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using memory allocator to create the histogram and the cdf

pull/673/head
popow 8 years ago
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274db88720
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c1c58fa336
1 changed files with 27 additions and 32 deletions
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  1. 59
      src/ImageSharp/Processing/Processors/Normalization/AdaptiveHistEqualizationProcessor.cs

59
src/ImageSharp/Processing/Processors/Normalization/AdaptiveHistEqualizationProcessor.cs
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@ -2,7 +2,6 @@
// Licensed under the Apache License, Version 2.0.
using System;
using System.Collections.Generic;
using System.Numerics;
using SixLabors.ImageSharp.Advanced;
using SixLabors.ImageSharp.PixelFormats;
@ -36,27 +35,29 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization
Span<TPixel> pixels = source.GetPixelSpan();
int gridSize = 64;
int pixelsInGrid = gridSize * gridSize;
int contrastLimit = 5;
int halfGridSize = gridSize / 2;
int[] histogram = new int[this.LuminanceLevels];
int[] histogramCopy = new int[this.LuminanceLevels];
int[] cdf = new int[this.LuminanceLevels];
using (IBuffer<int> histogramBuffer = memoryAllocator.AllocateClean<int>(this.LuminanceLevels))
using (IBuffer<int> histogramBufferCopy = memoryAllocator.AllocateClean<int>(this.LuminanceLevels))
using (IBuffer<int> cdfBuffer = memoryAllocator.AllocateClean<int>(this.LuminanceLevels))
using (Buffer2D<TPixel> targetPixels = configuration.MemoryAllocator.Allocate2D<TPixel>(source.Width, source.Height))
{
Span<int> histogram = histogramBuffer.GetSpan();
Span<int> histogramCopy = histogramBufferCopy.GetSpan();
Span<int> cdf = cdfBuffer.GetSpan();
for (int x = halfGridSize; x < source.Width - halfGridSize; x++)
{
this.CleanArray(histogram);
this.CleanArray(cdf);
histogram.Clear();
var pixelsGrid = new List<TPixel>();
// Build the histogram of grayscale values for the current grid.
for (int dy = 0; dy < gridSize; dy++)
{
Span<TPixel> rowSpan = source.GetPixelRowSpan(dy).Slice(start: x - halfGridSize, length: gridSize);
pixelsGrid.AddRange(rowSpan.ToArray());
this.AddPixelsTooHistogram(rowSpan, histogram, this.LuminanceLevels);
}
this.CalcHistogram(pixelsGrid, histogram, this.LuminanceLevels);
for (int y = halfGridSize + 1; y < source.Height - halfGridSize; y++)
{
// Remove top most row from the histogram
@ -68,17 +69,16 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization
this.AddPixelsTooHistogram(rowSpan, histogram, this.LuminanceLevels);
// Clipping the histogram, but doing it on a copy to keep the original un-clipped values
histogram.AsSpan().CopyTo(histogramCopy);
histogram.CopyTo(histogramCopy);
this.ClipHistogram(histogramCopy, gridSize, contrastLimit);
cdf.Clear();
int cdfMin = this.CalculateCdf(cdf, histogramCopy);
double numberOfPixelsMinusCdfMin = (double)(pixelsGrid.Count - cdfMin);
double numberOfPixelsMinusCdfMin = (double)(pixelsInGrid - cdfMin);
// Map the current pixel to the new equalized value
int luminance = this.GetLuminance(pixels[(y * source.Width) + x], this.LuminanceLevels);
double luminanceEqualized = cdf[luminance] / numberOfPixelsMinusCdfMin;
targetPixels[x, y].PackFromVector4(new Vector4((float)luminanceEqualized));
this.CleanArray(cdf);
}
}
@ -88,7 +88,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization
/// <summary>
/// AHE tends to over amplify the contrast in near-constant regions of the image, since the histogram in such regions is highly concentrated.
/// Clipping the histogram is meant to reduce this effect, by cutting of histogram bin's which exceed a certain amount and redistribute
/// Clipping the histogram is meant to reduce this effect, by cutting of histogram bin's which exceed a certain amount and redistribute
/// the values over the clip limit to all other bins equally.
/// </summary>
/// <param name="histogram">The histogram to apply the clipping</param>
@ -125,6 +125,12 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization
return addToEachBin;
}
/// <summary>
/// Adds a row of grey values to the histogram.
/// </summary>
/// <param name="greyValues">The grey values to add</param>
/// <param name="histogram">The histogram</param>
/// <param name="luminanceLevels">The number of different luminance levels.</param>
private void AddPixelsTooHistogram(Span<TPixel> greyValues, Span<int> histogram, int luminanceLevels)
{
for (int i = 0; i < greyValues.Length; i++)
@ -134,6 +140,12 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization
}
}
/// <summary>
/// Removes a row of grey values from the histogram.
/// </summary>
/// <param name="greyValues">The grey values to remove</param>
/// <param name="histogram">The histogram</param>
/// <param name="luminanceLevels">The number of different luminance levels.</param>
private void RemovePixelsFromHistogram(Span<TPixel> greyValues, Span<int> histogram, int luminanceLevels)
{
for (int i = 0; i < greyValues.Length; i++)
@ -142,22 +154,5 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization
histogram[luminance]--;
}
}
private void CalcHistogram(List<TPixel> greyValues, Span<int> histogram, int luminanceLevels)
{
for (int i = 0; i < greyValues.Count; i++)
{
int luminance = this.GetLuminance(greyValues[i], luminanceLevels);
histogram[luminance]++;
}
}
private void CleanArray(Span<int> array)
{
for (int i = 0; i < array.Length; i++)
{
array[i] = 0;
}
}
}
}

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