Add pluggable image-comparison strategies with auto-selection, benchmarking, and test harness

.github/workflows/ci.yml

@@ -19,13 +19,16 @@ jobs:
       - name: Setup .NET
         uses: actions/setup-dotnet@v4
         with:
-          dotnet-version: "8.0.x"
+          dotnet-version: "10.0.x"
 
       - name: Restore dependencies
         run: dotnet restore
 
       - name: Build
         run: dotnet build --no-restore --configuration Release
 
+      - name: Run tests
+        run: dotnet run --no-build --configuration Release --project ImageComparator.Tests/ImageComparator.Tests.csproj
+
       - name: Publish (self-contained)
         run: dotnet publish --no-build --configuration Release --output publish

ImageComparator.Tests/ImageComparator.Tests.csproj

@@ -0,0 +1,14 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <ItemGroup>
+    <ProjectReference Include="..\ImageComparator\ImageComparator.csproj" />
+  </ItemGroup>
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

ImageComparator.Tests/Program.cs

@@ -0,0 +1,121 @@
+namespace ImageComparator.Tests;
+
+using System.Drawing;
+using System.Runtime.Versioning;
+using ImageComparator;
+
+[SupportedOSPlatform("windows")]
+internal static class Program
+{
+    private static int Main()
+    {
+        if (!OperatingSystem.IsWindows())
+        {
+            Console.WriteLine("Tests skipped: System.Drawing comparisons are Windows-only.");
+            return 0;
+        }
+
+        var tests = new (string Name, Action Execute)[]
+        {
+            ("Strategies rank identical above different", StrategiesRankIdenticalAboveDifferent),
+            ("Auto strategy picks dHash for very large images", AutoStrategyPicksDifferenceHashForLargeImages),
+            ("Benchmark returns concrete strategies", BenchmarkReturnsConcreteStrategies),
+        };
+
+        var failures = new List<string>();
+
+        foreach (var (name, execute) in tests)
+        {
+            try
+            {
+                execute();
+                Console.WriteLine($"PASS: {name}");
+            }
+            catch (Exception ex)
+            {
+                failures.Add($"{name}: {ex.Message}");
+                Console.WriteLine($"FAIL: {name}");
+            }
+        }
+
+        if (failures.Count == 0)
+        {
+            return 0;
+        }
+
+        Console.WriteLine();
+        Console.WriteLine("Failures:");
+        foreach (var failure in failures)
+        {
+            Console.WriteLine($"- {failure}");
+        }
+
+        return 1;
+    }
+
+    private static void StrategiesRankIdenticalAboveDifferent()
+    {
+        using var imageA = CreateSolidBitmap(Color.Red);
+        using var imageB = CreateSolidBitmap(Color.Red);
+        using var imageC = CreateSolidBitmap(Color.Blue);
+
+        var strategies = new[]
+        {
+            ComparisonStrategy.LegacyDominantChannel,
+            ComparisonStrategy.MeanAbsoluteDifference,
+            ComparisonStrategy.DifferenceHash,
+        };
+
+        foreach (var strategy in strategies)
+        {
+            var comparer = new BitmapCompare(strategy);
+            var sameSimilarity = comparer.GetSimilarity(imageA, imageB);
+            var differentSimilarity = comparer.GetSimilarity(imageA, imageC);
+
+            AssertTrue(
+                sameSimilarity > differentSimilarity,
+                $"{strategy} expected sameSimilarity > differentSimilarity but was {sameSimilarity:F4} <= {differentSimilarity:F4}");
+        }
+    }
+
+    private static void AutoStrategyPicksDifferenceHashForLargeImages()
+    {
+        using var imageA = CreateSolidBitmap(Color.Green, width: 2400, height: 1600);
+        using var imageB = CreateSolidBitmap(Color.Green, width: 2400, height: 1600);
+        var comparer = new BitmapCompare(ComparisonStrategy.Auto);
+
+        _ = comparer.GetSimilarity(imageA, imageB);
+
+        AssertTrue(
+            comparer.LastStrategyUsed == ComparisonStrategy.DifferenceHash,
+            $"Expected {ComparisonStrategy.DifferenceHash} but got {comparer.LastStrategyUsed}");
+    }
+
+    private static void BenchmarkReturnsConcreteStrategies()
+    {
+        using var imageA = CreateSolidBitmap(Color.White);
+        using var imageB = CreateSolidBitmap(Color.Black);
+        var results = ComparisonBenchmark.Run(imageA, imageB, iterations: 3);
+
+        AssertTrue(results.Count == 3, $"Expected 3 benchmark rows, got {results.Count}");
+        AssertTrue(
+            results.All(result => result.Strategy != ComparisonStrategy.Auto),
+            "Benchmark should return only concrete strategies.");
+    }
+
+    private static Bitmap CreateSolidBitmap(Color color, int width = 64, int height = 64)
+    {
+        var bitmap = new Bitmap(width, height);
+        using var graphics = Graphics.FromImage(bitmap);
+        graphics.Clear(color);
+        return bitmap;
+    }
+
+    private static void AssertTrue(bool condition, string message)
+    {
+        if (!condition)
+        {
+            throw new InvalidOperationException(message);
+        }
+    }
+}

ImageComparator.sln

@@ -1,20 +1,46 @@
-
+
 Microsoft Visual Studio Solution File, Format Version 12.00
 # Visual Studio Version 17
 VisualStudioVersion = 17.0.31903.59
 MinimumVisualStudioVersion = 10.0.40219.1
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "ImageComparator", "ImageComparator\ImageComparator.csproj", "{04C06855-4D15-4E39-B460-257E4CC0B65A}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "ImageComparator.Tests", "ImageComparator.Tests\ImageComparator.Tests.csproj", "{81EF9DFF-D736-4530-B67E-F942E7DBB5C9}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
+		Debug|x64 = Debug|x64
+		Debug|x86 = Debug|x86
 		Release|Any CPU = Release|Any CPU
+		Release|x64 = Release|x64
+		Release|x86 = Release|x86
 	EndGlobalSection
 	GlobalSection(ProjectConfigurationPlatforms) = postSolution
 		{04C06855-4D15-4E39-B460-257E4CC0B65A}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
 		{04C06855-4D15-4E39-B460-257E4CC0B65A}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{04C06855-4D15-4E39-B460-257E4CC0B65A}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{04C06855-4D15-4E39-B460-257E4CC0B65A}.Debug|x64.Build.0 = Debug|Any CPU
+		{04C06855-4D15-4E39-B460-257E4CC0B65A}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{04C06855-4D15-4E39-B460-257E4CC0B65A}.Debug|x86.Build.0 = Debug|Any CPU
 		{04C06855-4D15-4E39-B460-257E4CC0B65A}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{04C06855-4D15-4E39-B460-257E4CC0B65A}.Release|Any CPU.Build.0 = Release|Any CPU
+		{04C06855-4D15-4E39-B460-257E4CC0B65A}.Release|x64.ActiveCfg = Release|Any CPU
+		{04C06855-4D15-4E39-B460-257E4CC0B65A}.Release|x64.Build.0 = Release|Any CPU
+		{04C06855-4D15-4E39-B460-257E4CC0B65A}.Release|x86.ActiveCfg = Release|Any CPU
+		{04C06855-4D15-4E39-B460-257E4CC0B65A}.Release|x86.Build.0 = Release|Any CPU
+		{81EF9DFF-D736-4530-B67E-F942E7DBB5C9}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{81EF9DFF-D736-4530-B67E-F942E7DBB5C9}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{81EF9DFF-D736-4530-B67E-F942E7DBB5C9}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{81EF9DFF-D736-4530-B67E-F942E7DBB5C9}.Debug|x64.Build.0 = Debug|Any CPU
+		{81EF9DFF-D736-4530-B67E-F942E7DBB5C9}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{81EF9DFF-D736-4530-B67E-F942E7DBB5C9}.Debug|x86.Build.0 = Debug|Any CPU
+		{81EF9DFF-D736-4530-B67E-F942E7DBB5C9}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{81EF9DFF-D736-4530-B67E-F942E7DBB5C9}.Release|Any CPU.Build.0 = Release|Any CPU
+		{81EF9DFF-D736-4530-B67E-F942E7DBB5C9}.Release|x64.ActiveCfg = Release|Any CPU
+		{81EF9DFF-D736-4530-B67E-F942E7DBB5C9}.Release|x64.Build.0 = Release|Any CPU
+		{81EF9DFF-D736-4530-B67E-F942E7DBB5C9}.Release|x86.ActiveCfg = Release|Any CPU
+		{81EF9DFF-D736-4530-B67E-F942E7DBB5C9}.Release|x86.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE