Addition of Breadley AdaptiveThreshold

src/ImageSharp/Processing/AdaptiveThresholdExtensions.cs

@@ -0,0 +1,74 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+using SixLabors.ImageSharp.Processing.Processors.Binarization;
+
+namespace SixLabors.ImageSharp.Processing
+{
+    /// <summary>
+    /// Extensions to perform AdaptiveThreshold through Mutator.
+    /// </summary>
+    public static class AdaptiveThresholdExtensions
+    {
+        /// <summary>
+        /// Applies Bradley Adaptive Threshold to the image.
+        /// </summary>
+        /// <param name="source">The image this method extends.</param>
+        /// <returns>The <see cref="Image{TPixel}"/>.</returns>
+        public static IImageProcessingContext AdaptiveThreshold(this IImageProcessingContext source)
+            => source.ApplyProcessor(new AdaptiveThresholdProcessor());
+
+        /// <summary>
+        /// Applies Bradley Adaptive Threshold to the image.
+        /// </summary>
+        /// <param name="source">The image this method extends.</param>
+        /// <param name="thresholdLimit">Threshold limit (0.0-1.0) to consider for binarization.</param>
+        /// <returns>The <see cref="Image{TPixel}"/>.</returns>
+        public static IImageProcessingContext AdaptiveThreshold(this IImageProcessingContext source, float thresholdLimit)
+            => source.ApplyProcessor(new AdaptiveThresholdProcessor(thresholdLimit));
+
+        /// <summary>
+        /// Applies Bradley Adaptive Threshold to the image.
+        /// </summary>
+        /// <param name="source">The image this method extends.</param>
+        /// <param name="upper">Upper (white) color for thresholding.</param>
+        /// <param name="lower">Lower (black) color for thresholding.</param>
+        /// <returns>The <see cref="Image{TPixel}"/>.</returns>
+        public static IImageProcessingContext AdaptiveThreshold(this IImageProcessingContext source, Color upper, Color lower)
+            => source.ApplyProcessor(new AdaptiveThresholdProcessor(upper, lower));
+
+        /// <summary>
+        /// Applies Bradley Adaptive Threshold to the image.
+        /// </summary>
+        /// <param name="source">The image this method extends.</param>
+        /// <param name="upper">Upper (white) color for thresholding.</param>
+        /// <param name="lower">Lower (black) color for thresholding.</param>
+        /// <param name="thresholdLimit">Threshold limit (0.0-1.0) to consider for binarization.</param>
+        /// <returns>The <see cref="Image{TPixel}"/>.</returns>
+        public static IImageProcessingContext AdaptiveThreshold(this IImageProcessingContext source, Color upper, Color lower, float thresholdLimit)
+            => source.ApplyProcessor(new AdaptiveThresholdProcessor(upper, lower, thresholdLimit));
+
+        /// <summary>
+        /// Applies Bradley Adaptive Threshold to the image.
+        /// </summary>
+        /// <param name="source">The image this method extends.</param>
+        /// <param name="upper">Upper (white) color for thresholding.</param>
+        /// <param name="lower">Lower (black) color for thresholding</param>
+        /// <param name="rectangle">Rectangle region to apply the processor on.</param>
+        /// <returns>The <see cref="Image{TPixel}"/>.</returns>
+        public static IImageProcessingContext AdaptiveThreshold(this IImageProcessingContext source, Color upper, Color lower, Rectangle rectangle)
+            => source.ApplyProcessor(new AdaptiveThresholdProcessor(upper, lower), rectangle);
+
+        /// <summary>
+        /// Applies Bradley Adaptive Threshold to the image.
+        /// </summary>
+        /// <param name="source">The image this method extends.</param>
+        /// <param name="upper">Upper (white) color for thresholding.</param>
+        /// <param name="lower">Lower (black) color for thresholding</param>
+        /// <param name="thresholdLimit">Threshold limit (0.0-1.0) to consider for binarization.</param>
+        /// <param name="rectangle">Rectangle region to apply the processor on.</param>
+        /// <returns>The <see cref="Image{TPixel}"/>.</returns>
+        public static IImageProcessingContext AdaptiveThreshold(this IImageProcessingContext source, Color upper, Color lower, float thresholdLimit, Rectangle rectangle)
+            => source.ApplyProcessor(new AdaptiveThresholdProcessor(upper, lower, thresholdLimit), rectangle);
+    }
+}

src/ImageSharp/Processing/Processors/Binarization/AdaptiveThresholdProcessor.cs

@@ -0,0 +1,77 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+using SixLabors.ImageSharp.PixelFormats;
+
+namespace SixLabors.ImageSharp.Processing.Processors.Binarization
+{
+    /// <summary>
+    /// Performs Bradley Adaptive Threshold filter against an image.
+    /// </summary>
+    /// <remarks>
+    /// Implements "Adaptive Thresholding Using the Integral Image",
+    /// see paper: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.420.7883&amp;rep=rep1&amp;type=pdf
+    /// </remarks>
+    public class AdaptiveThresholdProcessor : IImageProcessor
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="AdaptiveThresholdProcessor"/> class.
+        /// </summary>
+        public AdaptiveThresholdProcessor()
+            : this(Color.White, Color.Black, 0.85f)
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="AdaptiveThresholdProcessor"/> class.
+        /// </summary>
+        /// <param name="thresholdLimit">Threshold limit.</param>
+        public AdaptiveThresholdProcessor(float thresholdLimit)
+            : this(Color.White, Color.Black, thresholdLimit)
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="AdaptiveThresholdProcessor"/> class.
+        /// </summary>
+        /// <param name="upper">Color for upper threshold.</param>
+        /// <param name="lower">Color for lower threshold.</param>
+        public AdaptiveThresholdProcessor(Color upper, Color lower)
+            : this(upper, lower, 0.85f)
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="AdaptiveThresholdProcessor"/> class.
+        /// </summary>
+        /// <param name="upper">Color for upper threshold.</param>
+        /// <param name="lower">Color for lower threshold.</param>
+        /// <param name="thresholdLimit">Threshold limit.</param>
+        public AdaptiveThresholdProcessor(Color upper, Color lower, float thresholdLimit)
+        {
+            this.Upper = upper;
+            this.Lower = lower;
+            this.ThresholdLimit = thresholdLimit;
+        }
+
+        /// <summary>
+        /// Gets or sets upper color limit for thresholding.
+        /// </summary>
+        public Color Upper { get; set; }
+
+        /// <summary>
+        /// Gets or sets lower color limit for threshold.
+        /// </summary>
+        public Color Lower { get; set; }
+
+        /// <summary>
+        /// Gets or sets the value for threshold limit.
+        /// </summary>
+        public float ThresholdLimit { get; set; }
+
+        /// <inheritdoc />
+        public IImageProcessor<TPixel> CreatePixelSpecificProcessor<TPixel>(Configuration configuration, Image<TPixel> source, Rectangle sourceRectangle)
+            where TPixel : unmanaged, IPixel<TPixel>
+            => new AdaptiveThresholdProcessor<TPixel>(configuration, this, source, sourceRectangle);
+    }
+}

src/ImageSharp/Processing/Processors/Binarization/AdaptiveThresholdProcessor{TPixel}.cs

@@ -0,0 +1,160 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+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.Binarization
+{
+    /// <summary>
+    /// Performs Bradley Adaptive Threshold filter against an image.
+    /// </summary>
+    internal class AdaptiveThresholdProcessor<TPixel> : ImageProcessor<TPixel>
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        private readonly AdaptiveThresholdProcessor definition;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="AdaptiveThresholdProcessor{TPixel}"/> class.
+        /// </summary>
+        /// <param name="configuration">The configuration which allows altering default behaviour or extending the library.</param>
+        /// <param name="definition">The <see cref="AdaptiveThresholdProcessor"/> defining the processor parameters.</param>
+        /// <param name="source">The source <see cref="Image{TPixel}"/> for the current processor instance.</param>
+        /// <param name="sourceRectangle">The source area to process for the current processor instance.</param>
+        public AdaptiveThresholdProcessor(Configuration configuration, AdaptiveThresholdProcessor definition, Image<TPixel> source, Rectangle sourceRectangle)
+            : base(configuration, source, sourceRectangle)
+        {
+            this.definition = definition;
+        }
+
+        /// <inheritdoc/>
+        protected override void OnFrameApply(ImageFrame<TPixel> source)
+        {
+            var intersect = Rectangle.Intersect(this.SourceRectangle, source.Bounds());
+
+            Configuration configuration = this.Configuration;
+            TPixel upper = this.definition.Upper.ToPixel<TPixel>();
+            TPixel lower = this.definition.Lower.ToPixel<TPixel>();
+            float thresholdLimit = this.definition.ThresholdLimit;
+
+            int startY = intersect.Y;
+            int endY = intersect.Bottom;
+            int startX = intersect.X;
+            int endX = intersect.Right;
+
+            int width = intersect.Width;
+            int height = intersect.Height;
+
+            // ClusterSize defines the size of cluster to used to check for average. Tweaked to support up to 4k wide pixels and not more. 4096 / 16 is 256 thus the '-1'
+            byte clusterSize = (byte)Math.Truncate((width / 16f) - 1);
+
+            // Using pooled 2d buffer for integer image table and temp memory to hold Rgb24 converted pixel data.
+            using (Buffer2D<ulong> intImage = this.Configuration.MemoryAllocator.Allocate2D<ulong>(width, height))
+            {
+                Rgba32 rgb = default;
+                for (int x = startX; x < endX; x++)
+                {
+                    ulong sum = 0;
+                    for (int y = startY; y < endY; y++)
+                    {
+                        Span<TPixel> row = source.GetPixelRowSpan(y);
+                        ref TPixel rowRef = ref MemoryMarshal.GetReference(row);
+                        ref TPixel color = ref Unsafe.Add(ref rowRef, x);
+                        color.ToRgba32(ref rgb);
+
+                        sum += (ulong)(rgb.R + rgb.G + rgb.G);
+                        if (x - startX != 0)
+                        {
+                            intImage[x - startX, y - startY] = intImage[x - startX - 1, y - startY] + sum;
+                        }
+                        else
+                        {
+                            intImage[x - startX, y - startY] = sum;
+                        }
+                    }
+                }
+
+                var operation = new RowOperation(intersect, source, intImage, upper, lower, thresholdLimit, clusterSize, startX, endX, startY);
+                ParallelRowIterator.IterateRows(
+                    configuration,
+                    intersect,
+                    in operation);
+            }
+        }
+
+        private readonly struct RowOperation : IRowOperation
+        {
+            private readonly Rectangle bounds;
+            private readonly ImageFrame<TPixel> source;
+            private readonly Buffer2D<ulong> intImage;
+            private readonly TPixel upper;
+            private readonly TPixel lower;
+            private readonly float thresholdLimit;
+            private readonly int startX;
+            private readonly int endX;
+            private readonly int startY;
+            private readonly byte clusterSize;
+
+            [MethodImpl(InliningOptions.ShortMethod)]
+            public RowOperation(
+                Rectangle bounds,
+                ImageFrame<TPixel> source,
+                Buffer2D<ulong> intImage,
+                TPixel upper,
+                TPixel lower,
+                float thresholdLimit,
+                byte clusterSize,
+                int startX,
+                int endX,
+                int startY)
+            {
+                this.bounds = bounds;
+                this.source = source;
+                this.intImage = intImage;
+                this.upper = upper;
+                this.lower = lower;
+                this.thresholdLimit = thresholdLimit;
+                this.startX = startX;
+                this.endX = endX;
+                this.startY = startY;
+                this.clusterSize = clusterSize;
+            }
+
+            /// <inheritdoc/>
+            [MethodImpl(InliningOptions.ShortMethod)]
+            public void Invoke(int y)
+            {
+                Rgba32 rgb = default;
+                Span<TPixel> pixelRow = this.source.GetPixelRowSpan(y);
+
+                for (int x = this.startX; x < this.endX; x++)
+                {
+                    TPixel pixel = pixelRow[x];
+                    pixel.ToRgba32(ref rgb);
+
+                    var x1 = Math.Max(x - this.startX - this.clusterSize + 1, 0);
+                    var x2 = Math.Min(x - this.startX + this.clusterSize + 1, this.bounds.Width - 1);
+                    var y1 = Math.Max(y - this.startY - this.clusterSize + 1, 0);
+                    var y2 = Math.Min(y - this.startY + this.clusterSize + 1, this.bounds.Height - 1);
+
+                    var count = (uint)((x2 - x1) * (y2 - y1));
+                    var sum = (long)Math.Min(this.intImage[x2, y2] - this.intImage[x1, y2] - this.intImage[x2, y1] + this.intImage[x1, y1], long.MaxValue);
+
+                    if ((rgb.R + rgb.G + rgb.B) * count <= sum * this.thresholdLimit)
+                    {
+                        this.source[x, y] = this.lower;
+                    }
+                    else
+                    {
+                        this.source[x, y] = this.upper;
+                    }
+                }
+            }
+        }
+    }
+}