Fix tiled CCITT decompressor width handling

Use tile width (instead of full image width) when creating T4/T6/Modified Huffman decompressors for tiled TIFF decoding, preventing row-size mismatches and false overrun failures. Also standardize the CCITT overrun error message and add regression coverage for both strip-based and tiled reporter samples that must throw when decoded pixels exceed image width.

src/ImageSharp/Formats/Tiff/Compression/Decompressors/T6TiffCompression.cs

@@ -163,7 +163,7 @@ internal sealed class T6TiffCompression : TiffBaseDecompressor
                     int runLength = (int)bitReader.RunLength;
                     if (runLength > (uint)(scanline.Length - unpacked))
                     {
-                        TiffThrowHelper.ThrowImageFormatException("ccitt compression parsing error");
+                        TiffThrowHelper.ThrowImageFormatException("CCITT compression parsing error: decoded more pixels than the image width.");
                     }
 
                     scanline.Slice(unpacked, runLength).Fill(fillByte);
@@ -175,7 +175,7 @@ internal sealed class T6TiffCompression : TiffBaseDecompressor
                     runLength = (int)bitReader.RunLength;
                     if (runLength > (uint)(scanline.Length - unpacked))
                     {
-                        TiffThrowHelper.ThrowImageFormatException("ccitt compression parsing error");
+                        TiffThrowHelper.ThrowImageFormatException("CCITT compression parsing error: decoded more pixels than the image width.");
                     }
 
                     scanline.Slice(unpacked, runLength).Fill(fillByte);

src/ImageSharp/Formats/Tiff/Compression/TiffDecompressorsFactory.cs

@@ -31,6 +31,10 @@ internal static class TiffDecompressorsFactory
         int tileWidth = 0,
         int tileHeight = 0)
     {
+        // Fax compression emits one decoded row at a time, so tiled images must use
+        // the tile row width that was used to size the caller's destination buffer.
+        int faxWidth = isTiled ? tileWidth : width;
+
         switch (method)
         {
             case TiffDecoderCompressionType.None:
@@ -53,15 +57,15 @@ internal static class TiffDecompressorsFactory
 
             case TiffDecoderCompressionType.T4:
                 DebugGuard.IsTrue(predictor == TiffPredictor.None, "Predictor should only be used with lzw or deflate compression");
-                return new T4TiffCompression(allocator, fillOrder, width, bitsPerPixel, faxOptions, photometricInterpretation);
+                return new T4TiffCompression(allocator, fillOrder, faxWidth, bitsPerPixel, faxOptions, photometricInterpretation);
 
             case TiffDecoderCompressionType.T6:
                 DebugGuard.IsTrue(predictor == TiffPredictor.None, "Predictor should only be used with lzw or deflate compression");
-                return new T6TiffCompression(allocator, fillOrder, width, bitsPerPixel, photometricInterpretation);
+                return new T6TiffCompression(allocator, fillOrder, faxWidth, bitsPerPixel, photometricInterpretation);
 
             case TiffDecoderCompressionType.HuffmanRle:
                 DebugGuard.IsTrue(predictor == TiffPredictor.None, "Predictor should only be used with lzw or deflate compression");
-                return new ModifiedHuffmanTiffCompression(allocator, fillOrder, width, bitsPerPixel, photometricInterpretation);
+                return new ModifiedHuffmanTiffCompression(allocator, fillOrder, faxWidth, bitsPerPixel, photometricInterpretation);
 
             case TiffDecoderCompressionType.Jpeg:
                 DebugGuard.IsTrue(predictor == TiffPredictor.None, "Predictor should only be used with lzw or deflate compression");

src/ImageSharp/Formats/Tiff/TiffDecoderCore.cs

@@ -693,7 +693,7 @@ internal class TiffDecoderCore : ImageDecoderCore
                 tilesBuffers[i] = this.memoryAllocator.Allocate<byte>(uncompressedTilesSize, AllocationOptions.Clean);
             }
 
-            using TiffBaseDecompressor decompressor = this.CreateDecompressor<TPixel>(frame.Width, bitsPerPixel, frame.Metadata);
+            using TiffBaseDecompressor decompressor = this.CreateDecompressor<TPixel>(frame.Width, bitsPerPixel, frame.Metadata, true, tileWidth, tileLength);
             TiffBasePlanarColorDecoder<TPixel> colorDecoder = this.CreatePlanarColorDecoder<TPixel>(frame.Metadata);
 
             int tileIndex = 0;

tests/ImageSharp.Tests/Formats/Tiff/Compression/CcittTiffCompressionTests.cs

@@ -17,22 +17,43 @@ public class CcittTiffCompressionTests
         "H4sICBSogmoCA3BvYy10aWZmLW1oLnRpZgDty7ENgzAQhlEfRBElNKRMnylomSIbZBkWYiTYAFs6RZkhetb7pa84r+urDKW0xa1EraUustu66L/dZ3d19+z2prz/1M0/fx/Z2zsvx2cc" +
         "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA/+jcL3Buw0IBYAEA";
 
+    private const string TiledT4ReporterPocGzipBase64 =
+        "H4sIAAAAAAACCu3UKw7CUBCG0RkuIeC6AxQGj8TwEHWshyWxOhI2QC8Z0QWAIDnNmeQXran4xnEf64jYROQyMvo8RtYepltk++x+rXabblW7P6fZ++fZvtS+T3et/djVR8M2n/Btr1v6C/zCQbQQLUQLRAvRQrRAtBAtRAtEC9FCtEC0EC3+Mlpv/6RrkiQmAAA=";
+
     [Theory]
     [InlineData(T4PocGzipBase64)]
     [InlineData(ModifiedHuffmanPocGzipBase64)]
     public void Decode_CcittStripWithOversizedRun_ThrowsImageFormatException(string gzipBase64)
     {
-        // Keep the reporter's exact TIFF payload compressed so the regression source remains small.
+        using MemoryStream tiffStream = CreateTiffStream(gzipBase64);
+
+        ImageFormatException exception = Assert.Throws<ImageFormatException>(() => Image.Load(tiffStream));
+
+        Assert.Equal("CCITT compression parsing error: decoded more pixels than the image width.", exception.Message);
+    }
+
+    [Fact]
+    public void Decode_TiledCcittReporterSample_ThrowsImageFormatException()
+    {
+        // This is the reporter's exact tiled T4 TIFF sample, gzip-compressed only to keep the test source small.
+        using MemoryStream tiffStream = CreateTiffStream(TiledT4ReporterPocGzipBase64);
+
+        ImageFormatException exception = Assert.Throws<ImageFormatException>(() => Image.Load(tiffStream));
+
+        Assert.Equal("CCITT compression parsing error: decoded more pixels than the image width.", exception.Message);
+    }
+
+    private static MemoryStream CreateTiffStream(string gzipBase64)
+    {
+        // Keep the TIFF payloads compressed so the regression source remains small.
         byte[] compressed = Convert.FromBase64String(gzipBase64);
         using MemoryStream compressedStream = new(compressed);
         using GZipStream gzipStream = new(compressedStream, CompressionMode.Decompress);
-        using MemoryStream tiffStream = new();
+        MemoryStream tiffStream = new();
 
         gzipStream.CopyTo(tiffStream);
         tiffStream.Position = 0;
 
-        ImageFormatException exception = Assert.Throws<ImageFormatException>(() => Image.Load(tiffStream));
-
-        Assert.Equal("CCITT compression parsing error: decoded more pixels than the image width.", exception.Message);
+        return tiffStream;
     }
 }