Small bug fixes, ready for merging

src/ImageSharp/Formats/Jpeg/Components/Decoder/ArithmeticScanDecoder.cs

@@ -247,8 +247,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
 
             this.scanBuffer = new JpegBitReader(this.stream);
 
-            bool fullScan = this.frame.Progressive || this.frame.MultiScan;
-            this.frame.AllocateComponents(fullScan);
+            this.frame.AllocateComponents();
 
             if (this.frame.Progressive)
             {
@@ -326,11 +325,13 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
 
             if (this.scanComponentCount != 1)
             {
+                this.spectralConverter.PrepareForDecoding();
                 this.ParseBaselineDataInterleaved();
                 this.spectralConverter.CommitConversion();
             }
             else if (this.frame.ComponentCount == 1)
             {
+                this.spectralConverter.PrepareForDecoding();
                 this.ParseBaselineDataSingleComponent();
                 this.spectralConverter.CommitConversion();
             }

src/ImageSharp/Formats/Jpeg/Components/Decoder/HuffmanScanDecoder.cs

@@ -109,13 +109,8 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
         // The successive approximation low bit end.
         public int SuccessiveLow { get; set; }
 
-        /// <summary>
-        /// Decodes the entropy coded data.
-        /// </summary>
-        /// <param name="scanComponentCount">Component count in the current scan.</param>
-        /// <param name="frame">Frame containing decoding data about the frame.</param>
-        /// <param name="jpegData">Decoding data about the jpeg.</param>
-        public void ParseEntropyCodedData(int scanComponentCount, JpegFrame frame, IRawJpegData jpegData)
+        /// <inheritdoc/>
+        public void ParseEntropyCodedData(int scanComponentCount)
         {
             this.cancellationToken.ThrowIfCancellationRequested();
 
@@ -123,17 +118,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
 
             this.scanBuffer = new JpegBitReader(this.stream);
 
-            // Decoder can encounter markers which would alter parameters
-            // needed for spectral buffers allocation and for spectral
-            // converter allocation
-            if (this.frame == null)
-            {
-                frame.AllocateComponents();
-
-                this.frame = frame;
-                this.components = frame.Components;
-                this.spectralConverter.InjectFrameData(frame, jpegData);
-            }
+            this.frame.AllocateComponents();
 
             if (!this.frame.Progressive)
             {
@@ -163,11 +148,13 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
         {
             if (this.scanComponentCount != 1)
             {
+                this.spectralConverter.PrepareForDecoding();
                 this.ParseBaselineDataInterleaved();
                 this.spectralConverter.CommitConversion();
             }
             else if (this.frame.ComponentCount == 1)
             {
+                this.spectralConverter.PrepareForDecoding();
                 this.ParseBaselineDataSingleComponent();
                 this.spectralConverter.CommitConversion();
             }
@@ -280,7 +267,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
 
         private void ParseBaselineDataSingleComponent()
         {
-            var component = this.frame.Components[0] as JpegComponent;
+            JpegComponent component = this.frame.Components[0];
             int mcuLines = this.frame.McusPerColumn;
             int w = component.WidthInBlocks;
             int h = component.SamplingFactors.Height;

src/ImageSharp/Formats/Jpeg/Components/Decoder/SpectralConverter.cs

@@ -35,12 +35,19 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
         /// Injects jpeg image decoding metadata.
         /// </summary>
         /// <remarks>
-        /// This is guaranteed to be called only once at SOF marker by <see cref="HuffmanScanDecoder"/>.
+        /// This should be called exactly once during SOF (Start Of Frame) marker.
         /// </remarks>
-        /// <param name="frame"><see cref="JpegFrame"/> instance containing decoder-specific parameters.</param>
-        /// <param name="jpegData"><see cref="IRawJpegData"/> instance containing decoder-specific parameters.</param>
+        /// <param name="frame"><see cref="JpegFrame"/>Instance containing decoder-specific parameters.</param>
+        /// <param name="jpegData"><see cref="IRawJpegData"/>Instance containing decoder-specific parameters.</param>
         public abstract void InjectFrameData(JpegFrame frame, IRawJpegData jpegData);
 
+        /// <summary>
+        /// Initializes this spectral decoder instance for decoding.
+        /// This should be called exactly once after all markers which can alter
+        /// spectral decoding parameters.
+        /// </summary>
+        public abstract void PrepareForDecoding();
+
         /// <summary>
         /// Converts single spectral jpeg stride to color stride in baseline
         /// decoding mode.

src/ImageSharp/Formats/Jpeg/Components/Decoder/SpectralConverter{TPixel}.cs

@@ -31,6 +31,10 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
         /// </summary>
         private readonly Configuration configuration;
 
+        private JpegFrame frame;
+
+        private IRawJpegData jpegData;
+
         /// <summary>
         /// Jpeg component converters from decompressed spectral to color data.
         /// </summary>
@@ -99,6 +103,8 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
         {
             if (!this.Converted)
             {
+                this.PrepareForDecoding();
+
                 int steps = (int)Math.Ceiling(this.pixelBuffer.Height / (float)this.pixelRowsPerStep);
 
                 for (int step = 0; step < steps; step++)
@@ -166,18 +172,27 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
         /// <inheritdoc/>
         public override void InjectFrameData(JpegFrame frame, IRawJpegData jpegData)
         {
+            this.frame = frame;
+            this.jpegData = jpegData;
+        }
+
+        /// <inheritdoc/>
+        public override void PrepareForDecoding()
+        {
+            DebugGuard.IsTrue(this.colorConverter == null, "SpectralConverter.PrepareForDecoding() must be called once.");
+
             MemoryAllocator allocator = this.configuration.MemoryAllocator;
 
             // color converter from RGB to TPixel
-            JpegColorConverterBase converter = this.GetColorConverter(frame, jpegData);
+            JpegColorConverterBase converter = this.GetColorConverter(this.frame, this.jpegData);
             this.colorConverter = converter;
 
             // resulting image size
-            Size pixelSize = CalculateResultingImageSize(frame.PixelSize, this.targetSize, out int blockPixelSize);
+            Size pixelSize = CalculateResultingImageSize(this.frame.PixelSize, this.targetSize, out int blockPixelSize);
 
             // iteration data
-            int majorBlockWidth = frame.Components.Max((component) => component.SizeInBlocks.Width);
-            int majorVerticalSamplingFactor = frame.Components.Max((component) => component.SamplingFactors.Height);
+            int majorBlockWidth = this.frame.Components.Max((component) => component.SizeInBlocks.Width);
+            int majorVerticalSamplingFactor = this.frame.Components.Max((component) => component.SamplingFactors.Height);
 
             this.pixelRowsPerStep = majorVerticalSamplingFactor * blockPixelSize;
 
@@ -193,7 +208,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
             int batchSize = converter.ElementsPerBatch;
             int batchRemainder = bufferWidth & (batchSize - 1);
             var postProcessorBufferSize = new Size(bufferWidth + (batchSize - batchRemainder), this.pixelRowsPerStep);
-            this.componentProcessors = this.CreateComponentProcessors(frame, jpegData, blockPixelSize, postProcessorBufferSize);
+            this.componentProcessors = this.CreateComponentProcessors(this.frame, this.jpegData, blockPixelSize, postProcessorBufferSize);
 
             // single 'stride' rgba32 buffer for conversion between spectral and TPixel
             this.rgbBuffer = allocator.Allocate<byte>(pixelSize.Width * 3);

src/ImageSharp/Formats/Jpeg/JpegDecoderCore.cs

@@ -198,6 +198,20 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
             where TPixel : unmanaged, IPixel<TPixel>
             => this.Decode<TPixel>(stream, targetSize: null, cancellationToken);
 
+        /// <inheritdoc/>
+        public IImageInfo Identify(BufferedReadStream stream, CancellationToken cancellationToken)
+        {
+            this.ParseStream(stream, spectralConverter: null, cancellationToken);
+            this.InitExifProfile();
+            this.InitIccProfile();
+            this.InitIptcProfile();
+            this.InitXmpProfile();
+            this.InitDerivedMetadataProperties();
+
+            Size pixelSize = this.Frame.PixelSize;
+            return new ImageInfo(new PixelTypeInfo(this.Frame.BitsPerPixel), pixelSize.Width, pixelSize.Height, this.Metadata);
+        }
+
         /// <summary>
         /// Decodes and downscales the image from the specified stream if possible.
         /// </summary>
@@ -205,10 +219,14 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
         /// <param name="stream">Stream.</param>
         /// <param name="targetSize">Target size.</param>
         /// <param name="cancellationToken">Cancellation token.</param>
-        public Image<TPixel> DecodeInto<TPixel>(BufferedReadStream stream, Size targetSize, CancellationToken cancellationToken)
+        internal Image<TPixel> DecodeInto<TPixel>(BufferedReadStream stream, Size targetSize, CancellationToken cancellationToken)
             where TPixel : unmanaged, IPixel<TPixel>
             => this.Decode<TPixel>(stream, targetSize, cancellationToken);
 
+        private Image<TPixel> Decode<TPixel>(BufferedReadStream stream, Size? targetSize, CancellationToken cancellationToken)
+            where TPixel : unmanaged, IPixel<TPixel>
+        {
+            using var spectralConverter = new SpectralConverter<TPixel>(this.Configuration, targetSize);
             this.ParseStream(stream, spectralConverter, cancellationToken);
             this.InitExifProfile();
             this.InitIccProfile();
@@ -222,20 +240,6 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
                 this.Metadata);
         }
 
-        /// <inheritdoc/>
-        public IImageInfo Identify(BufferedReadStream stream, CancellationToken cancellationToken)
-        {
-            this.ParseStream(stream, spectralConverter: null, cancellationToken);
-            this.InitExifProfile();
-            this.InitIccProfile();
-            this.InitIptcProfile();
-            this.InitXmpProfile();
-            this.InitDerivedMetadataProperties();
-
-            Size pixelSize = this.Frame.PixelSize;
-            return new ImageInfo(new PixelTypeInfo(this.Frame.BitsPerPixel), pixelSize.Width, pixelSize.Height, this.Metadata);
-        }
-
         /// <summary>
         /// Load quantization and/or Huffman tables for subsequent use for jpeg's embedded in tiff's,
         /// so those tables do not need to be duplicated with segmented tiff's (tiff's with multiple strips).
@@ -1263,6 +1267,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
             if (!metadataOnly)
             {
                 this.Frame.Init(maxH, maxV);
+                this.scanDecoder.InjectFrameData(this.Frame, this);
             }
         }
 

tests/ImageSharp.Benchmarks/Codecs/Jpeg/DecodeJpegParseStreamOnly.cs

@@ -57,6 +57,10 @@ namespace SixLabors.ImageSharp.Benchmarks.Codecs.Jpeg
             public override void InjectFrameData(JpegFrame frame, IRawJpegData jpegData)
             {
             }
+
+            public override void PrepareForDecoding()
+            {
+            }
         }
     }
 }

tests/ImageSharp.Tests/Formats/Jpg/SpectralJpegTests.cs

@@ -141,6 +141,8 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
         {
             private JpegFrame frame;
 
+            private IRawJpegData jpegData;
+
             private LibJpegTools.SpectralData spectralData;
 
             private int baselineScanRowCounter;
@@ -153,6 +155,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
                     // Progressive and multi-scan images must be loaded manually
                     if (this.frame.Progressive || this.frame.MultiScan)
                     {
+                        this.PrepareForDecoding();
                         LibJpegTools.ComponentData[] components = this.spectralData.Components;
                         for (int i = 0; i < components.Length; i++)
                         {
@@ -190,11 +193,15 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
             public override void InjectFrameData(JpegFrame frame, IRawJpegData jpegData)
             {
                 this.frame = frame;
+                this.jpegData = jpegData;
+            }
 
-                var spectralComponents = new LibJpegTools.ComponentData[frame.ComponentCount];
+            public override void PrepareForDecoding()
+            {
+                var spectralComponents = new LibJpegTools.ComponentData[this.frame.ComponentCount];
                 for (int i = 0; i < spectralComponents.Length; i++)
                 {
-                    var component = frame.Components[i] as JpegComponent;
+                    JpegComponent component = this.frame.Components[i];
                     spectralComponents[i] = new LibJpegTools.ComponentData(component.WidthInBlocks, component.HeightInBlocks, component.Index);
                 }