diff --git a/src/ImageSharp/Processing/Processors/Normalization/AdaptiveHistogramEqualizationProcessor{TPixel}.cs b/src/ImageSharp/Processing/Processors/Normalization/AdaptiveHistogramEqualizationProcessor{TPixel}.cs index 08222d4ca..4cda4030f 100644 --- a/src/ImageSharp/Processing/Processors/Normalization/AdaptiveHistogramEqualizationProcessor{TPixel}.cs +++ b/src/ImageSharp/Processing/Processors/Normalization/AdaptiveHistogramEqualizationProcessor{TPixel}.cs @@ -73,10 +73,12 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization var tileYStartPositions = new List<(int y, int cdfY)>(); int cdfY = 0; - for (int y = halfTileHeight; y < sourceHeight - halfTileHeight; y += tileHeight) + int yStart = halfTileHeight; + for (int tile = 0; tile < tileCount - 1; tile++) { - tileYStartPositions.Add((y, cdfY)); + tileYStartPositions.Add((yStart, cdfY)); cdfY++; + yStart += tileHeight; } Parallel.For( @@ -92,7 +94,8 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization ref TPixel sourceBase = ref source.GetPixelReference(0, 0); int cdfX = 0; - for (int x = halfTileWidth; x < sourceWidth - halfTileWidth; x += tileWidth) + int x = halfTileWidth; + for (int tile = 0; tile < tileCount - 1; tile++) { int tileY = 0; int yEnd = Math.Min(y + tileHeight, sourceHeight); @@ -125,24 +128,25 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization } cdfX++; + x += tileWidth; } }); ref TPixel pixelsBase = ref source.GetPixelReference(0, 0); // Fix left column - ProcessBorderColumn(ref pixelsBase, cdfData, 0, sourceWidth, sourceHeight, tileWidth, tileHeight, xStart: 0, xEnd: halfTileWidth, luminanceLevels); + ProcessBorderColumn(ref pixelsBase, cdfData, 0, sourceWidth, sourceHeight, this.Tiles, tileHeight, xStart: 0, xEnd: halfTileWidth, luminanceLevels); // Fix right column int rightBorderStartX = ((this.Tiles - 1) * tileWidth) + halfTileWidth; - ProcessBorderColumn(ref pixelsBase, cdfData, this.Tiles - 1, sourceWidth, sourceHeight, tileWidth, tileHeight, xStart: rightBorderStartX, xEnd: sourceWidth, luminanceLevels); + ProcessBorderColumn(ref pixelsBase, cdfData, this.Tiles - 1, sourceWidth, sourceHeight, this.Tiles, tileHeight, xStart: rightBorderStartX, xEnd: sourceWidth, luminanceLevels); // Fix top row - ProcessBorderRow(ref pixelsBase, cdfData, 0, sourceWidth, tileWidth, yStart: 0, yEnd: halfTileHeight, luminanceLevels); + ProcessBorderRow(ref pixelsBase, cdfData, 0, sourceWidth, this.Tiles, tileWidth, yStart: 0, yEnd: halfTileHeight, luminanceLevels); // Fix bottom row int bottomBorderStartY = ((this.Tiles - 1) * tileHeight) + halfTileHeight; - ProcessBorderRow(ref pixelsBase, cdfData, this.Tiles - 1, sourceWidth, tileWidth, yStart: bottomBorderStartY, yEnd: sourceHeight, luminanceLevels); + ProcessBorderRow(ref pixelsBase, cdfData, this.Tiles - 1, sourceWidth, this.Tiles, tileWidth, yStart: bottomBorderStartY, yEnd: sourceHeight, luminanceLevels); // Left top corner ProcessCornerTile(ref pixelsBase, cdfData, sourceWidth, 0, 0, xStart: 0, xEnd: halfTileWidth, yStart: 0, yEnd: halfTileHeight, luminanceLevels); @@ -206,7 +210,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization /// The X index of the lookup table to use. /// The source image width. /// The source image height. - /// The width of a tile. + /// The number of vertical tiles. /// The height of a tile. /// X start position in the image. /// X end position of the image. @@ -220,7 +224,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization int cdfX, int sourceWidth, int sourceHeight, - int tileWidth, + int tileCount, int tileHeight, int xStart, int xEnd, @@ -229,7 +233,8 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization int halfTileHeight = tileHeight / 2; int cdfY = 0; - for (int y = halfTileHeight; y < sourceHeight - halfTileHeight; y += tileHeight) + int y = halfTileHeight; + for (int tile = 0; tile < tileCount - 1; tile++) { int yLimit = Math.Min(y + tileHeight, sourceHeight - 1); int tileY = 0; @@ -247,6 +252,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization } cdfY++; + y += tileHeight; } } @@ -257,6 +263,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization /// The pre-computed lookup tables to remap the grey values for each tiles. /// The Y index of the lookup table to use. /// The source image width. + /// The number of horizontal tiles. /// The width of a tile. /// Y start position in the image. /// Y end position of the image. @@ -269,6 +276,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization CdfTileData cdfData, int cdfY, int sourceWidth, + int tileCount, int tileWidth, int yStart, int yEnd, @@ -277,7 +285,8 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization int halfTileWidth = tileWidth / 2; int cdfX = 0; - for (int x = halfTileWidth; x < sourceWidth - halfTileWidth; x += tileWidth) + int x = halfTileWidth; + for (int tile = 0; tile < tileCount - 1; tile++) { for (int dy = yStart; dy < yEnd; dy++) { @@ -294,6 +303,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization } cdfX++; + x += tileWidth; } } diff --git a/src/ImageSharp/Processing/Processors/Normalization/HistogramEqualizationOptions.cs b/src/ImageSharp/Processing/Processors/Normalization/HistogramEqualizationOptions.cs index 1d9d5c986..8ddb4834d 100644 --- a/src/ImageSharp/Processing/Processors/Normalization/HistogramEqualizationOptions.cs +++ b/src/ImageSharp/Processing/Processors/Normalization/HistogramEqualizationOptions.cs @@ -1,4 +1,4 @@ -// Copyright (c) Six Labors and contributors. +// Copyright (c) Six Labors and contributors. // Licensed under the Apache License, Version 2.0. namespace SixLabors.ImageSharp.Processing.Processors.Normalization @@ -25,7 +25,9 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization public int LuminanceLevels { get; set; } = 256; /// - /// Gets or sets a value indicating whether to clip the histogram bins at a specific value. Defaults to false. + /// Gets or sets a value indicating whether to clip the histogram bins at a specific value. + /// It is recommended to use clipping when the AdaptiveTileInterpolation method is used, to suppress artifacts which can occur on the borders of the tiles. + /// Defaults to false. /// public bool ClipHistogram { get; set; } = false; diff --git a/tests/ImageSharp.Tests/Processing/Normalization/HistogramEqualizationTests.cs b/tests/ImageSharp.Tests/Processing/Normalization/HistogramEqualizationTests.cs index 5d8a155f0..c71232524 100644 --- a/tests/ImageSharp.Tests/Processing/Normalization/HistogramEqualizationTests.cs +++ b/tests/ImageSharp.Tests/Processing/Normalization/HistogramEqualizationTests.cs @@ -9,6 +9,7 @@ using Xunit; namespace SixLabors.ImageSharp.Tests.Processing.Normalization { + // ReSharper disable InconsistentNaming public class HistogramEqualizationTests { private static readonly ImageComparer ValidatorComparer = ImageComparer.TolerantPercentage(0.0456F); @@ -113,5 +114,30 @@ namespace SixLabors.ImageSharp.Tests.Processing.Normalization image.CompareToReferenceOutput(ValidatorComparer, provider); } } + + /// + /// This is regression test for a bug with the calculation of the y-start positions, + /// where it could happen that one too much start position was calculated in some cases. + /// See: https://github.com/SixLabors/ImageSharp/pull/984 + /// + [Theory] + [WithTestPatternImages(110, 110, PixelTypes.Rgba32)] + [WithTestPatternImages(170, 170, PixelTypes.Rgba32)] + public void Issue984(TestImageProvider provider) + where TPixel : struct, IPixel + { + using (Image image = provider.GetImage()) + { + var options = new HistogramEqualizationOptions() + { + Method = HistogramEqualizationMethod.AdaptiveTileInterpolation, + LuminanceLevels = 256, + ClipHistogram = true, + NumberOfTiles = 10 + }; + image.Mutate(x => x.HistogramEqualization(options)); + image.DebugSave(provider); + } + } } }