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Moving sliding window from left to right instead of from top to bottom
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@brianpopow
brianpopow committed Jan 25, 2019
1 parent f2930c7 commit 8f19e5e
Showing 1 changed file with 49 additions and 46 deletions.
95 changes: 49 additions & 46 deletions src/ImageSharp/Processing/Processors/Normalization/AdaptiveHistEqualizationSWProcessor.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -51,43 +51,44 @@ protected override void OnFrameApply(ImageFrame<TPixel> source, Rectangle source
Span<TPixel> pixels = source.GetPixelSpan();

var parallelOptions = new ParallelOptions() { MaxDegreeOfParallelism = configuration.MaxDegreeOfParallelism };
int tileWidth = source.Width / this.Tiles;
int pixeInTile = tileWidth * tileWidth;
int halfTileWith = tileWidth / 2;
int tileHeight = source.Height / this.Tiles;
int pixeInTile = tileHeight * tileHeight;
int halfTileHeight = tileHeight / 2;
int halfTileWidth = halfTileHeight;
using (Buffer2D<TPixel> targetPixels = configuration.MemoryAllocator.Allocate2D<TPixel>(source.Width, source.Height))
{
Parallel.For(
0,
source.Width,
source.Height,
parallelOptions,
x =>
y =>
{
using (IMemoryOwner<int> histogramBuffer = memoryAllocator.Allocate<int>(this.LuminanceLevels, AllocationOptions.Clean))
using (IMemoryOwner<int> histogramBufferCopy = memoryAllocator.Allocate<int>(this.LuminanceLevels, AllocationOptions.Clean))
using (IMemoryOwner<int> cdfBuffer = memoryAllocator.Allocate<int>(this.LuminanceLevels, AllocationOptions.Clean))
using (IMemoryOwner<TPixel> pixelRowBuffer = memoryAllocator.Allocate<TPixel>(tileWidth, AllocationOptions.Clean))
using (IMemoryOwner<TPixel> pixelColumnBuffer = memoryAllocator.Allocate<TPixel>(tileHeight, AllocationOptions.Clean))
{
Span<int> histogram = histogramBuffer.GetSpan();
ref int histogramBase = ref MemoryMarshal.GetReference(histogram);
Span<int> histogramCopy = histogramBufferCopy.GetSpan();
ref int histogramCopyBase = ref MemoryMarshal.GetReference(histogramCopy);
ref int cdfBase = ref MemoryMarshal.GetReference(cdfBuffer.GetSpan());

Span<TPixel> pixelRow = pixelRowBuffer.GetSpan();
Span<TPixel> pixelColumn = pixelColumnBuffer.GetSpan();
int maxHistIdx = 0;

// Build the histogram of grayscale values for the current tile.
for (int dy = -halfTileWith; dy < halfTileWith; dy++)
for (int dx = -halfTileWidth; dx < halfTileWidth; dx++)
{
Span<TPixel> rowSpan = this.GetPixelRow(source, pixelRow, x - halfTileWith, dy, tileWidth);
int maxIdx = this.AddPixelsToHistogram(rowSpan, histogram, this.LuminanceLevels);
Span<TPixel> columnSpan = this.GetPixelColumn(source, pixelColumn, dx, y - halfTileHeight, tileHeight);
int maxIdx = this.AddPixelsToHistogram(columnSpan, histogram, this.LuminanceLevels);
if (maxIdx > maxHistIdx)
{
maxHistIdx = maxIdx;
}
}

for (int y = 0; y < source.Height; y++)
for (int x = 0; x < source.Width; x++)
{
if (this.ClipHistogramEnabled)
{
Expand All @@ -103,18 +104,18 @@ protected override void OnFrameApply(ImageFrame<TPixel> source, Rectangle source

float numberOfPixelsMinusCdfMin = pixeInTile - cdfMin;

// Map the current pixel to the new equalized value
// Map the current pixel to the new equalized value.
int luminance = GetLuminance(source[x, y], this.LuminanceLevels);
float luminanceEqualized = Unsafe.Add(ref cdfBase, luminance) / numberOfPixelsMinusCdfMin;
targetPixels[x, y].FromVector4(new Vector4(luminanceEqualized, luminanceEqualized, luminanceEqualized, source[x, y].ToVector4().W));

// Remove top most row from the histogram, mirroring rows which exceeds the borders.
Span<TPixel> rowSpan = this.GetPixelRow(source, pixelRow, x - halfTileWith, y - halfTileWith, tileWidth);
maxHistIdx = this.RemovePixelsFromHistogram(rowSpan, histogram, this.LuminanceLevels, maxHistIdx);
// Remove left most column from the histogram, mirroring columns which exceeds the borders of the image.
Span<TPixel> columnSpan = this.GetPixelColumn(source, pixelColumn, x - halfTileWidth, y - halfTileHeight, tileHeight);
maxHistIdx = this.RemovePixelsFromHistogram(columnSpan, histogram, this.LuminanceLevels, maxHistIdx);

// Add new bottom row to the histogram, mirroring rows which exceeds the borders.
rowSpan = this.GetPixelRow(source, pixelRow, x - halfTileWith, y + halfTileWith, tileWidth);
int maxIdx = this.AddPixelsToHistogram(rowSpan, histogram, this.LuminanceLevels);
// Add new right column to the histogram, mirroring columns which exceeds the borders of the image.
columnSpan = this.GetPixelColumn(source, pixelColumn, x + halfTileWidth, y - halfTileHeight, tileHeight);
int maxIdx = this.AddPixelsToHistogram(columnSpan, histogram, this.LuminanceLevels);
if (maxIdx > maxHistIdx)
{
maxHistIdx = maxIdx;
Expand All @@ -128,62 +129,64 @@ protected override void OnFrameApply(ImageFrame<TPixel> source, Rectangle source
}

/// <summary>
/// Get the a pixel row at a given position with a length of the tile width. Mirrors pixels which exceeds the edges.
/// Get the a pixel column at a given position with the size of the tile height. Mirrors pixels which exceeds the edges of the image.
/// </summary>
/// <param name="source">The source image.</param>
/// <param name="rowPixels">Pre-allocated pixel row span of the size of a tile width.</param>
/// <param name="columnPixels">Pre-allocated pixel row span of the size of a tile height.</param>
/// <param name="x">The x position.</param>
/// <param name="y">The y position.</param>
/// <param name="tileWidth">The width in pixels of a tile.</param>
/// <param name="tileHeight">The height in pixels of a tile.</param>
/// <returns>A pixel row of the length of the tile width.</returns>
private Span<TPixel> GetPixelRow(ImageFrame<TPixel> source, Span<TPixel> rowPixels, int x, int y, int tileWidth)
private Span<TPixel> GetPixelColumn(ImageFrame<TPixel> source, Span<TPixel> columnPixels, int x, int y, int tileHeight)
{
if (y < 0)
if (x < 0)
{
y = Math.Abs(y);
x = Math.Abs(x);
}
else if (y >= source.Height)
else if (x >= source.Width)
{
int diff = y - source.Height;
y = source.Height - diff - 1;
int diff = x - source.Width;
x = source.Width - diff - 1;
}

// Special cases for the left and the right border where GetPixelRowSpan can not be used
if (x < 0)
int idx = 0;
columnPixels.Clear();
if (y < 0)
{
rowPixels.Clear();
int idx = 0;
for (int dx = x; dx < x + tileWidth; dx++)
columnPixels.Clear();
for (int dy = y; dy < y + tileHeight; dy++)
{
rowPixels[idx] = source[Math.Abs(dx), y];
columnPixels[idx] = source[x, Math.Abs(dy)];
idx++;
}

return rowPixels;
}
else if (x + tileWidth > source.Width)
else if (y + tileHeight > source.Height)
{
rowPixels.Clear();
int idx = 0;
for (int dx = x; dx < x + tileWidth; dx++)
for (int dy = y; dy < y + tileHeight; dy++)
{
if (dx >= source.Width)
if (dy >= source.Height)
{
int diff = dx - source.Width;
rowPixels[idx] = source[dx - diff - 1, y];
int diff = dy - source.Height;
columnPixels[idx] = source[x, dy - diff - 1];
}
else
{
rowPixels[idx] = source[dx, y];
columnPixels[idx] = source[x, dy];
}

idx++;
}

return rowPixels;
}
else
{
for (int dy = y; dy < y + tileHeight; dy++)
{
columnPixels[idx] = source[x, dy];
idx++;
}
}

return source.GetPixelRowSpan(y).Slice(start: x, length: tileWidth);
return columnPixels;
}

/// <summary>
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