/Compression/Compressors/ZipsExrCompression.cs

@@ -19,6 +19,8 @@ namespace SixLabors.ImageSharp.Formats.OpenExr.Compression.Compressors
 
         public override void Decompress(BufferedReadStream stream, uint compressedBytes, Span<byte> buffer)
         {
+            Span<byte> uncompressed = this.tmpBuffer.GetSpan();
+
             long pos = stream.Position;
             using var deframeStream = new ZlibInflateStream(
                        stream,
@@ -30,11 +32,10 @@ namespace SixLabors.ImageSharp.Formats.OpenExr.Compression.Compressors
             deframeStream.AllocateNewBytes((int)this.UncompressedBytes, true);
             DeflateStream dataStream = deframeStream.CompressedStream;
 
-            Span<byte> tmp = this.tmpBuffer.GetSpan();
             int totalRead = 0;
             while (totalRead < buffer.Length)
             {
-                int bytesRead = dataStream.Read(tmp, totalRead, buffer.Length - totalRead);
+                int bytesRead = dataStream.Read(uncompressed, totalRead, buffer.Length - totalRead);
                 if (bytesRead <= 0)
                 {
                     break;
@@ -43,31 +44,8 @@ namespace SixLabors.ImageSharp.Formats.OpenExr.Compression.Compressors
                 totalRead += bytesRead;
             }
 
-            Reconstruct(tmp, this.UncompressedBytes);
-            Interleave(tmp, this.UncompressedBytes, buffer);
-        }
-
-        private static void Reconstruct(Span<byte> buffer, uint unCompressedBytes)
-        {
-            int offset = 0;
-            for (int i = 0; i < unCompressedBytes - 1; i++)
-            {
-                byte d = (byte)(buffer[offset] + (buffer[offset + 1] - 128));
-                buffer[offset + 1] = d;
-                offset++;
-            }
-        }
-
-        private static void Interleave(Span<byte> source, uint unCompressedBytes, Span<byte> output)
-        {
-            int sourceOffset = 0;
-            int offset0 = 0;
-            int offset1 = (int)((unCompressedBytes + 1) / 2);
-            while (sourceOffset < unCompressedBytes)
-            {
-                output[sourceOffset++] = source[offset0++];
-                output[sourceOffset++] = source[offset1++];
-            }
+            Reconstruct(uncompressed, this.UncompressedBytes);
+            Interleave(uncompressed, this.UncompressedBytes, buffer);
         }
 
         protected override void Dispose(bool disposing) => this.tmpBuffer.Dispose();

src/ImageSharp/Formats/OpenExr/Compression/ExrBaseDecompressor.cs

@@ -15,5 +15,28 @@ namespace SixLabors.ImageSharp.Formats.OpenExr.Compression
         }
 
         public abstract void Decompress(BufferedReadStream stream, uint compressedBytes, Span<byte> buffer);
+
+        protected static void Reconstruct(Span<byte> buffer, uint unCompressedBytes)
+        {
+            int offset = 0;
+            for (int i = 0; i < unCompressedBytes - 1; i++)
+            {
+                byte d = (byte)(buffer[offset] + (buffer[offset + 1] - 128));
+                buffer[offset + 1] = d;
+                offset++;
+            }
+        }
+
+        protected static void Interleave(Span<byte> source, uint unCompressedBytes, Span<byte> output)
+        {
+            int sourceOffset = 0;
+            int offset0 = 0;
+            int offset1 = (int)((unCompressedBytes + 1) / 2);
+            while (sourceOffset < unCompressedBytes)
+            {
+                output[sourceOffset++] = source[offset0++];
+                output[sourceOffset++] = source[offset1++];
+            }
+        }
     }
 }

src/ImageSharp/Formats/OpenExr/Compression/ExrDecompressorFactory.cs

@@ -16,6 +16,8 @@ namespace SixLabors.ImageSharp.Formats.OpenExr.Compression
                     return new NoneExrCompression(memoryAllocator, bytesPerRow);
                 case ExrCompressionType.Zips:
                     return new ZipsExrCompression(memoryAllocator, bytesPerRow);
+                case ExrCompressionType.RunLengthEncoded:
+                    return new RunLengthCompression(memoryAllocator, bytesPerRow);
                 default:
                     throw ExrThrowHelper.NotSupportedDecompressor(nameof(method));
             }

src/ImageSharp/Formats/OpenExr/ExrDecoderCore.cs

@@ -9,6 +9,7 @@ using System.Runtime.CompilerServices;
 using System.Text;
 using System.Threading;
 using SixLabors.ImageSharp.Formats.OpenExr.Compression;
+using SixLabors.ImageSharp.Formats.OpenExr.Compression.Compressors;
 using SixLabors.ImageSharp.Formats.Pbm;
 using SixLabors.ImageSharp.IO;
 using SixLabors.ImageSharp.Memory;
@@ -76,7 +77,7 @@ namespace SixLabors.ImageSharp.Formats.OpenExr
         {
             this.ReadExrHeader(stream);
 
-            if (this.Compression is not ExrCompressionType.None and not ExrCompressionType.Zips)
+            if (this.Compression is not ExrCompressionType.None and not ExrCompressionType.Zips and not ExrCompressionType.RunLengthEncoded)
             {
                 ExrThrowHelper.ThrowNotSupported($"Compression {this.Compression} is not yet supported");
             }