JpegDecoder: post-process baseline spectral data per MCU-row

src/ImageSharp/Common/Helpers/Numerics.cs

@@ -879,5 +879,13 @@ ref MemoryMarshal.GetReference(Log2DeBruijn),
                 (IntPtr)(int)((value * 0x07C4ACDDu) >> 27)); // uint|long -> IntPtr cast on 32-bit platforms does expensive overflow checks not needed here
         }
 #endif
+
+        /// <summary>
+        /// Fast division with ceiling for <see cref="uint"/> numbers.
+        /// </summary>
+        /// <param name="value">Divident value.</param>
+        /// <param name="divisor">Divisor value.</param>
+        /// <returns>Ceiled division result.</returns>
+        public static uint DivideCeil(uint value, uint divisor) => (value + divisor - 1) / divisor;
     }
 }

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

@@ -109,10 +109,10 @@ public void Dispose()
         public void Init()
         {
             this.WidthInBlocks = (int)MathF.Ceiling(
-                MathF.Ceiling(this.Frame.SamplesPerLine / 8F) * this.HorizontalSamplingFactor / this.Frame.MaxHorizontalFactor);
+                MathF.Ceiling(this.Frame.PixelWidth / 8F) * this.HorizontalSamplingFactor / this.Frame.MaxHorizontalFactor);
 
             this.HeightInBlocks = (int)MathF.Ceiling(
-                MathF.Ceiling(this.Frame.Scanlines / 8F) * this.VerticalSamplingFactor / this.Frame.MaxVerticalFactor);
+                MathF.Ceiling(this.Frame.PixelHeight / 8F) * this.VerticalSamplingFactor / this.Frame.MaxVerticalFactor);
 
             int blocksPerLineForMcu = this.Frame.McusPerLine * this.HorizontalSamplingFactor;
             int blocksPerColumnForMcu = this.Frame.McusPerColumn * this.VerticalSamplingFactor;
@@ -125,12 +125,20 @@ public void Init()
             {
                 JpegThrowHelper.ThrowBadSampling();
             }
+        }
+
+        public void AllocateSpectral(bool fullScan)
+        {
+            if (this.SpectralBlocks != null)
+            {
+                // this method will be called each scan marker so we need to allocate only once
+                return;
+            }
 
-            int totalNumberOfBlocks = blocksPerColumnForMcu * (blocksPerLineForMcu + 1);
-            int width = this.WidthInBlocks + 1;
-            int height = totalNumberOfBlocks / width;
+            int spectralAllocWidth = this.SizeInBlocks.Width;
+            int spectralAllocHeight = fullScan ? this.SizeInBlocks.Height : this.VerticalSamplingFactor;
 
-            this.SpectralBlocks = this.memoryAllocator.Allocate2D<Block8x8>(width, height, AllocationOptions.Clean);
+            this.SpectralBlocks = this.memoryAllocator.Allocate2D<Block8x8>(spectralAllocWidth, spectralAllocHeight, AllocationOptions.Clean);
         }
     }
 }

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

@@ -2,15 +2,12 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System;
-using System.Runtime.CompilerServices;
-using System.Runtime.InteropServices;
-
 using SixLabors.ImageSharp.Memory;
 
 namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
 {
     /// <summary>
-    /// Encapsulates postprocessing data for one component for <see cref="JpegImagePostProcessor"/>.
+    /// Encapsulates spectral data to rgba32 processing for one component.
     /// </summary>
     internal class JpegComponentPostProcessor : IDisposable
     {
@@ -27,23 +24,20 @@ internal class JpegComponentPostProcessor : IDisposable
         /// <summary>
         /// Initializes a new instance of the <see cref="JpegComponentPostProcessor"/> class.
         /// </summary>
-        public JpegComponentPostProcessor(MemoryAllocator memoryAllocator, JpegImagePostProcessor imagePostProcessor, IJpegComponent component)
+        public JpegComponentPostProcessor(MemoryAllocator memoryAllocator, IRawJpegData rawJpeg, Size postProcessorBufferSize, IJpegComponent component)
         {
             this.Component = component;
-            this.ImagePostProcessor = imagePostProcessor;
+            this.RawJpeg = rawJpeg;
             this.blockAreaSize = this.Component.SubSamplingDivisors * 8;
             this.ColorBuffer = memoryAllocator.Allocate2DOveraligned<float>(
-                imagePostProcessor.PostProcessorBufferSize.Width,
-                imagePostProcessor.PostProcessorBufferSize.Height,
+                postProcessorBufferSize.Width,
+                postProcessorBufferSize.Height,
                 this.blockAreaSize.Height);
 
-            this.BlockRowsPerStep = JpegImagePostProcessor.BlockRowsPerStep / this.Component.SubSamplingDivisors.Height;
+            this.BlockRowsPerStep = postProcessorBufferSize.Height / 8 / this.Component.SubSamplingDivisors.Height;
         }
 
-        /// <summary>
-        /// Gets the <see cref="JpegImagePostProcessor"/>
-        /// </summary>
-        public JpegImagePostProcessor ImagePostProcessor { get; }
+        public IRawJpegData RawJpeg { get; }
 
         /// <summary>
         /// Gets the <see cref="Component"/>
@@ -66,37 +60,38 @@ public JpegComponentPostProcessor(MemoryAllocator memoryAllocator, JpegImagePost
         public int BlockRowsPerStep { get; }
 
         /// <inheritdoc />
-        public void Dispose()
-        {
-            this.ColorBuffer.Dispose();
-        }
+        public void Dispose() => this.ColorBuffer.Dispose();
 
         /// <summary>
         /// Invoke <see cref="JpegBlockPostProcessor"/> for <see cref="BlockRowsPerStep"/> block rows, copy the result into <see cref="ColorBuffer"/>.
         /// </summary>
-        public void CopyBlocksToColorBuffer()
+        public void CopyBlocksToColorBuffer(int step)
         {
-            var blockPp = new JpegBlockPostProcessor(this.ImagePostProcessor.RawJpeg, this.Component);
-            float maximumValue = MathF.Pow(2, this.ImagePostProcessor.RawJpeg.Precision) - 1;
+            Buffer2D<Block8x8> spectralBuffer = this.Component.SpectralBlocks;
+
+            var blockPp = new JpegBlockPostProcessor(this.RawJpeg, this.Component);
+            float maximumValue = MathF.Pow(2, this.RawJpeg.Precision) - 1;
 
             int destAreaStride = this.ColorBuffer.Width;
 
+            int yBlockStart = step * this.BlockRowsPerStep;
+
             for (int y = 0; y < this.BlockRowsPerStep; y++)
             {
-                int yBlock = this.currentComponentRowInBlocks + y;
+                int yBlock = yBlockStart + y;
 
-                if (yBlock >= this.SizeInBlocks.Height)
+                if (yBlock >= spectralBuffer.Height)
                 {
                     break;
                 }
 
                 int yBuffer = y * this.blockAreaSize.Height;
 
                 Span<float> colorBufferRow = this.ColorBuffer.GetRowSpan(yBuffer);
-                Span<Block8x8> blockRow = this.Component.SpectralBlocks.GetRowSpan(yBlock);
+                Span<Block8x8> blockRow = spectralBuffer.GetRowSpan(yBlock);
 
                 // see: https://github.com/SixLabors/ImageSharp/issues/824
-                int widthInBlocks = Math.Min(this.Component.SpectralBlocks.Width, this.SizeInBlocks.Width);
+                int widthInBlocks = Math.Min(spectralBuffer.Width, this.SizeInBlocks.Width);
 
                 for (int xBlock = 0; xBlock < widthInBlocks; xBlock++)
                 {
@@ -107,7 +102,20 @@ public void CopyBlocksToColorBuffer()
                     blockPp.ProcessBlockColorsInto(ref block, ref destAreaOrigin, destAreaStride, maximumValue);
                 }
             }
+        }
+
+        public void ClearSpectralBuffers()
+        {
+            Buffer2D<Block8x8> spectralBlocks = this.Component.SpectralBlocks;
+            for (int i = 0; i < spectralBlocks.Height; i++)
+            {
+                spectralBlocks.GetRowSpan(i).Clear();
+            }
+        }
 
+        public void CopyBlocksToColorBuffer()
+        {
+            this.CopyBlocksToColorBuffer(this.currentComponentRowInBlocks);
             this.currentComponentRowInBlocks += this.BlockRowsPerStep;
         }
     }

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

@@ -20,6 +20,14 @@ internal sealed class JpegFrame : IDisposable
         /// </summary>
         public bool Progressive { get; set; }
 
+        /// <summary>
+        /// Gets or sets a value indicating whether the frame is encoded using multiple scans (SOS markers).
+        /// </summary>
+        /// <remarks>
+        /// This is true for progressive and baseline non-interleaved images.
+        /// </remarks>
+        public bool MultiScan { get; set; }
+
         /// <summary>
         /// Gets or sets the precision.
         /// </summary>
@@ -28,12 +36,12 @@ internal sealed class JpegFrame : IDisposable
         /// <summary>
         /// Gets or sets the number of scanlines within the frame.
         /// </summary>
-        public int Scanlines { get; set; }
+        public int PixelHeight { get; set; }
 
         /// <summary>
         /// Gets or sets the number of samples per scanline.
         /// </summary>
-        public int SamplesPerLine { get; set; }
+        public int PixelWidth { get; set; }
 
         /// <summary>
         /// Gets or sets the number of components within a frame. In progressive frames this value can range from only 1 to 4.
@@ -95,14 +103,23 @@ public void Dispose()
         /// </summary>
         public void InitComponents()
         {
-            this.McusPerLine = (int)MathF.Ceiling(this.SamplesPerLine / 8F / this.MaxHorizontalFactor);
-            this.McusPerColumn = (int)MathF.Ceiling(this.Scanlines / 8F / this.MaxVerticalFactor);
+            this.McusPerLine = (int)Numerics.DivideCeil((uint)this.PixelWidth, (uint)this.MaxHorizontalFactor * 8);
+            this.McusPerColumn = (int)Numerics.DivideCeil((uint)this.PixelHeight, (uint)this.MaxVerticalFactor * 8);
 
             for (int i = 0; i < this.ComponentCount; i++)
             {
                 JpegComponent component = this.Components[i];
                 component.Init();
             }
         }
+
+        public void AllocateComponents(bool fullScan)
+        {
+            for (int i = 0; i < this.ComponentCount; i++)
+            {
+                JpegComponent component = this.Components[i];
+                component.AllocateSpectral(fullScan);
+            }
+        }
     }
 }