From 0b4e7615ed9871d899d0e3aeb7671673cef0939a Mon Sep 17 00:00:00 2001
From: James Jackson-South <james_south@hotmail.com>
Date: Sat, 15 Apr 2017 13:25:27 +1000
Subject: [PATCH] Fix quantization altering the original image.

---
 src/ImageSharp/Quantizers/Quantizer.cs | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/src/ImageSharp/Quantizers/Quantizer.cs b/src/ImageSharp/Quantizers/Quantizer.cs
index bb856ccc5..492ec5f2b 100644
--- a/src/ImageSharp/Quantizers/Quantizer.cs
+++ b/src/ImageSharp/Quantizers/Quantizer.cs
@@ -68,7 +68,20 @@ namespace ImageSharp.Quantizers
 
                 // Collect the palette. Required before the second pass runs.
                 colorPalette = this.GetPalette();
-                this.SecondPass(pixels, quantizedPixels, width, height);
+
+                if (this.Dither)
+                {
+                    // We clone the image as we don't want to alter the original.
+                    using (Image<TColor> clone = new Image<TColor>(image))
+                    using (PixelAccessor<TColor> clonedPixels = clone.Lock())
+                    {
+                        this.SecondPass(clonedPixels, quantizedPixels, width, height);
+                    }
+                }
+                else
+                {
+                    this.SecondPass(pixels, quantizedPixels, width, height);
+                }
             }
 
             return new QuantizedImage<TColor>(width, height, colorPalette, quantizedPixels);