Implement grouping score, customizable export weights, and fix color selection bug

tests/test_image_processor.py

@@ -19,7 +19,8 @@ def test_stats_summary():
             return key
         return f"{kwargs['with_pct']:.1f} {kwargs['without_pct']:.1f} {kwargs['excluded_pct']:.1f}"
 
-    res = s.summary(mock_t)
+    weights = {"match_all": 30, "match_keep": 50, "brightness": 10, "grouping": 10}
+    res = s.summary(mock_t, weights)
     # with_pct: 40/80 = 50.0
     # without_pct: 50/100 = 50.0
     # excluded_pct: 20/100 = 20.0
@@ -27,7 +28,8 @@ def test_stats_summary():
 
 def test_stats_empty():
     s = Stats()
-    assert s.summary(lambda k, **kw: "Empty") == "Empty"
+    weights = {"match_all": 30, "match_keep": 50, "brightness": 10, "grouping": 10}
+    assert s.summary(lambda k, **kw: "Empty", weights) == "Empty"
 
 
 def test_rgb_to_hsv_numpy():
@@ -121,3 +123,35 @@ def test_coordinate_scaling():
     assert s_large.total_all == 1000000
     assert s_large.total_keep == 500000
     assert s_large.total_excl == 500000
+
+def test_calculate_grouping_score():
+    proc = QtImageProcessor()
+    
+    # 1. Empty mask
+    mask_empty = np.zeros((20, 20), dtype=bool)
+    assert proc._calculate_grouping_score(mask_empty) == 0.0
+    
+    # 2. Single mask pixel (0 neighbors)
+    mask_single = np.zeros((20, 20), dtype=bool)
+    mask_single[10, 10] = True
+    assert proc._calculate_grouping_score(mask_single) == 0.0
+    
+    # 3. 2x2 block
+    # each pixel in 2x2 has 3 neighbors in 3x3, 3 neighbors in 5x5, 3 neighbors in 9x9.
+    # score = ((3/80)^2) * 100
+    expected_2x2 = ((3/80.0)**2) * 100.0
+    mask_block = np.zeros((20, 20), dtype=bool)
+    mask_block[10:12, 10:12] = True
+    assert pytest.approx(proc._calculate_grouping_score(mask_block)) == expected_2x2
+    
+    # 4. 9x9 block
+    # center pixel has 80 neighbors (100% density).
+    # many pixels have high density.
+    mask_9x9 = np.zeros((20, 20), dtype=bool)
+    mask_9x9[5:14, 5:14] = True
+    res_9x9 = proc._calculate_grouping_score(mask_9x9)
+    assert res_9x9 > expected_2x2
+    # For a 9x9 block, the center pixel is 100%. Boundary pixels are less.
+    # 1 center pixel = 80/80 = 1.0. 
+    # Overall it should be a healthy percentage.
+    assert res_9x9 > 10.0 # significant grouping