Fix issue with huffman RLE where last bits of a row could get ignored

src/ImageSharp/Formats/Tiff/Compression/T4BitReader.cs

@@ -253,7 +253,18 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff.Compression
         /// <summary>
         /// Gets a value indicating whether there is more data to read left.
         /// </summary>
-        public bool HasMoreData => this.position < (ulong)this.dataLength - 1;
+        public bool HasMoreData
+        {
+            get
+            {
+                if (this.isModifiedHuffmanRle)
+                {
+                    return this.position < (ulong)this.dataLength - 1 || (this.bitsRead > 0 && this.bitsRead < 7);
+                }
+
+                return this.position < (ulong)this.dataLength - 1;
+            }
+        }
 
         /// <summary>
         /// Gets a value indicating whether the current run is a white pixel run, otherwise its a black pixel run.
@@ -381,10 +392,7 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff.Compression
         }
 
         /// <inheritdoc/>
-        public void Dispose()
-        {
-            this.Data.Dispose();
-        }
+        public void Dispose() => this.Data.Dispose();
 
         private uint WhiteTerminatingCodeRunLength()
         {

src/ImageSharp/Formats/Tiff/README.md

@@ -28,8 +28,7 @@
 ### Know issue which need to be fixed
 
 Decoder:
-- Decoding HUffman RLE for `Calliphora_huffman_rle.tiff` has 4 pixels difference to the reference decoder. Al those are at the very edge of the image (reason unknown so far).
-- Decoding compressed images with HorizontalPrediction: Works for deflate, but not for lzw.
+- Decoding compressed images with HorizontalPrediction: Works for deflate, but not for lzw (maybe an issue with lzw itself?).
 
 ### Deviations from the TIFF spec (to be fixed)
 

tests/ImageSharp.Tests/TestImages.cs

@@ -522,6 +522,9 @@ namespace SixLabors.ImageSharp.Tests
             public const string HuffmanRleAllTermCodes = "Tiff/huffman_rle_all_terminating_codes.tiff";
             public const string HuffmanRleAllMakeupCodes = "Tiff/huffman_rle_all_makeup_codes.tiff";
 
+            // Test case for an issue, that the last bits in a row got ignored.
+            public const string HuffmanRle_basi3p02 = "Tiff/basi3p02_huffman_rle.tiff";
+
             public const string GrayscaleDeflateMultistrip = "Tiff/grayscale_deflate_multistrip.tiff";
             public const string GrayscaleUncompressed = "Tiff/grayscale_uncompressed.tiff";
             public const string PaletteDeflateMultistrip = "Tiff/palette_grayscale_deflate_multistrip.tiff";
@@ -558,7 +561,7 @@ namespace SixLabors.ImageSharp.Tests
                 Calliphora_GrayscaleDeflate_Predictor, Calliphora_RgbDeflate_Predictor, RgbDeflatePredictor,
                 Calliphora_RgbLzw_Predictor, RgbLzwPredictor, // TODO: Undoing the horizontal prediction seems to fail for lzw. Do we need to do something different for lzw?
                 Calliphora_BiColor, Calliphora_RgbUncompressed, Calliphora_HuffmanCompressed, Calliphora_Fax3Compressed, CcittFax3AllTermCodes, CcittFax3AllMakeupCodes,
-                HuffmanRleAllTermCodes, HuffmanRleAllMakeupCodes, GrayscaleDeflateMultistrip, Calliphora_GrayscaleDeflate, Calliphora_GrayscaleUncompressed,
+                HuffmanRleAllTermCodes, HuffmanRleAllMakeupCodes, HuffmanRle_basi3p02, GrayscaleDeflateMultistrip, Calliphora_GrayscaleDeflate, Calliphora_GrayscaleUncompressed,
                 GrayscaleUncompressed, PaletteDeflateMultistrip, PaletteUncompressed, RgbDeflateMultistrip, /*RgbJpeg,*/ /* RgbLzwMultistrip_Predictor,*/
                 RgbLzwNoPredictorMultistrip, RgbLzwNoPredictorMultistripMotorola, RgbLzwNoPredictorSinglestripMotorola, RgbPackbits, RgbPackbitsMultistrip, RgbUncompressed,
                 /* MultiframeLzw_Predictor, MultiFrameDifferentVariants, SampleMetadata,*/ SmallRgbDeflate, SmallRgbLzw, RgbLzwNoPredictor

tests/Images/Input/Tiff/basi3p02_huffman_rle.tiff

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:af20deb1b64cac3272b6560565cb01f28247b9fd8b6d5a86eafbe7b0aea27d48
+size 340