Optimize Contrast

src/ImageSharp/Processing/Processors/Effects/ContrastProcessor.cs

@@ -45,8 +45,8 @@ namespace ImageSharp.Processing.Processors
             int endY = sourceRectangle.Bottom;
             int startX = sourceRectangle.X;
             int endX = sourceRectangle.Right;
-            Vector4 contrastVector = new Vector4(contrast, contrast, contrast, 1);
+            var contrastVector = new Vector4(contrast, contrast, contrast, 1);
-            Vector4 shiftVector = new Vector4(.5F, .5F, .5F, 1);
+            var shiftVector = new Vector4(.5F, .5F, .5F, 1);
 
             // Align start/end positions.
             int minX = Math.Max(0, startX);
@@ -65,8 +65,6 @@ namespace ImageSharp.Processing.Processors
                 startY = 0;
             }
 
-            using (PixelAccessor<TPixel> sourcePixels = source.Lock())
-            {
             Parallel.For(
                 minY,
                 maxY,
@@ -74,20 +72,21 @@ namespace ImageSharp.Processing.Processors
                 y =>
                     {
                         int offsetY = y - startY;
+                        Span<TPixel> row = source.GetRowSpan(y - startY);
+
                         for (int x = minX; x < maxX; x++)
                         {
                             int offsetX = x - startX;
+                            ref TPixel pixel = ref row[x - startX];
 
-                                Vector4 vector = sourcePixels[offsetX, offsetY].ToVector4().Expand();
+                            Vector4 vector = pixel.ToVector4().Expand();
                             vector -= shiftVector;
                             vector *= contrastVector;
                             vector += shiftVector;
-                                TPixel packed = default(TPixel);
+
-                                packed.PackFromVector4(vector.Compress());
+                            pixel.PackFromVector4(vector.Compress());
-                                sourcePixels[offsetX, offsetY] = packed;
                         }
                     });
         }
     }
 }
-}