Add support for undoing horizontal prediction: Works with deflate, still some issue with lzw

src/ImageSharp/Formats/Tiff/Constants/TiffPlanarConfiguration.cs

@@ -10,11 +10,21 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Constants
     {
         /// <summary>
         /// Chunky format.
+        /// The component values for each pixel are stored contiguously.
+        /// The order of the components within the pixel is specified by
+        /// PhotometricInterpretation. For example, for RGB data, the data is stored as RGBRGBRGB.
         /// </summary>
         Chunky = 1,
 
         /// <summary>
         /// Planar format.
+        /// The components are stored in separate “component planes.” The
+        /// values in StripOffsets and StripByteCounts are then arranged as a 2-dimensional
+        /// array, with SamplesPerPixel rows and StripsPerImage columns. (All of the columns
+        /// for row 0 are stored first, followed by the columns of row 1, and so on.)
+        /// PhotometricInterpretation describes the type of data stored in each component
+        /// plane. For example, RGB data is stored with the Red components in one component
+        /// plane, the Green in another, and the Blue in another.
         /// </summary>
         Planar = 2
     }

src/ImageSharp/Formats/Tiff/README.md

@@ -25,6 +25,15 @@
 
 ## Implementation Status
 
+### 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.
+
+Encoder:
+- Encoding image with a palette have a difference of 0.0043% to the ReferenceDecoder (ImageMagick)
+
 ### Deviations from the TIFF spec (to be fixed)
 
 - Decoder

src/ImageSharp/Formats/Tiff/TiffDecoderCore.cs

@@ -240,6 +240,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff
             var coreMetadata = new ImageFrameMetadata();
             frameMetaData = coreMetadata.GetTiffMetadata();
             frameMetaData.Tags = tags;
+            TiffFrameMetadata tiffFormatMetaData = coreMetadata.GetFormatMetadata(TiffFormat.Instance);
 
             this.VerifyAndParseOptions(frameMetaData);
 
@@ -260,9 +261,38 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                 this.DecodeStripsChunky(frame, rowsPerStrip, stripOffsets, stripByteCounts, width);
             }
 
+            if (tiffFormatMetaData.Predictor == TiffPredictor.Horizontal)
+            {
+                this.UndoHorizontalPredictor(width, height, frame);
+            }
+
             return frame;
         }
 
+        private void UndoHorizontalPredictor<TPixel>(int width, int height, ImageFrame<TPixel> frame)
+            where TPixel : unmanaged, IPixel<TPixel>
+        {
+            using System.Buffers.IMemoryOwner<Rgb24> rowRgbBuffer = this.memoryAllocator.Allocate<Rgb24>(width);
+            System.Span<Rgb24> rowRgb = rowRgbBuffer.GetSpan();
+            for (int y = 0; y < height; y++)
+            {
+                System.Span<TPixel> pixelRow = frame.GetPixelRowSpan(y);
+                PixelOperations<TPixel>.Instance.ToRgb24(this.configuration, pixelRow, rowRgb);
+                byte r = rowRgb[0].R;
+                byte g = rowRgb[0].G;
+                byte b = rowRgb[0].B;
+                for (int x = 1; x < width; x++)
+                {
+                    ref TPixel pixel = ref pixelRow[x];
+                    r += rowRgb[x].R;
+                    g += rowRgb[x].G;
+                    b += rowRgb[x].B;
+                    var rgb = new Rgb24(r, g, b);
+                    pixel.FromRgb24(rgb);
+                }
+            }
+        }
+
         /// <summary>
         /// Calculates the size (in bytes) for a pixel buffer using the determined color format.
         /// </summary>

src/ImageSharp/Formats/Tiff/TiffDecoderHelpers.cs

@@ -106,9 +106,9 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                 TiffThrowHelper.ThrowNotSupported("The Tile images is not supported.");
             }
 
-            if (entries.Predictor != TiffPredictor.None)
+            if (entries.Predictor == TiffPredictor.FloatingPoint)
             {
-                TiffThrowHelper.ThrowNotSupported("At the moment we support only None Predictor images.");
+                TiffThrowHelper.ThrowNotSupported("ImageSharp does not support FloatingPoint Predictor images.");
             }
 
             if (entries.SampleFormat != null)
@@ -117,7 +117,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                 {
                     if (format != TiffSampleFormat.UnsignedInteger)
                     {
-                        TiffThrowHelper.ThrowNotSupported("At the moment support only UnsignedInteger SampleFormat.");
+                        TiffThrowHelper.ThrowNotSupported("ImageSharp only supports the UnsignedInteger SampleFormat.");
                     }
                 }
             }

tests/ImageSharp.Tests/TestImages.cs

@@ -529,7 +529,7 @@ namespace SixLabors.ImageSharp.Tests
             public const string RgbDeflate_Predictor = "Tiff/rgb_deflate.tiff";
             public const string RgbDeflateMultistrip = "Tiff/rgb_deflate_multistrip.tiff";
             public const string RgbJpeg = "Tiff/rgb_jpeg.tiff";
-            public const string RgbLzw_Predictor = "Tiff/rgb_lzw.tiff";
+            public const string RgbLzw_Predictor = "Tiff/rgb_lzw_predictor.tiff";
             public const string RgbLzw_NoPredictor_Multistrip = "Tiff/rgb_lzw_noPredictor_multistrip.tiff";
             public const string RgbLzw_NoPredictor_Multistrip_Motorola = "Tiff/rgb_lzw_noPredictor_multistrip_Motorola.tiff";
             public const string RgbLzw_NoPredictor_Singlestrip_Motorola = "Tiff/rgb_lzw_noPredictor_singlestrip_Motorola.tiff";
@@ -553,10 +553,12 @@ namespace SixLabors.ImageSharp.Tests
 
             public static readonly string[] All =
             {
-                Calliphora_PaletteUncompressed, /*Calliphora_RgbDeflate_Predictor, Calliphora_RgbLzwe_Predictor, */ Calliphora_RgbPackbits,
+                Calliphora_PaletteUncompressed, Calliphora_RgbPackbits,
+                Calliphora_GrayscaleDeflate_Predictor, Calliphora_RgbDeflate_Predictor, RgbDeflate_Predictor,
+                Calliphora_RgbLzw_Predictor, RgbLzw_Predictor, // 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,
-                GrayscaleUncompressed, PaletteDeflateMultistrip, PaletteUncompressed, /*RgbDeflate_Predictor,*/ RgbDeflateMultistrip, /*RgbJpeg,*/ /*RgbLzw_Predictor, RgbLzwMultistrip_Predictor,*/
+                GrayscaleUncompressed, PaletteDeflateMultistrip, PaletteUncompressed, RgbDeflateMultistrip, /*RgbJpeg,*/ /* RgbLzwMultistrip_Predictor,*/
                 RgbLzw_NoPredictor_Multistrip, RgbLzw_NoPredictor_Multistrip_Motorola, RgbLzw_NoPredictor_Singlestrip_Motorola, RgbPackbits, RgbPackbitsMultistrip, RgbUncompressed,
                 /* MultiframeLzw_Predictor, MultiFrameDifferentVariants, SampleMetadata,*/ SmallRgbDeflate, SmallRgbLzw,
             };
@@ -565,7 +567,7 @@ namespace SixLabors.ImageSharp.Tests
 
             public static readonly string[] Metadata = { SampleMetadata };
 
-            public static readonly string[] NotSupported = { Calliphora_GrayscaleDeflate_Predictor, Calliphora_RgbJpeg, Calliphora_RgbDeflate_Predictor, Calliphora_RgbLzw_Predictor, RgbDeflate_Predictor, RgbLzw_Predictor, RgbLzwMultistrip_Predictor, RgbJpeg, RgbUncompressedTiled, MultiframeLzw_Predictor, MultiframeDifferentSize, MultiframeDifferentVariants };
+            public static readonly string[] NotSupported = { Calliphora_RgbJpeg, RgbLzwMultistrip_Predictor, RgbJpeg, RgbUncompressedTiled, MultiframeLzw_Predictor, MultiframeDifferentSize, MultiframeDifferentVariants };
         }
     }
 }