Correct H&E stain ordering heuristic in ExtractHEStains #8551
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The previous heuristic incorrectly assumed hematoxylin has higher red channel values than eosin, when the opposite is typically true. Replace red-channel-only comparison with more robust red-blue ratio comparison to better distinguish hematoxylin from eosin stains based on their spectral properties. - Hematoxylin (nuclear, blue): lower red/blue ratio -> first column - Eosin (cytoplasm, pink): higher red/blue ratio -> second column Update tests to reflect corrected stain ordering. Documented behaviour (first column = H, second = E) now matches the actual output. Signed-off-by: Iyassou Shimels <[email protected]>
WalkthroughThe HE stain ordering logic in monai/apps/pathology/transforms/stain/array.py now uses a red-to-blue ratio comparison between two candidate vectors (v_min and v_max), with an epsilon to avoid division by zero. If v_min’s ratio is lower than v_max’s, the order is kept (hematoxylin first); otherwise, vectors are swapped. Comments were added to explain the rationale. Corresponding tests in tests/apps/pathology/transforms/test_pathology_he_stain.py and test_pathology_he_stain_dict.py were updated to reflect the swapped stain column orientation and resulting normalized image values. No public API signatures changed. Estimated code review effort🎯 2 (Simple) | ⏱️ ~12 minutes ✨ Finishing Touches
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🧹 Nitpick comments (1)
monai/apps/pathology/transforms/stain/array.py (1)
88-96: Use ASCII name for epsilon and make the ratio robust to sign/near-zero blue; stabilize ties.Avoid Unicode identifiers, and guard against negative/near-zero denominators and noisy ties. This reduces mis-ordering under sign flips and tiny B.
- # Hematoxylin: high blue, lower red (low R/B ratio) - # Eosin: high red, lower blue (high R/B ratio) - ε = np.finfo(np.float32).eps - v_min_rb_ratio = v_min[0, 0] / (v_min[2, 0] + ε) - v_max_rb_ratio = v_max[0, 0] / (v_max[2, 0] + ε) - if v_min_rb_ratio < v_max_rb_ratio: + # Hematoxylin: high blue, lower red (low |R|/|B| ratio) + # Eosin: high red, lower blue (high |R|/|B| ratio) + eps = np.finfo(np.float32).eps + v_min_rb_ratio = np.abs(v_min[0, 0]) / (np.abs(v_min[2, 0]) + eps) + v_max_rb_ratio = np.abs(v_max[0, 0]) / (np.abs(v_max[2, 0]) + eps) + # keep order on ties for determinism + if v_min_rb_ratio <= v_max_rb_ratio: he = np.array((v_min[:, 0], v_max[:, 0]), dtype=np.float32).T else: he = np.array((v_max[:, 0], v_min[:, 0]), dtype=np.float32).T
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monai/apps/pathology/transforms/stain/array.py(1 hunks)tests/apps/pathology/transforms/test_pathology_he_stain.py(4 hunks)tests/apps/pathology/transforms/test_pathology_he_stain_dict.py(4 hunks)
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🔇 Additional comments (7)
tests/apps/pathology/transforms/test_pathology_he_stain_dict.py (3)
42-46: Expected stain matrix update matches the new H/E ordering heuristic.Numbers reflect lower |R|/|B| for H (first col). Good.
61-66: Normalized image expectation updated consistently with swapped columns.Looks correct given the new he ordering.
201-214: Docstring aligns with the new derivation and values.Narrative and matrices are consistent.
tests/apps/pathology/transforms/test_pathology_he_stain.py (4)
48-52: Expected stain matrix reflects H first (lower |R|/|B|).Matches the revised heuristic.
67-72: Normalized image expectation updated for the new column order.Consistent with extraction change.
136-139: Docstring example adjusted to the new ordering.Values and explanation are coherent.
207-219: Case 4 docstring and matrices updated correctly.Concentration reordering and final image values track the new H/E order.
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Hi @bhashemian would you be able to review this change or suggest who might be better placed? Thanks! |
Description
I noticed when attempting to extract the hematoxylin stain from an H&E stained image that the previous heuristic for ordering hematoxylin first and eosin second incorrectly assumed hematoxylin has a higher red channel value, when the opposite is typically true. I've corrected this and implemented a more robust heuristic that compares red-blue ratios instead, since:
I've updated the tests to reflect the corrected stain ordering, and the output now accurately reflects the documented behaviour (first column hematoxylin, second eosin).
Types of changes
./runtests.sh -f -u --net --coverage../runtests.sh --quick --unittests --disttests.