mirror of https://github.com/SixLabors/ImageSharp
popow
8 years ago
7 changed files with 228 additions and 97 deletions
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// Copyright (c) Six Labors and contributors.
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// Licensed under the Apache License, Version 2.0.
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using System; |
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using System.Numerics; |
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using SixLabors.ImageSharp.Advanced; |
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using SixLabors.ImageSharp.PixelFormats; |
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using SixLabors.Memory; |
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using SixLabors.Primitives; |
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namespace SixLabors.ImageSharp.Processing.Processors.Normalization |
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{ |
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/// <summary>
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/// Applies a global histogram equalization to the image.
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/// </summary>
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/// <typeparam name="TPixel">The pixel format.</typeparam>
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internal class GlobalHistogramEqualizationProcessor<TPixel> : HistogramEqualizationProcessor<TPixel> |
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where TPixel : struct, IPixel<TPixel> |
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{ |
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/// <summary>
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/// Initializes a new instance of the <see cref="GlobalHistogramEqualizationProcessor{TPixel}"/> class.
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/// </summary>
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/// <param name="luminanceLevels">The number of different luminance levels. Typical values are 256 for 8-bit grayscale images
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/// or 65536 for 16-bit grayscale images.</param>
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/// <param name="clipHistogram">Indicating whether to clip the histogram bins at a specific value.</param>
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/// <param name="clipLimit">The histogram clip limit. Histogram bins which exceed this limit, will be capped at this value.</param>
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public GlobalHistogramEqualizationProcessor(int luminanceLevels, bool clipHistogram, int clipLimit) |
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: base(luminanceLevels, clipHistogram, clipLimit) |
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{ |
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} |
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/// <inheritdoc/>
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protected override void OnFrameApply(ImageFrame<TPixel> source, Rectangle sourceRectangle, Configuration configuration) |
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{ |
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MemoryAllocator memoryAllocator = configuration.MemoryAllocator; |
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int numberOfPixels = source.Width * source.Height; |
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Span<TPixel> pixels = source.GetPixelSpan(); |
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// Build the histogram of the grayscale levels.
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using (IBuffer<int> histogramBuffer = memoryAllocator.AllocateClean<int>(this.LuminanceLevels)) |
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using (IBuffer<int> cdfBuffer = memoryAllocator.AllocateClean<int>(this.LuminanceLevels)) |
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{ |
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Span<int> histogram = histogramBuffer.GetSpan(); |
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for (int i = 0; i < pixels.Length; i++) |
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{ |
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TPixel sourcePixel = pixels[i]; |
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int luminance = this.GetLuminance(sourcePixel, this.LuminanceLevels); |
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histogram[luminance]++; |
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} |
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if (this.ClipHistogramEnabled) |
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{ |
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this.ClipHistogram(histogram, this.ClipLimit); |
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} |
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// Calculate the cumulative distribution function, which will map each input pixel to a new value.
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Span<int> cdf = cdfBuffer.GetSpan(); |
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int cdfMin = this.CalculateCdf(cdf, histogram); |
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// Apply the cdf to each pixel of the image
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float numberOfPixelsMinusCdfMin = numberOfPixels - cdfMin; |
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for (int i = 0; i < pixels.Length; i++) |
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{ |
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TPixel sourcePixel = pixels[i]; |
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int luminance = this.GetLuminance(sourcePixel, this.LuminanceLevels); |
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float luminanceEqualized = cdf[luminance] / numberOfPixelsMinusCdfMin; |
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pixels[i].PackFromVector4(new Vector4(luminanceEqualized)); |
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} |
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} |
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} |
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} |
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} |
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// Copyright (c) Six Labors and contributors.
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// Licensed under the Apache License, Version 2.0.
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namespace SixLabors.ImageSharp.Processing.Processors.Normalization |
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{ |
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/// <summary>
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/// Enumerates the different types of defined histogram equalization methods.
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/// </summary>
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public enum HistogramEqualizationMethod : int |
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{ |
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/// <summary>
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/// A global histogram equalization.
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/// </summary>
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Global, |
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/// <summary>
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/// Adaptive histogram equalization.
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/// </summary>
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Adaptive |
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} |
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} |
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// Copyright (c) Six Labors and contributors.
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// Licensed under the Apache License, Version 2.0.
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namespace SixLabors.ImageSharp.Processing.Processors.Normalization |
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{ |
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/// <summary>
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/// Data container providing the different options for the histogram equalization.
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/// </summary>
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public class HistogramEqualizationOptions |
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{ |
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/// <summary>
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/// Gets or sets the histogram equalization method to use. Defaults to global histogram equalization.
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/// </summary>
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public HistogramEqualizationMethod Method { get; set; } = HistogramEqualizationMethod.Global; |
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/// <summary>
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/// Gets or sets the number of different luminance levels. Typical values are 256 for 8-bit grayscale images
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/// or 65536 for 16-bit grayscale images. Defaults to 256.
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/// </summary>
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public int LuminanceLevels { get; set; } = 256; |
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/// <summary>
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/// Gets or sets a value indicating whether to clip the histogram bins at a specific value. Defaults to true.
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/// </summary>
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public bool ClipHistogram { get; set; } = true; |
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/// <summary>
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/// Gets or sets the histogram clip limit. Histogram bins which exceed this limit, will be capped at this value.
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/// Defaults to 80.
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/// </summary>
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public int ClipLimit { get; set; } = 80; |
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/// <summary>
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/// Gets or sets the size of the grid for the adaptive histogram equalization. Defaults to 32.
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/// </summary>
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public int GridSize { get; set; } = 32; |
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} |
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} |
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