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Cleanup and remove double cast.

af/merge-core
James Jackson-South 8 years ago
parent
d46ba5f00c
commit
ade60bd284
3 changed files with 38 additions and 25 deletions
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  1. 18
      src/ImageSharp/Processing/HistogramEqualizationExtension.cs
  2. 38
      src/ImageSharp/Processing/Processors/Normalization/HistogramEqualizationProcessor.cs
  3. 7
      tests/ImageSharp.Tests/Processing/Normalization/HistogramEqualizationTests.cs

18
src/ImageSharp/Processing/HistogramEqualizationExtension.cs
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@ -7,19 +7,29 @@ using SixLabors.ImageSharp.Processing.Processors.Normalization;
namespace SixLabors.ImageSharp.Processing
{
/// <summary>
/// Adds extension that allows applying an HistogramEqualization to the image.
/// Adds extension that allow the adjustment of the contrast of an image via its histogram.
/// </summary>
public static class HistogramEqualizationExtension
{
/// <summary>
/// Equalizes the histogram of an image to increases the global contrast using 65536 luminance levels.
/// </summary>
/// <typeparam name="TPixel">The pixel format.</typeparam>
/// <param name="source">The image this method extends.</param>
/// <returns>The <see cref="Image{TPixel}"/>.</returns>
public static IImageProcessingContext<TPixel> HistogramEqualization<TPixel>(this IImageProcessingContext<TPixel> source)
where TPixel : struct, IPixel<TPixel>
=> HistogramEqualization(source, 65536);
/// <summary>
/// Equalizes the histogram of an image to increases the global contrast.
/// </summary>
/// <typeparam name="TPixel">The pixel format.</typeparam>
/// <param name="source">The image this method extends.</param>
/// <param name="luminanceLevels">The number of different luminance levels. Typical values are 256 for 8-bit grayscale images
/// or 65536 for 16-bit grayscale images. Defaults to 65536.</param>
/// <returns>A histogram equalized grayscale image.</returns>
public static IImageProcessingContext<TPixel> HistogramEqualization<TPixel>(this IImageProcessingContext<TPixel> source, int luminanceLevels = 65536)
/// or 65536 for 16-bit grayscale images.</param>
/// <returns>The <see cref="Image{TPixel}"/>.</returns>
public static IImageProcessingContext<TPixel> HistogramEqualization<TPixel>(this IImageProcessingContext<TPixel> source, int luminanceLevels)
where TPixel : struct, IPixel<TPixel>
=> source.ApplyProcessor(new HistogramEqualizationProcessor<TPixel>(luminanceLevels));
}

38
src/ImageSharp/Processing/Processors/Normalization/HistogramEqualizationProcessor.cs
View File

@ -3,6 +3,7 @@
using System;
using System.Numerics;
using System.Runtime.CompilerServices;
using SixLabors.ImageSharp.Advanced;
using SixLabors.ImageSharp.PixelFormats;
using SixLabors.Memory;
@ -21,8 +22,8 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization
/// Initializes a new instance of the <see cref="HistogramEqualizationProcessor{TPixel}"/> class.
/// </summary>
/// <param name="luminanceLevels">The number of different luminance levels. Typical values are 256 for 8-bit grayscale images
/// or 65536 for 16-bit grayscale images. Defaults to 65536.</param>
public HistogramEqualizationProcessor(int luminanceLevels = 65536)
/// or 65536 for 16-bit grayscale images.</param>
public HistogramEqualizationProcessor(int luminanceLevels)
{
Guard.MustBeGreaterThan(luminanceLevels, 0, nameof(luminanceLevels));
@ -30,7 +31,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization
}
/// <summary>
/// Gets the luminance levels.
/// Gets the number of luminance levels.
/// </summary>
public int LuminanceLevels { get; }
@ -41,7 +42,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization
int numberOfPixels = source.Width * source.Height;
Span<TPixel> pixels = source.GetPixelSpan();
// build the histogram of the grayscale levels
// Build the histogram of the grayscale levels.
using (IBuffer<int> histogramBuffer = memoryAllocator.AllocateClean<int>(this.LuminanceLevels))
using (IBuffer<int> cdfBuffer = memoryAllocator.AllocateClean<int>(this.LuminanceLevels))
{
@ -53,33 +54,33 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization
histogram[luminance]++;
}
// calculate the cumulative distribution function, which will map each input pixel to a new value
// Calculate the cumulative distribution function, which will map each input pixel to a new value.
Span<int> cdf = cdfBuffer.GetSpan();
int cdfMin = this.CaluclateCdf(cdf, histogram);
int cdfMin = this.CalculateCdf(cdf, histogram);
// apply the cdf to each pixel of the image
double numberOfPixelsMinusCdfMin = (double)(numberOfPixels - cdfMin);
// Apply the cdf to each pixel of the image
float numberOfPixelsMinusCdfMin = numberOfPixels - cdfMin;
for (int i = 0; i < pixels.Length; i++)
{
TPixel sourcePixel = pixels[i];
int luminance = this.GetLuminance(sourcePixel, this.LuminanceLevels);
double luminanceEqualized = cdf[luminance] / numberOfPixelsMinusCdfMin;
float luminanceEqualized = cdf[luminance] / numberOfPixelsMinusCdfMin;
pixels[i].PackFromVector4(new Vector4((float)luminanceEqualized));
pixels[i].PackFromVector4(new Vector4(luminanceEqualized));
}
}
}
/// <summary>
/// Calculate the cumulative distribution function
/// Calculates the cumulative distribution function.
/// </summary>
/// <param name="cdf">The array holding the cdf</param>
/// <param name="histogram">The histogram of the input image</param>
/// <returns>The first none zero value of the cdf</returns>
private int CaluclateCdf(Span<int> cdf, Span<int> histogram)
/// <param name="cdf">The array holding the cdf.</param>
/// <param name="histogram">The histogram of the input image.</param>
/// <returns>The first none zero value of the cdf.</returns>
private int CalculateCdf(Span<int> cdf, Span<int> histogram)
{
// calculate the cumulative histogram
// Calculate the cumulative histogram
int histSum = 0;
for (int i = 0; i < histogram.Length; i++)
{
@ -87,7 +88,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization
cdf[i] = histSum;
}
// get the first none zero value of the cumulative histogram
// Get the first none zero value of the cumulative histogram
int cdfMin = 0;
for (int i = 0; i < histogram.Length; i++)
{
@ -98,7 +99,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization
}
}
// creating the lookup table: subtracting cdf min, so we do not need to do that inside the for loop
// Creating the lookup table: subtracting cdf min, so we do not need to do that inside the for loop
for (int i = 0; i < histogram.Length; i++)
{
cdf[i] = Math.Max(0, cdf[i] - cdfMin);
@ -112,6 +113,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization
/// </summary>
/// <param name="sourcePixel">The pixel to get the luminance from</param>
/// <param name="luminanceLevels">The number of luminance levels (256 for 8 bit, 65536 for 16 bit grayscale images)</param>
[MethodImpl(InliningOptions.ShortMethod)]
private int GetLuminance(TPixel sourcePixel, int luminanceLevels)
{
// Convert to grayscale using ITU-R Recommendation BT.709

7
tests/ImageSharp.Tests/Processing/Normalization/HistogramEqualizationTests.cs
View File

@ -14,7 +14,7 @@ namespace SixLabors.ImageSharp.Tests.Processing.Normalization
[InlineData(65536)]
public void HistogramEqualizationTest(int luminanceLevels)
{
// arrange
// Arrange
byte[] pixels = new byte[]
{
52, 55, 61, 59, 70, 61, 76, 61,
@ -26,6 +26,7 @@ namespace SixLabors.ImageSharp.Tests.Processing.Normalization
69, 85, 64, 58, 55, 61, 65, 83,
70, 87, 69, 68, 65, 73, 78, 90
};
var image = new Image<Rgba32>(8, 8);
for (int y = 0; y < 8; y++)
{
@ -48,10 +49,10 @@ namespace SixLabors.ImageSharp.Tests.Processing.Normalization
146, 206, 130, 117, 85, 166, 182, 215
};
// act
// Act
image.Mutate(x => x.HistogramEqualization(luminanceLevels));
// assert
// Assert
for (int y = 0; y < 8; y++)
{
for (int x = 0; x < 8; x++)

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