Higher threshold for LomographTest

tests/ImageSharp.Tests/Processing/Processors/Filters/LomographTest.cs

@@ -7,6 +7,8 @@ using Xunit;
 
 namespace SixLabors.ImageSharp.Tests.Processing.Processors.Filters
 {
+    using SixLabors.ImageSharp.Tests.TestUtilities.ImageComparison;
+
     [GroupOutput("Filters")]
     public class LomographTest
     {
@@ -15,7 +17,7 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Filters
         public void ApplyLomographFilter<TPixel>(TestImageProvider<TPixel> provider)
             where TPixel : struct, IPixel<TPixel>
         {
-            provider.RunValidatingProcessorTest(x => x.Lomograph());
+            provider.RunValidatingProcessorTest(x => x.Lomograph(), comparer: ImageComparer.Tolerant(-2));
         }
     }
 }

tests/ImageSharp.Tests/TestUtilities/ImageComparison/ImageComparer.cs

@@ -18,7 +18,7 @@ namespace SixLabors.ImageSharp.Tests.TestUtilities.ImageComparison
         /// <summary>
         /// Returns an instance of <see cref="TolerantImageComparer"/>.
         /// Individual manhattan pixel difference is only added to total image difference when the individual difference is over 'perPixelManhattanThreshold'.
-        /// Negative value for 'imageThreshold' indicates default threshold (see <see cref="TolerantImageComparer.DefaultImageThreshold"/>).
+        /// Negative value for 'imageThreshold' indicates multiplier to be applied to the default threshold (see <see cref="TolerantImageComparer.DefaultImageThreshold"/>).
         /// </summary>
         public static ImageComparer Tolerant(
             float imageThreshold = -1,

tests/ImageSharp.Tests/TestUtilities/ImageComparison/TolerantImageComparer.cs

@@ -15,14 +15,14 @@
         public static readonly float DefaultImageThreshold = GetDefaultImageThreshold();
 
         /// <summary>
-        /// Negative value for 'imageThreshold' indicates default threshold (see <see cref="DefaultImageThreshold"/>).
+        /// Negative value for 'imageThreshold' indicates a multiplier to be applied to the default threshold (see <see cref="DefaultImageThreshold"/>).
         /// Individual manhattan pixel difference is only added to total image difference when the individual difference is over 'perPixelManhattanThreshold'.
         /// </summary>
         public TolerantImageComparer(float imageThreshold, int perPixelManhattanThreshold = 0)
         {
             if (imageThreshold < 0)
             {
-                imageThreshold = DefaultImageThreshold;
+                imageThreshold *= -DefaultImageThreshold;
             }
 
             this.ImageThreshold = imageThreshold;

tests/ImageSharp.Tests/TestUtilities/Tests/ImageComparerTests.cs

@@ -23,6 +23,19 @@ namespace SixLabors.ImageSharp.Tests
 
         private ITestOutputHelper Output { get; }
 
+        [Fact]
+        public void TolerantImageComparer_NegativeThresholdIsMultiplierForDefault()
+        {
+            var c1 = (TolerantImageComparer)ImageComparer.Tolerant();
+            var c2 = (TolerantImageComparer)ImageComparer.Tolerant(-2);
+            var c3 = (TolerantImageComparer)ImageComparer.Tolerant(-42);
+
+            Assert.True(c1.ImageThreshold > 0);
+            Assert.Equal(TolerantImageComparer.DefaultImageThreshold, c1.ImageThreshold);
+            Assert.Equal(c1.ImageThreshold * 2, c2.ImageThreshold);
+            Assert.Equal(c1.ImageThreshold * 42, c3.ImageThreshold);
+        }
+
         [Theory]
         [WithTestPatternImages(100,100,PixelTypes.Rgba32, 0.0001f, 1)]
         [WithTestPatternImages(100, 100, PixelTypes.Rgba32, 0, 0)]