From 62b3ee3c49b38b868b5e2f615045df9030e0e33f Mon Sep 17 00:00:00 2001
From: popow <popow@gmx.de>
Date: Sun, 12 Aug 2018 17:18:20 +0200
Subject: [PATCH] removed unnecessary loops in CalculateCdf, fixed typo in
 method name AddPixelsToHistogram

---
 .../AdaptiveHistEqualizationProcessor.cs      |  7 ++---
 .../HistogramEqualizationProcessor.cs         | 30 +++++--------------
 2 files changed, 11 insertions(+), 26 deletions(-)

diff --git a/src/ImageSharp/Processing/Processors/Normalization/AdaptiveHistEqualizationProcessor.cs b/src/ImageSharp/Processing/Processors/Normalization/AdaptiveHistEqualizationProcessor.cs
index 12c897183f..5e3dea6c6f 100644
--- a/src/ImageSharp/Processing/Processors/Normalization/AdaptiveHistEqualizationProcessor.cs
+++ b/src/ImageSharp/Processing/Processors/Normalization/AdaptiveHistEqualizationProcessor.cs
@@ -3,7 +3,6 @@
 
 using System;
 using System.Numerics;
-using System.Threading.Tasks;
 using SixLabors.ImageSharp.Advanced;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
@@ -70,7 +69,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization
                             for (int dy = -halfGridSize; dy < halfGridSize; dy++)
                             {
                                 Span<TPixel> rowSpan = this.GetPixelRow(source, (int)x - halfGridSize, dy, this.GridSize);
-                                int maxIdx = this.AddPixelsTooHistogram(rowSpan, histogram, this.LuminanceLevels);
+                                int maxIdx = this.AddPixelsToHistogram(rowSpan, histogram, this.LuminanceLevels);
                                 if (maxIdx > maxHistIdx)
                                 {
                                     maxHistIdx = maxIdx;
@@ -101,7 +100,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization
 
                                 // Add new bottom row to the histogram, mirroring rows which exceeds the borders.
                                 rowSpan = this.GetPixelRow(source, x - halfGridSize, y + halfGridSize, this.GridSize);
-                                int maxIdx = this.AddPixelsTooHistogram(rowSpan, histogram, this.LuminanceLevels);
+                                int maxIdx = this.AddPixelsToHistogram(rowSpan, histogram, this.LuminanceLevels);
                                 if (maxIdx > maxHistIdx)
                                 {
                                     maxHistIdx = maxIdx;
@@ -179,7 +178,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization
         /// <param name="histogram">The histogram</param>
         /// <param name="luminanceLevels">The number of different luminance levels.</param>
         /// <returns>The maximum index where a value was changed.</returns>
-        private int AddPixelsTooHistogram(Span<TPixel> greyValues, Span<int> histogram, int luminanceLevels)
+        private int AddPixelsToHistogram(Span<TPixel> greyValues, Span<int> histogram, int luminanceLevels)
         {
             int maxIdx = 0;
             for (int idx = 0; idx < greyValues.Length; idx++)
diff --git a/src/ImageSharp/Processing/Processors/Normalization/HistogramEqualizationProcessor.cs b/src/ImageSharp/Processing/Processors/Normalization/HistogramEqualizationProcessor.cs
index a86c8b6183..e52aff1e76 100644
--- a/src/ImageSharp/Processing/Processors/Normalization/HistogramEqualizationProcessor.cs
+++ b/src/ImageSharp/Processing/Processors/Normalization/HistogramEqualizationProcessor.cs
@@ -2,11 +2,6 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System;
-using System.Buffers;
-using System.Numerics;
-using System.Runtime.CompilerServices;
-using SixLabors.ImageSharp.Advanced;
-using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;
 
 namespace SixLabors.ImageSharp.Processing.Processors.Normalization
@@ -59,29 +54,20 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization
         /// <returns>The first none zero value of the cdf.</returns>
         protected int CalculateCdf(Span<int> cdf, Span<int> histogram, int maxIdx)
         {
-            // Calculate the cumulative histogram
             int histSum = 0;
-            for (int i = 0; i <= maxIdx; i++)
-            {
-                histSum += histogram[i];
-                cdf[i] = histSum;
-            }
-
-            // Get the first none zero value of the cumulative histogram
             int cdfMin = 0;
+            bool cdfMinFound = false;
             for (int i = 0; i <= maxIdx; i++)
             {
-                if (cdf[i] != 0)
+                histSum += histogram[i];
+                if (!cdfMinFound && histSum != 0)
                 {
-                    cdfMin = cdf[i];
-                    break;
+                    cdfMin = histSum;
+                    cdfMinFound = true;
                 }
-            }
 
-            // Creating the lookup table: subtracting cdf min, so we do not need to do that inside the for loop
-            for (int i = 0; i <= maxIdx; i++)
-            {
-                cdf[i] = Math.Max(0, cdf[i] - cdfMin);
+                // Creating the lookup table: subtracting cdf min, so we do not need to do that inside the for loop
+                cdf[i] = Math.Max(0, histSum - cdfMin);
             }
 
             return cdfMin;
@@ -108,7 +94,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Normalization
                 }
             }
 
-            int addToEachBin = (int)Math.Floor(sumOverClip / (double)this.LuminanceLevels);
+            int addToEachBin = sumOverClip > 0 ? (int)Math.Floor(sumOverClip / (double)this.LuminanceLevels) : 0;
             if (addToEachBin > 0)
             {
                 for (int i = 0; i < histogram.Length; i++)