From 5b1b8b11d3ff40f97d0ea49c23cc32ba1d48784f Mon Sep 17 00:00:00 2001 From: popow Date: Sun, 1 Jul 2018 13:29:46 +0200 Subject: [PATCH] changed the cdf to be the cumulative histogram --- .../HistogramEqualizationProcessor.cs | 34 +++++++++---------- 1 file changed, 16 insertions(+), 18 deletions(-) diff --git a/src/ImageSharp/Processing/Contrast/HistogramEqualizationProcessor.cs b/src/ImageSharp/Processing/Contrast/HistogramEqualizationProcessor.cs index 23a2d30ba..f23382d20 100644 --- a/src/ImageSharp/Processing/Contrast/HistogramEqualizationProcessor.cs +++ b/src/ImageSharp/Processing/Contrast/HistogramEqualizationProcessor.cs @@ -35,37 +35,34 @@ namespace SixLabors.ImageSharp.Processing.Contrast } } - int min = luminanceLevels - 1; - for (int i = 0; i < histogram.Length - 1; i++) + // calculate the cumulative distribution function which will be the cumulative histogram + int[] cdf = new int[luminanceLevels]; + int histSum = 0; + for (int i = 0; i < histogram.Length; i++) { - if (histogram[i] != 0) - { - min = i; - break; - } + histSum += histogram[i]; + cdf[i] = histSum; } - int max = 0; - for (int i = histogram.Length - 1; i > 0; i--) + int cdfMin = 0; + for (int i = 0; i < histogram.Length; i++) { if (histogram[i] != 0) { - max = i; + cdfMin = cdf[i]; break; } } - // calculate the cumulative distribution function - double[] cdf = new double[luminanceLevels]; - double sum = 0.0d; + int[] lut = new int[luminanceLevels]; for (int i = 0; i < histogram.Length; i++) { - double p = (double)histogram[i] / numberOfPixels; - sum += p; - cdf[i] = sum; + lut[i] = cdf[i] - cdfMin; } // apply the cdf to each pixel of the image + double numberOfPixelsMinusCdfMin = (double)(numberOfPixels - cdfMin); + int luminanceLevelsMinusOne = luminanceLevels - 1; for (int y = 0; y < source.Height; y++) { Span row = source.GetPixelRowSpan(y); @@ -74,8 +71,9 @@ namespace SixLabors.ImageSharp.Processing.Contrast TPixel sourcePixel = row[x]; sourcePixel.ToRgb24(ref rgb); int luminance = (int)((.2126F * rgb.R) + (.7152F * rgb.G) + (.0722F * rgb.B)); - byte luminanceEqualized = (byte)(cdf[luminance] * (luminanceLevels - 1)); - row[x].PackFromRgba32(new Rgba32(luminanceEqualized, luminanceEqualized, luminanceEqualized)); + double luminanceEqualized = (lut[luminance] / numberOfPixelsMinusCdfMin) * luminanceLevelsMinusOne; + luminanceEqualized = Math.Round(luminanceEqualized); + row[x].PackFromRgba32(new Rgba32((byte)luminanceEqualized, (byte)luminanceEqualized, (byte)luminanceEqualized)); } } }