TASK 51 slice 2: Blur — background at 1/4 res, 3 separable box passes (~gaussian, radius by strength), mask-blended; person untouched; Remove gains strength = edge feather; mask computed once, rendered per effect (Unit: bg blur)

ytLive.Tests/BackgroundEffectEngineTests.cs

@@ -99,6 +99,54 @@ public class BackgroundEffectEngineTests
         Assert.InRange(100.0 * person / total, 45, 60); // reference: 52.5% person
     }
 
+    /// <summary>Slice 2 integration test: Blur keeps the person pixel-for-pixel and smooths the
+    /// background — a 1px black/white checkerboard behind the "person" comes back as mid-tones,
+    /// opaque, same size.</summary>
+    [Fact]
+    public void Blur_keeps_the_person_sharp_and_smooths_the_background()
+    {
+        const int w = 64, h = 32;
+        var pixels = new byte[w * h * 4];
+        for (var y = 0; y < h; y++)
+        for (var x = 0; x < w; x++)
+        {
+            var p = (y * w + x) * 4;
+            if (x < w / 2)
+            {
+                pixels[p] = 100; pixels[p + 1] = 150; pixels[p + 2] = 200;
+            }
+            else
+            {
+                var v = (byte)(((x + y) & 1) == 0 ? 0 : 255);
+                pixels[p] = v; pixels[p + 1] = v; pixels[p + 2] = v;
+            }
+            pixels[p + 3] = 255;
+        }
+        var frame = new VideoFrame(w, h, pixels) { IsOpaque = true };
+        var mask = new SegmentationMask(4, 2, new[] { 1f, 1f, 0f, 0f, 1f, 1f, 0f, 0f });
+        var processor = new BackgroundEffectProcessor(new FakeSegmenter(mask));
+
+        var result = processor.Apply(frame, BackgroundEffect.Blur);
+
+        Assert.NotSame(frame, result);
+        Assert.True(result.IsOpaque);
+        Assert.Equal(w, result.Width);
+        Assert.Equal(h, result.Height);
+        for (var y = 0; y < h; y++)
+        {
+            for (var x = 0; x < 24; x++)                 // person: untouched
+                for (var c = 0; c < 4; c++)
+                    Assert.Equal(pixels[(y * w + x) * 4 + c], result.BgraPixels[(y * w + x) * 4 + c]);
+            for (var x = 44; x < w; x++)                 // background: checkerboard smoothed away
+            {
+                var p = (y * w + x) * 4;
+                for (var c = 0; c < 3; c++)
+                    Assert.InRange(result.BgraPixels[p + c], (byte)30, (byte)225);
+                Assert.Equal(255, result.BgraPixels[p + 3]);
+            }
+        }
+    }
+
     private static int Alpha(VideoFrame f, int x, int y) => f.BgraPixels[(y * f.Width + x) * 4 + 3];
 
     private static string Fixture(string name) => Path.Combine(AppContext.BaseDirectory, "Fixtures", name);