Working version per-row

src/ImageSharp/Processing/Processors/Convolution/Convolution2DProcessor{TPixel}.cs

@@ -66,12 +66,17 @@ namespace SixLabors.ImageSharp.Processing.Processors.Convolution
             source.CopyTo(targetPixels);
 
             var interest = Rectangle.Intersect(this.SourceRectangle, source.Bounds());
+
+            // We use a rectangle 3x the interest width to allocate a buffer big enough
+            // for source and target bulk pixel conversion.
+            var operationBounds = new Rectangle(interest.X, interest.Y, interest.Width * 3, interest.Height);
+
             using (var map = new KernelSamplingMap(allocator))
             {
                 // Since the kernel sizes are identical we can use a single map.
                 map.BuildSamplingOffsetMap(this.KernelY, interest);
 
-                var operation = new RowOperation(
+                var operation = new Convolution2DRowOperation<TPixel>(
                     interest,
                     targetPixels,
                     source.PixelBuffer,
@@ -81,9 +86,9 @@ namespace SixLabors.ImageSharp.Processing.Processors.Convolution
                     this.Configuration,
                     this.PreserveAlpha);
 
-                ParallelRowIterator.IterateRows<RowOperation, Vector4>(
+                ParallelRowIterator.IterateRows<Convolution2DRowOperation<TPixel>, Vector4>(
                     this.Configuration,
-                    interest,
+                    operationBounds,
                     in operation);
             }
 

src/ImageSharp/Processing/Processors/Convolution/Convolution2DRowOperation{TPixel}.cs

@@ -0,0 +1,193 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+using System.Numerics;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using SixLabors.ImageSharp.Advanced;
+using SixLabors.ImageSharp.Memory;
+using SixLabors.ImageSharp.PixelFormats;
+
+namespace SixLabors.ImageSharp.Processing.Processors.Convolution
+{
+    /// <summary>
+    /// A <see langword="struct"/> implementing the logic for 2D convolution.
+    /// </summary>
+    internal readonly struct Convolution2DRowOperation<TPixel> : IRowOperation<Vector4>
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        private readonly Rectangle bounds;
+        private readonly Buffer2D<TPixel> targetPixels;
+        private readonly Buffer2D<TPixel> sourcePixels;
+        private readonly KernelSamplingMap map;
+        private readonly DenseMatrix<float> kernelMatrixY;
+        private readonly DenseMatrix<float> kernelMatrixX;
+        private readonly Configuration configuration;
+        private readonly bool preserveAlpha;
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public Convolution2DRowOperation(
+            Rectangle bounds,
+            Buffer2D<TPixel> targetPixels,
+            Buffer2D<TPixel> sourcePixels,
+            KernelSamplingMap map,
+            DenseMatrix<float> kernelMatrixY,
+            DenseMatrix<float> kernelMatrixX,
+            Configuration configuration,
+            bool preserveAlpha)
+        {
+            this.bounds = bounds;
+            this.targetPixels = targetPixels;
+            this.sourcePixels = sourcePixels;
+            this.map = map;
+            this.kernelMatrixY = kernelMatrixY;
+            this.kernelMatrixX = kernelMatrixX;
+            this.configuration = configuration;
+            this.preserveAlpha = preserveAlpha;
+        }
+
+        /// <inheritdoc/>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public void Invoke(int y, Span<Vector4> span)
+        {
+            if (this.preserveAlpha)
+            {
+                this.Convolve3(y, span);
+            }
+            else
+            {
+                this.Convolve4(y, span);
+            }
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private void Convolve3(int y, Span<Vector4> span)
+        {
+            // Span is 3x bounds.
+            int boundsX = this.bounds.X;
+            int boundsWidth = this.bounds.Width;
+            Span<Vector4> sourceBuffer = span.Slice(0, boundsWidth);
+            Span<Vector4> targetYBuffer = span.Slice(boundsWidth, boundsWidth);
+            Span<Vector4> targetXBuffer = span.Slice(boundsWidth * 2, boundsWidth);
+
+            var state = new Convolution2DState(in this.kernelMatrixY, in this.kernelMatrixX, this.map);
+            ReadOnlyKernel kernelY = state.KernelY;
+            ReadOnlyKernel kernelX = state.KernelX;
+            int row = y - this.bounds.Y;
+            ref int sampleRowBase = ref state.GetSampleRow(row);
+
+            // Clear the target buffers for each row run.
+            targetYBuffer.Clear();
+            targetXBuffer.Clear();
+            ref Vector4 targetBaseY = ref MemoryMarshal.GetReference(targetYBuffer);
+            ref Vector4 targetBaseX = ref MemoryMarshal.GetReference(targetXBuffer);
+
+            Span<TPixel> sourceRow;
+            for (int kY = 0; kY < kernelY.Rows; kY++)
+            {
+                // Get the precalculated source sample row for this kernel row and copy to our buffer.
+                int offsetY = Unsafe.Add(ref sampleRowBase, kY);
+                sourceRow = this.sourcePixels.GetRowSpan(offsetY).Slice(boundsX, boundsWidth);
+                PixelOperations<TPixel>.Instance.ToVector4(this.configuration, sourceRow, sourceBuffer);
+
+                ref Vector4 sourceBase = ref MemoryMarshal.GetReference(sourceBuffer);
+
+                for (int x = 0; x < sourceBuffer.Length; x++)
+                {
+                    ref int sampleColumnBase = ref state.GetSampleColumn(x);
+                    ref Vector4 targetY = ref Unsafe.Add(ref targetBaseY, x);
+                    ref Vector4 targetX = ref Unsafe.Add(ref targetBaseX, x);
+
+                    for (int kX = 0; kX < kernelY.Columns; kX++)
+                    {
+                        int offsetX = Unsafe.Add(ref sampleColumnBase, kX) - boundsX;
+                        Vector4 sample = Unsafe.Add(ref sourceBase, offsetX);
+                        targetY += kernelX[kY, kX] * sample;
+                        targetX += kernelY[kY, kX] * sample;
+                    }
+                }
+            }
+
+            // Now we need to combine the values and copy the original alpha values from the source row.
+            sourceRow = this.sourcePixels.GetRowSpan(y).Slice(boundsX, boundsWidth);
+            PixelOperations<TPixel>.Instance.ToVector4(this.configuration, sourceRow, sourceBuffer);
+
+            for (int x = 0; x < sourceRow.Length; x++)
+            {
+                ref Vector4 target = ref Unsafe.Add(ref targetBaseY, x);
+                Vector4 vectorY = target;
+                Vector4 vectorX = Unsafe.Add(ref targetBaseX, x);
+
+                target = Vector4.SquareRoot((vectorX * vectorX) + (vectorY * vectorY));
+                target.W = Unsafe.Add(ref MemoryMarshal.GetReference(sourceBuffer), x).W;
+            }
+
+            Span<TPixel> targetRowSpan = this.targetPixels.GetRowSpan(y).Slice(boundsX, boundsWidth);
+            PixelOperations<TPixel>.Instance.FromVector4Destructive(this.configuration, targetYBuffer, targetRowSpan);
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private void Convolve4(int y, Span<Vector4> span)
+        {
+            // Span is 2x bounds.
+            int boundsX = this.bounds.X;
+            int boundsWidth = this.bounds.Width;
+            Span<Vector4> sourceBuffer = span.Slice(0, boundsWidth);
+            Span<Vector4> targetYBuffer = span.Slice(boundsWidth, boundsWidth);
+            Span<Vector4> targetXBuffer = span.Slice(boundsWidth * 2, boundsWidth);
+
+            var state = new Convolution2DState(in this.kernelMatrixY, in this.kernelMatrixX, this.map);
+            ReadOnlyKernel kernelY = state.KernelY;
+            ReadOnlyKernel kernelX = state.KernelX;
+            int row = y - this.bounds.Y;
+            ref int sampleRowBase = ref state.GetSampleRow(row);
+
+            // Clear the target buffers for each row run.
+            targetYBuffer.Clear();
+            targetXBuffer.Clear();
+            ref Vector4 targetBaseY = ref MemoryMarshal.GetReference(targetYBuffer);
+            ref Vector4 targetBaseX = ref MemoryMarshal.GetReference(targetXBuffer);
+
+            for (int kY = 0; kY < kernelY.Rows; kY++)
+            {
+                // Get the precalculated source sample row for this kernel row and copy to our buffer.
+                int offsetY = Unsafe.Add(ref sampleRowBase, kY);
+                Span<TPixel> sourceRow = this.sourcePixels.GetRowSpan(offsetY).Slice(boundsX, boundsWidth);
+                PixelOperations<TPixel>.Instance.ToVector4(this.configuration, sourceRow, sourceBuffer);
+
+                Numerics.Premultiply(sourceBuffer);
+                ref Vector4 sourceBase = ref MemoryMarshal.GetReference(sourceBuffer);
+
+                for (int x = 0; x < sourceBuffer.Length; x++)
+                {
+                    ref int sampleColumnBase = ref state.GetSampleColumn(x);
+                    ref Vector4 targetY = ref Unsafe.Add(ref targetBaseY, x);
+                    ref Vector4 targetX = ref Unsafe.Add(ref targetBaseX, x);
+
+                    for (int kX = 0; kX < kernelY.Columns; kX++)
+                    {
+                        int offsetX = Unsafe.Add(ref sampleColumnBase, kX) - boundsX;
+                        Vector4 sample = Unsafe.Add(ref sourceBase, offsetX);
+                        targetY += kernelX[kY, kX] * sample;
+                        targetX += kernelY[kY, kX] * sample;
+                    }
+                }
+            }
+
+            for (int x = 0; x < targetYBuffer.Length; x++)
+            {
+                ref Vector4 target = ref Unsafe.Add(ref targetBaseY, x);
+                Vector4 vectorY = target;
+                Vector4 vectorX = Unsafe.Add(ref targetBaseX, x);
+
+                target = Vector4.SquareRoot((vectorX * vectorX) + (vectorY * vectorY));
+            }
+
+            Numerics.UnPremultiply(targetYBuffer);
+
+            Span<TPixel> targetRow = this.targetPixels.GetRowSpan(y).Slice(boundsX, boundsWidth);
+            PixelOperations<TPixel>.Instance.FromVector4Destructive(this.configuration, targetYBuffer, targetRow);
+        }
+    }
+}

src/ImageSharp/Processing/Processors/Convolution/Convolution2DState.cs

@@ -44,11 +44,11 @@ namespace SixLabors.ImageSharp.Processing.Processors.Convolution
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public readonly ref int GetSampleOffsetRow(int row)
+        public readonly ref int GetSampleRow(int row)
             => ref Unsafe.Add(ref MemoryMarshal.GetReference(this.rowOffsetMap), row * this.kernelHeight);
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public readonly ref int GetSampleOffsetColumn(int column)
+        public readonly ref int GetSampleColumn(int column)
             => ref Unsafe.Add(ref MemoryMarshal.GetReference(this.columnOffsetMap), column * this.kernelWidth);
     }
 }

src/ImageSharp/Processing/Processors/Convolution/Convolution2PassProcessor{TPixel}.cs

@@ -63,12 +63,16 @@ namespace SixLabors.ImageSharp.Processing.Processors.Convolution
 
             var interest = Rectangle.Intersect(this.SourceRectangle, source.Bounds());
 
+            // We use a rectangle 2x the interest width to allocate a buffer big enough
+            // for source and target bulk pixel conversion.
+            var operationBounds = new Rectangle(interest.X, interest.Y, interest.Width * 2, interest.Height);
+
             using (var mapX = new KernelSamplingMap(this.Configuration.MemoryAllocator))
             {
                 mapX.BuildSamplingOffsetMap(this.KernelX, interest);
 
                 // Horizontal convolution
-                var horizontalOperation = new RowOperation(
+                var horizontalOperation = new ConvolutionRowOperation<TPixel>(
                     interest,
                     firstPassPixels,
                     source.PixelBuffer,
@@ -77,9 +81,9 @@ namespace SixLabors.ImageSharp.Processing.Processors.Convolution
                     this.Configuration,
                     this.PreserveAlpha);
 
-                ParallelRowIterator.IterateRows<RowOperation, Vector4>(
+                ParallelRowIterator.IterateRows<ConvolutionRowOperation<TPixel>, Vector4>(
                     this.Configuration,
-                    interest,
+                    operationBounds,
                     in horizontalOperation);
             }
 
@@ -88,7 +92,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Convolution
                 mapY.BuildSamplingOffsetMap(this.KernelY, interest);
 
                 // Vertical convolution
-                var verticalOperation = new RowOperation(
+                var verticalOperation = new ConvolutionRowOperation<TPixel>(
                     interest,
                     source.PixelBuffer,
                     firstPassPixels,
@@ -97,83 +101,11 @@ namespace SixLabors.ImageSharp.Processing.Processors.Convolution
                     this.Configuration,
                     this.PreserveAlpha);
 
-                ParallelRowIterator.IterateRows<RowOperation, Vector4>(
+                ParallelRowIterator.IterateRows<ConvolutionRowOperation<TPixel>, Vector4>(
                     this.Configuration,
-                    interest,
+                    operationBounds,
                     in verticalOperation);
             }
         }
-
-        /// <summary>
-        /// A <see langword="struct"/> implementing the convolution logic for <see cref="Convolution2PassProcessor{T}"/>.
-        /// </summary>
-        private readonly struct RowOperation : IRowOperation<Vector4>
-        {
-            private readonly Rectangle bounds;
-            private readonly Buffer2D<TPixel> targetPixels;
-            private readonly Buffer2D<TPixel> sourcePixels;
-            private readonly KernelSamplingMap map;
-            private readonly DenseMatrix<float> kernel;
-            private readonly Configuration configuration;
-            private readonly bool preserveAlpha;
-
-            [MethodImpl(InliningOptions.ShortMethod)]
-            public RowOperation(
-                Rectangle bounds,
-                Buffer2D<TPixel> targetPixels,
-                Buffer2D<TPixel> sourcePixels,
-                KernelSamplingMap map,
-                DenseMatrix<float> kernel,
-                Configuration configuration,
-                bool preserveAlpha)
-            {
-                this.bounds = bounds;
-                this.targetPixels = targetPixels;
-                this.sourcePixels = sourcePixels;
-                this.map = map;
-                this.kernel = kernel;
-                this.configuration = configuration;
-                this.preserveAlpha = preserveAlpha;
-            }
-
-            /// <inheritdoc/>
-            [MethodImpl(InliningOptions.ShortMethod)]
-            public void Invoke(int y, Span<Vector4> span)
-            {
-                ref Vector4 targetRowRef = ref MemoryMarshal.GetReference(span);
-                Span<TPixel> targetRowSpan = this.targetPixels.GetRowSpan(y).Slice(this.bounds.X);
-                PixelOperations<TPixel>.Instance.ToVector4(this.configuration, targetRowSpan.Slice(0, span.Length), span);
-
-                var state = new ConvolutionState(in this.kernel, this.map);
-                int row = y - this.bounds.Y;
-
-                if (this.preserveAlpha)
-                {
-                    for (int column = 0; column < this.bounds.Width; column++)
-                    {
-                        Convolver.Convolve3(
-                            in state,
-                            this.sourcePixels,
-                            ref targetRowRef,
-                            row,
-                            column);
-                    }
-                }
-                else
-                {
-                    for (int column = 0; column < this.bounds.Width; column++)
-                    {
-                        Convolver.Convolve4(
-                            in state,
-                            this.sourcePixels,
-                            ref targetRowRef,
-                            row,
-                            column);
-                    }
-                }
-
-                PixelOperations<TPixel>.Instance.FromVector4Destructive(this.configuration, span, targetRowSpan);
-            }
-        }
     }
 }

src/ImageSharp/Processing/Processors/Convolution/ConvolutionProcessor{TPixel}.cs

@@ -57,6 +57,10 @@ namespace SixLabors.ImageSharp.Processing.Processors.Convolution
             source.CopyTo(targetPixels);
 
             var interest = Rectangle.Intersect(this.SourceRectangle, source.Bounds());
+
+            // We use a rectangle 2x the interest width to allocate a buffer big enough
+            // for source and target bulk pixel conversion.
+            var operationBounds = new Rectangle(interest.X, interest.Y, interest.Width * 2, interest.Height);
             using (var map = new KernelSamplingMap(allocator))
             {
                 map.BuildSamplingOffsetMap(this.KernelXY, interest);
@@ -64,7 +68,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Convolution
                 var operation = new RowOperation(interest, targetPixels, source.PixelBuffer, map, this.KernelXY, this.Configuration, this.PreserveAlpha);
                 ParallelRowIterator.IterateRows<RowOperation, Vector4>(
                    this.Configuration,
-                   interest,
+                   operationBounds,
                    in operation);
             }
 
@@ -107,39 +111,93 @@ namespace SixLabors.ImageSharp.Processing.Processors.Convolution
             [MethodImpl(InliningOptions.ShortMethod)]
             public void Invoke(int y, Span<Vector4> span)
             {
+                // Span is 2x bounds.
+                int boundsX = this.bounds.X;
+                int boundsWidth = this.bounds.Width;
+                Span<Vector4> sourceBuffer = span.Slice(0, this.bounds.Width);
+                Span<Vector4> targetBuffer = span.Slice(this.bounds.Width);
+
                 ref Vector4 targetRowRef = ref MemoryMarshal.GetReference(span);
-                Span<TPixel> targetRowSpan = this.targetPixels.GetRowSpan(y).Slice(this.bounds.X);
+                Span<TPixel> targetRowSpan = this.targetPixels.GetRowSpan(y).Slice(boundsX, boundsWidth);
-                PixelOperations<TPixel>.Instance.ToVector4(this.configuration, targetRowSpan.Slice(0, span.Length), span);
 
                 var state = new ConvolutionState(in this.kernel, this.map);
                 int row = y - this.bounds.Y;
+                ref int sampleRowBase = ref state.GetSampleRow(row);
 
                 if (this.preserveAlpha)
                 {
-                    for (int column = 0; column < this.bounds.Width; column++)
+                    // Clear the target buffer for each row run.
+                    targetBuffer.Clear();
+                    ref Vector4 targetBase = ref MemoryMarshal.GetReference(targetBuffer);
+
+                    Span<TPixel> sourceRow;
+                    for (int kY = 0; kY < state.Kernel.Rows; kY++)
                     {
-                        Convolver.Convolve3(
+                        // Get the precalculated source sample row for this kernel row and copy to our buffer.
-                            in state,
+                        int offsetY = Unsafe.Add(ref sampleRowBase, kY);
-                            this.sourcePixels,
+                        sourceRow = this.sourcePixels.GetRowSpan(offsetY).Slice(boundsX, boundsWidth);
-                            ref targetRowRef,
+                        PixelOperations<TPixel>.Instance.ToVector4(this.configuration, sourceRow, sourceBuffer);
-                            row,
+
-                            column);
+                        ref Vector4 sourceBase = ref MemoryMarshal.GetReference(sourceBuffer);
+
+                        for (int x = 0; x < sourceBuffer.Length; x++)
+                        {
+                            ref int sampleColumnBase = ref state.GetSampleColumn(x);
+                            ref Vector4 target = ref Unsafe.Add(ref targetBase, x);
+
+                            for (int kX = 0; kX < state.Kernel.Columns; kX++)
+                            {
+                                int offsetX = Unsafe.Add(ref sampleColumnBase, kX) - boundsX;
+                                Vector4 sample = Unsafe.Add(ref sourceBase, offsetX);
+                                target += state.Kernel[kY, kX] * sample;
+                            }
+                        }
+                    }
+
+                    // Now we need to copy the original alpha values from the source row.
+                    sourceRow = this.sourcePixels.GetRowSpan(y).Slice(boundsX, boundsWidth);
+                    PixelOperations<TPixel>.Instance.ToVector4(this.configuration, sourceRow, sourceBuffer);
+
+                    for (int x = 0; x < sourceRow.Length; x++)
+                    {
+                        ref Vector4 target = ref Unsafe.Add(ref targetBase, x);
+                        target.W = Unsafe.Add(ref MemoryMarshal.GetReference(sourceBuffer), x).W;
                     }
                 }
                 else
                 {
-                    for (int column = 0; column < this.bounds.Width; column++)
+                    // Clear the target buffer for each row run.
+                    targetBuffer.Clear();
+                    ref Vector4 targetBase = ref MemoryMarshal.GetReference(targetBuffer);
+
+                    for (int kY = 0; kY < state.Kernel.Rows; kY++)
                     {
-                        Convolver.Convolve4(
+                        // Get the precalculated source sample row for this kernel row and copy to our buffer.
-                            in state,
+                        int offsetY = Unsafe.Add(ref sampleRowBase, kY);
-                            this.sourcePixels,
+                        Span<TPixel> sourceRow = this.sourcePixels.GetRowSpan(offsetY).Slice(boundsX, boundsWidth);
-                            ref targetRowRef,
+                        PixelOperations<TPixel>.Instance.ToVector4(this.configuration, sourceRow, sourceBuffer);
-                            row,
+
-                            column);
+                        Numerics.Premultiply(sourceBuffer);
+                        ref Vector4 sourceBase = ref MemoryMarshal.GetReference(sourceBuffer);
+
+                        for (int x = 0; x < sourceBuffer.Length; x++)
+                        {
+                            ref int sampleColumnBase = ref state.GetSampleColumn(x);
+                            ref Vector4 target = ref Unsafe.Add(ref targetBase, x);
+
+                            for (int kX = 0; kX < state.Kernel.Columns; kX++)
+                            {
+                                int offsetX = Unsafe.Add(ref sampleColumnBase, kX) - boundsX;
+                                Vector4 sample = Unsafe.Add(ref sourceBase, offsetX);
+                                target += state.Kernel[kY, kX] * sample;
+                            }
+                        }
                     }
+
+                    Numerics.UnPremultiply(targetBuffer);
                 }
 
-                PixelOperations<TPixel>.Instance.FromVector4Destructive(this.configuration, span, targetRowSpan);
+                PixelOperations<TPixel>.Instance.FromVector4Destructive(this.configuration, targetBuffer, targetRowSpan);
             }
         }
     }

src/ImageSharp/Processing/Processors/Convolution/ConvolutionRowOperation{TPixel}.cs

@@ -0,0 +1,169 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+using System.Numerics;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using SixLabors.ImageSharp.Advanced;
+using SixLabors.ImageSharp.Memory;
+using SixLabors.ImageSharp.PixelFormats;
+
+namespace SixLabors.ImageSharp.Processing.Processors.Convolution
+{
+    /// <summary>
+    /// A <see langword="struct"/> implementing the logic for 1D convolution.
+    /// </summary>
+    internal readonly struct ConvolutionRowOperation<TPixel> : IRowOperation<Vector4>
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        private readonly Rectangle bounds;
+        private readonly Buffer2D<TPixel> targetPixels;
+        private readonly Buffer2D<TPixel> sourcePixels;
+        private readonly KernelSamplingMap map;
+        private readonly DenseMatrix<float> kernelMatrix;
+        private readonly Configuration configuration;
+        private readonly bool preserveAlpha;
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public ConvolutionRowOperation(
+            Rectangle bounds,
+            Buffer2D<TPixel> targetPixels,
+            Buffer2D<TPixel> sourcePixels,
+            KernelSamplingMap map,
+            DenseMatrix<float> kernelMatrix,
+            Configuration configuration,
+            bool preserveAlpha)
+        {
+            this.bounds = bounds;
+            this.targetPixels = targetPixels;
+            this.sourcePixels = sourcePixels;
+            this.map = map;
+            this.kernelMatrix = kernelMatrix;
+            this.configuration = configuration;
+            this.preserveAlpha = preserveAlpha;
+        }
+
+        /// <inheritdoc/>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public void Invoke(int y, Span<Vector4> span)
+        {
+            if (this.preserveAlpha)
+            {
+                this.Convolve3(y, span);
+            }
+            else
+            {
+                this.Convolve4(y, span);
+            }
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private void Convolve3(int y, Span<Vector4> span)
+        {
+            // Span is 2x bounds.
+            int boundsX = this.bounds.X;
+            int boundsWidth = this.bounds.Width;
+            Span<Vector4> sourceBuffer = span.Slice(0, this.bounds.Width);
+            Span<Vector4> targetBuffer = span.Slice(this.bounds.Width);
+
+            ref Vector4 targetRowRef = ref MemoryMarshal.GetReference(span);
+            Span<TPixel> targetRowSpan = this.targetPixels.GetRowSpan(y).Slice(boundsX, boundsWidth);
+
+            var state = new ConvolutionState(in this.kernelMatrix, this.map);
+            ReadOnlyKernel kernel = state.Kernel;
+            int row = y - this.bounds.Y;
+            ref int sampleRowBase = ref state.GetSampleRow(row);
+
+            // Clear the target buffer for each row run.
+            targetBuffer.Clear();
+            ref Vector4 targetBase = ref MemoryMarshal.GetReference(targetBuffer);
+
+            Span<TPixel> sourceRow;
+            for (int kY = 0; kY < kernel.Rows; kY++)
+            {
+                // Get the precalculated source sample row for this kernel row and copy to our buffer.
+                int offsetY = Unsafe.Add(ref sampleRowBase, kY);
+                sourceRow = this.sourcePixels.GetRowSpan(offsetY).Slice(boundsX, boundsWidth);
+                PixelOperations<TPixel>.Instance.ToVector4(this.configuration, sourceRow, sourceBuffer);
+
+                ref Vector4 sourceBase = ref MemoryMarshal.GetReference(sourceBuffer);
+
+                for (int x = 0; x < sourceBuffer.Length; x++)
+                {
+                    ref int sampleColumnBase = ref state.GetSampleColumn(x);
+                    ref Vector4 target = ref Unsafe.Add(ref targetBase, x);
+
+                    for (int kX = 0; kX < kernel.Columns; kX++)
+                    {
+                        int offsetX = Unsafe.Add(ref sampleColumnBase, kX) - boundsX;
+                        Vector4 sample = Unsafe.Add(ref sourceBase, offsetX);
+                        target += kernel[kY, kX] * sample;
+                    }
+                }
+            }
+
+            // Now we need to copy the original alpha values from the source row.
+            sourceRow = this.sourcePixels.GetRowSpan(y).Slice(boundsX, boundsWidth);
+            PixelOperations<TPixel>.Instance.ToVector4(this.configuration, sourceRow, sourceBuffer);
+
+            for (int x = 0; x < sourceRow.Length; x++)
+            {
+                ref Vector4 target = ref Unsafe.Add(ref targetBase, x);
+                target.W = Unsafe.Add(ref MemoryMarshal.GetReference(sourceBuffer), x).W;
+            }
+
+            PixelOperations<TPixel>.Instance.FromVector4Destructive(this.configuration, targetBuffer, targetRowSpan);
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private void Convolve4(int y, Span<Vector4> span)
+        {
+            // Span is 2x bounds.
+            int boundsX = this.bounds.X;
+            int boundsWidth = this.bounds.Width;
+            Span<Vector4> sourceBuffer = span.Slice(0, this.bounds.Width);
+            Span<Vector4> targetBuffer = span.Slice(this.bounds.Width);
+
+            ref Vector4 targetRowRef = ref MemoryMarshal.GetReference(span);
+            Span<TPixel> targetRowSpan = this.targetPixels.GetRowSpan(y).Slice(boundsX, boundsWidth);
+
+            var state = new ConvolutionState(in this.kernelMatrix, this.map);
+            ReadOnlyKernel kernel = state.Kernel;
+            int row = y - this.bounds.Y;
+            ref int sampleRowBase = ref state.GetSampleRow(row);
+
+            // Clear the target buffer for each row run.
+            targetBuffer.Clear();
+            ref Vector4 targetBase = ref MemoryMarshal.GetReference(targetBuffer);
+
+            for (int kY = 0; kY < kernel.Rows; kY++)
+            {
+                // Get the precalculated source sample row for this kernel row and copy to our buffer.
+                int offsetY = Unsafe.Add(ref sampleRowBase, kY);
+                Span<TPixel> sourceRow = this.sourcePixels.GetRowSpan(offsetY).Slice(boundsX, boundsWidth);
+                PixelOperations<TPixel>.Instance.ToVector4(this.configuration, sourceRow, sourceBuffer);
+
+                Numerics.Premultiply(sourceBuffer);
+                ref Vector4 sourceBase = ref MemoryMarshal.GetReference(sourceBuffer);
+
+                for (int x = 0; x < sourceBuffer.Length; x++)
+                {
+                    ref int sampleColumnBase = ref state.GetSampleColumn(x);
+                    ref Vector4 target = ref Unsafe.Add(ref targetBase, x);
+
+                    for (int kX = 0; kX < kernel.Columns; kX++)
+                    {
+                        int offsetX = Unsafe.Add(ref sampleColumnBase, kX) - boundsX;
+                        Vector4 sample = Unsafe.Add(ref sourceBase, offsetX);
+                        target += kernel[kY, kX] * sample;
+                    }
+                }
+            }
+
+            Numerics.UnPremultiply(targetBuffer);
+
+            PixelOperations<TPixel>.Instance.FromVector4Destructive(this.configuration, targetBuffer, targetRowSpan);
+        }
+    }
+}

src/ImageSharp/Processing/Processors/Convolution/ConvolutionState.cs

@@ -35,11 +35,11 @@ namespace SixLabors.ImageSharp.Processing.Processors.Convolution
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public readonly ref int GetSampleOffsetRow(int row)
+        public readonly ref int GetSampleRow(int row)
             => ref Unsafe.Add(ref MemoryMarshal.GetReference(this.rowOffsetMap), row * this.kernelHeight);
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public readonly ref int GetSampleOffsetColumn(int column)
+        public readonly ref int GetSampleColumn(int column)
             => ref Unsafe.Add(ref MemoryMarshal.GetReference(this.columnOffsetMap), column * this.kernelWidth);
     }
 }

src/ImageSharp/Processing/Processors/Convolution/Convolver.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
+using System;
 using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
@@ -100,12 +101,12 @@ namespace SixLabors.ImageSharp
             Vector4 vectorY = default;
             Vector4 vectorX = default;
 
-            ref int sampleOffsetRowBase = ref state.GetSampleOffsetRow(row);
+            ref int sampleOffsetRowBase = ref state.GetSampleRow(row);
             for (int y = 0; y < kernelHeight; y++)
             {
                 int offsetY = Unsafe.Add(ref sampleOffsetRowBase, y);
                 ref TPixel sourceRowBase = ref MemoryMarshal.GetReference(sourcePixels.GetRowSpan(offsetY));
-                ref int sampleOffsetColumnBase = ref state.GetSampleOffsetColumn(column);
+                ref int sampleOffsetColumnBase = ref state.GetSampleColumn(column);
 
                 for (int x = 0; x < kernelWidth; x++)
                 {
@@ -188,6 +189,93 @@ namespace SixLabors.ImageSharp
             target = vector;
         }
 
+        /// <summary>
+        /// Computes the sum of vectors in the span referenced by <paramref name="sourceRow"/> weighted
+        /// by the kernel weight values.
+        /// Using this method the convolution filter is not applied to alpha in addition
+        /// to the color channels.
+        /// </summary>
+        /// <param name="state">The convolution kernel state.</param>
+        /// <param name="sourceRow">The source row.</param>
+        /// <param name="targetRow">The target row.</param>
+        /// <param name="kY">The current kernel row.</param>
+        /// <param name="bX">The interest x-bounds relative to the interest image.</param>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static void ConvolveRow3(
+            in ConvolutionState state,
+            Span<Vector4> sourceRow,
+            Span<Vector4> targetRow,
+            int kY,
+            int bX)
+        {
+            ReadOnlyKernel kernel = state.Kernel;
+            ref Vector4 sourceBase = ref MemoryMarshal.GetReference(sourceRow);
+            ref Vector4 targetBase = ref MemoryMarshal.GetReference(targetRow);
+
+            Numerics.Premultiply(sourceRow);
+
+            for (int x = 0; x < sourceRow.Length; x++)
+            {
+                Vector4 vector = default;
+                ref int sampleOffsetColumnBase = ref state.GetSampleColumn(x);
+
+                for (int kX = 0; kX < kernel.Columns; kX++)
+                {
+                    int offsetX = Unsafe.Add(ref sampleOffsetColumnBase, kX) - bX;
+                    Vector4 sample = Unsafe.Add(ref sourceBase, offsetX);
+                    vector += kernel[kY, kX] * sample;
+                }
+
+                ref Vector4 target = ref Unsafe.Add(ref targetBase, x);
+                vector.W = target.W;
+                Numerics.UnPremultiply(ref vector);
+                target = vector;
+            }
+        }
+
+        /// <summary>
+        /// Computes the sum of vectors in the span referenced by <paramref name="sourceRow"/> weighted
+        /// by the kernel weight values.
+        /// Using this method the convolution filter is applied to alpha in addition to the
+        /// color channels.
+        /// </summary>
+        /// <param name="state">The convolution kernel state.</param>
+        /// <param name="sourceRow">The source row.</param>
+        /// <param name="targetRow">The target row.</param>
+        /// <param name="kY">The current kernel row.</param>
+        /// <param name="bX">The interest x-bounds relative to the interest image.</param>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static void ConvolveRow4<TPixel>(
+            in ConvolutionState state,
+            Span<Vector4> sourceRow,
+            Span<Vector4> targetRow,
+            int kY,
+            int bX)
+            where TPixel : unmanaged, IPixel<TPixel>
+        {
+            ReadOnlyKernel kernel = state.Kernel;
+
+            ref Vector4 sourceBase = ref MemoryMarshal.GetReference(sourceRow);
+            ref Vector4 targetBase = ref MemoryMarshal.GetReference(targetRow);
+
+            Numerics.Premultiply(sourceRow);
+
+            for (int x = 0; x < sourceRow.Length; x++)
+            {
+                ref int sampleOffsetColumnBase = ref state.GetSampleColumn(x);
+                ref Vector4 target = ref Unsafe.Add(ref targetBase, x);
+
+                for (int kX = 0; kX < kernel.Columns; kX++)
+                {
+                    int offsetX = Unsafe.Add(ref sampleOffsetColumnBase, kX) - bX;
+                    Vector4 sample = Unsafe.Add(ref sourceBase, offsetX);
+                    target += kernel[kY, kX] * sample;
+                }
+            }
+
+            Numerics.UnPremultiply(targetRow);
+        }
+
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         private static void ConvolveImpl<TPixel>(
             in ConvolutionState state,
@@ -201,12 +289,12 @@ namespace SixLabors.ImageSharp
             int kernelHeight = kernel.Rows;
             int kernelWidth = kernel.Columns;
 
-            ref int sampleOffsetRowBase = ref state.GetSampleOffsetRow(row);
+            ref int sampleOffsetRowBase = ref state.GetSampleRow(row);
             for (int y = 0; y < kernelHeight; y++)
             {
                 int offsetY = Unsafe.Add(ref sampleOffsetRowBase, y);
                 ref TPixel sourceRowBase = ref MemoryMarshal.GetReference(sourcePixels.GetRowSpan(offsetY));
-                ref int sampleOffsetColumnBase = ref state.GetSampleOffsetColumn(column);
+                ref int sampleOffsetColumnBase = ref state.GetSampleColumn(column);
 
                 for (int x = 0; x < kernelWidth; x++)
                 {