fix

tests/test_processing.py

@@ -454,6 +454,27 @@ class ProcessingTests(unittest.TestCase):
         self.assertIsNone(dec_axis)
         self.assertEqual(dec_data.shape, (3, 4))
 
+    def test_bscan_background_profile_tracks_decimated_rows(self):
+        rows = (FFT_LEN // 2) + 1
+        axis = np.linspace(0.0, 10.0, rows, dtype=np.float64)
+        background = np.linspace(1.0, 2.0, rows, dtype=np.float32)
+        residual = np.linspace(0.1, 0.4, rows, dtype=np.float32)
+        data = background[:, None] + residual[:, None]
+
+        dec_axis, dec_data, row_idx = decimate_bscan_rows_for_display(
+            axis,
+            data,
+            max_points=512,
+            return_indices=True,
+        )
+        dec_background = background[row_idx]
+        subtracted = subtract_fft_background(dec_data, dec_background)
+
+        self.assertEqual(dec_axis.shape, (512,))
+        self.assertEqual(dec_data.shape, (512, 1))
+        self.assertEqual(row_idx.shape, (512,))
+        self.assertTrue(np.allclose(subtracted[:, 0], residual[row_idx], atol=1e-6))
+
     def test_update_expected_sweep_width_initializes_from_first_valid_sweep(self):
         self.assertEqual(update_expected_sweep_width(0, 411), 411)