Add option to encode Tiff's with jpeg compression

src/ImageSharp/Formats/Tiff/Compression/Compressors/PackBitsWriter.cs

@@ -80,7 +80,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Compression.Compressors
         private static bool IsReplicateRun(ReadOnlySpan<byte> rowSpan, int startPos)
         {
             // We consider run which has at least 3 same consecutive bytes a candidate for a run.
-            var startByte = rowSpan[startPos];
+            byte startByte = rowSpan[startPos];
             int count = 0;
             for (int i = startPos + 1; i < rowSpan.Length; i++)
             {

src/ImageSharp/Formats/Tiff/Compression/Compressors/TiffJpegCompressor.cs

@@ -0,0 +1,49 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+using System.IO;
+using SixLabors.ImageSharp.Formats.Jpeg;
+using SixLabors.ImageSharp.Formats.Tiff.Constants;
+using SixLabors.ImageSharp.Memory;
+using SixLabors.ImageSharp.PixelFormats;
+
+namespace SixLabors.ImageSharp.Formats.Tiff.Compression.Compressors
+{
+    internal class TiffJpegCompressor : TiffBaseCompressor
+    {
+        public TiffJpegCompressor(Stream output, MemoryAllocator memoryAllocator, int width, int bitsPerPixel, TiffPredictor predictor = TiffPredictor.None)
+            : base(output, memoryAllocator, width, bitsPerPixel, predictor)
+        {
+        }
+
+        /// <inheritdoc/>
+        public override TiffCompression Method => TiffCompression.Jpeg;
+
+        /// <inheritdoc/>
+        public override void Initialize(int rowsPerStrip)
+        {
+        }
+
+        /// <inheritdoc/>
+        public override void CompressStrip(Span<byte> rows, int height)
+        {
+            int pixelCount = rows.Length / 3;
+            int width = pixelCount / height;
+
+            using var memoryStream = new MemoryStream();
+            var image = Image.LoadPixelData<Rgb24>(rows, width, height);
+            image.Save(memoryStream, new JpegEncoder()
+            {
+                Subsample = JpegSubsample.Rgb
+            });
+            memoryStream.Position = 0;
+            memoryStream.WriteTo(this.Output);
+        }
+
+        /// <inheritdoc/>
+        protected override void Dispose(bool disposing)
+        {
+        }
+    }
+}

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

@@ -25,7 +25,6 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Compression
                 // The following compression types are not implemented in the encoder and will default to no compression instead.
                 case TiffCompression.ItuTRecT43:
                 case TiffCompression.ItuTRecT82:
-                case TiffCompression.Jpeg:
                 case TiffCompression.OldJpeg:
                 case TiffCompression.OldDeflate:
                 case TiffCompression.None:
@@ -34,6 +33,11 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Compression
 
                     return new NoCompressor(output, allocator, width, bitsPerPixel);
 
+                case TiffCompression.Jpeg:
+                    DebugGuard.IsTrue(compressionLevel == DeflateCompressionLevel.DefaultCompression, "No deflate compression level is expected to be set");
+                    DebugGuard.IsTrue(predictor == TiffPredictor.None, "Predictor should only be used with lzw or deflate compression");
+                    return new TiffJpegCompressor(output, allocator, width, bitsPerPixel);
+
                 case TiffCompression.PackBits:
                     DebugGuard.IsTrue(compressionLevel == DeflateCompressionLevel.DefaultCompression, "No deflate compression level is expected to be set");
                     DebugGuard.IsTrue(predictor == TiffPredictor.None, "Predictor should only be used with lzw or deflate compression");

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

@@ -20,7 +20,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Compression
             TiffColorType colorType,
             TiffPredictor predictor,
             FaxCompressionOptions faxOptions,
-			byte[] jpegTables,
+            byte[] jpegTables,
             TiffFillOrder fillOrder,
             ByteOrder byteOrder)
         {

src/ImageSharp/Formats/Tiff/TiffDecoderCore.cs

@@ -366,7 +366,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                 this.ColorType,
                 this.Predictor,
                 this.FaxCompressionOptions,
-				this.JpegTables,
+                this.JpegTables,
                 this.FillOrder,
                 this.byteOrder);
 

src/ImageSharp/Formats/Tiff/TiffEncoderEntriesCollector.cs

@@ -396,6 +396,9 @@ namespace SixLabors.ImageSharp.Formats.Tiff
 
                     case TiffCompression.Ccitt1D:
                         return (ushort)TiffCompression.Ccitt1D;
+
+                    case TiffCompression.Jpeg:
+                        return (ushort)TiffCompression.Jpeg;
                 }
 
                 return (ushort)TiffCompression.None;

tests/ImageSharp.Tests/Formats/Tiff/TiffEncoderTests.cs

@@ -114,7 +114,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tiff
         [InlineData(TiffPhotometricInterpretation.BlackIsZero, TiffCompression.Ccitt1D, TiffBitsPerPixel.Bit1, TiffCompression.Ccitt1D)]
         [InlineData(TiffPhotometricInterpretation.Rgb, TiffCompression.ItuTRecT43, TiffBitsPerPixel.Bit24, TiffCompression.None)]
         [InlineData(TiffPhotometricInterpretation.Rgb, TiffCompression.ItuTRecT82, TiffBitsPerPixel.Bit24, TiffCompression.None)]
-        [InlineData(TiffPhotometricInterpretation.Rgb, TiffCompression.Jpeg, TiffBitsPerPixel.Bit24, TiffCompression.None)]
+        [InlineData(TiffPhotometricInterpretation.Rgb, TiffCompression.Jpeg, TiffBitsPerPixel.Bit24, TiffCompression.Jpeg)]
         [InlineData(TiffPhotometricInterpretation.Rgb, TiffCompression.OldDeflate, TiffBitsPerPixel.Bit24, TiffCompression.None)]
         [InlineData(TiffPhotometricInterpretation.Rgb, TiffCompression.OldJpeg, TiffBitsPerPixel.Bit24, TiffCompression.None)]
         public void EncoderOptions_SetPhotometricInterpretationAndCompression_Works(
@@ -288,6 +288,11 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tiff
         public void TiffEncoder_EncodeRgb_WithPackBitsCompression_Works<TPixel>(TestImageProvider<TPixel> provider)
             where TPixel : unmanaged, IPixel<TPixel> => TestTiffEncoderCore(provider, TiffBitsPerPixel.Bit24, TiffPhotometricInterpretation.Rgb, TiffCompression.PackBits);
 
+        [Theory]
+        [WithFile(Calliphora_RgbUncompressed, PixelTypes.Rgba32)]
+        public void TiffEncoder_EncodeRgb_WithjpegCompression_Works<TPixel>(TestImageProvider<TPixel> provider)
+            where TPixel : unmanaged, IPixel<TPixel> => TestTiffEncoderCore(provider, TiffBitsPerPixel.Bit24, TiffPhotometricInterpretation.Rgb, TiffCompression.Jpeg);
+
         [Theory]
         [WithFile(Calliphora_GrayscaleUncompressed, PixelTypes.Rgba32)]
         public void TiffEncoder_EncodeGray_Works<TPixel>(TestImageProvider<TPixel> provider)