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fix(impact): pass the IMPACT models their statistics flat and in itk-impact's order - #193

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fix/impact-mind-stats
Sep 17, 2026
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fix/impact-mind-stats

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@vboussot vboussot commented Sep 16, 2026

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Problem

ImpactFeatureModel.inputs built the intensity statistics as [[min, mean, max, std]]. The IMPACT TorchScript models read stats only when it holds exactly 4 values, and expect it flat, in itk-impact's order [min, max, mean, std] (itkImpactModelConfigurationDetail.h). Otherwise they compute the statistics from x themselves.

Read out of the shipped models (model.normalize.code):

model with 4 values otherwise
MIND (x - stats[0]) / (stats[1] - stats[0]) min/max of the tensor it is handed
TS MRI (M730/M850/M852) (x - stats[2]) / stats[3] mean/std of the tensor it is handed
SAM 2.1 same as MIND, then ImageNet mean/std min/max of the tensor it is handed
TS CT (M291), Anatomix ignore stats fixed buffers

Three bugs followed:

  • Crash with a single sample. The [1, 4] row also has numel() == 4, so MIND and TS took the branch that reads stats. stats[0] was then a 4-vector subtracted from the image, and MIND failed with size of tensor a (32) must match the size of tensor b (4). This broke every FireANTs + IMPACT/MIND run.
  • Wrong normalisation. Because the order was wrong, MIND divided by (mean - min) instead of (max - min), and TS MRI standardised around the max instead of the mean.
  • Batch-wide normalisation. A [B, 4] block is not 4 values either, so every sample of a batch was normalised by the batch's min/max or mean/std, which is another case's intensities. SAM is worse: its gate is stats.size(0) == 4, so a batch of exactly 4 passed it and took a whole row as the minimum.

impact-reg already had a fix: _ImpactCore.preprocessing flattened the row. It became dead code when the measures moved to ImpactFeatureModel.inputs. Nothing calls it any more, and the super().preprocessing it calls no longer exists.

Change

  • inputs takes one sample's attribute and returns itk-impact's flat order.
  • slice_losses scores one sample at a time, as itk-impact does and as _pca_project already did for the same reason. Same work in more kernels: +5 % (B=2) to +17 % (B=4) of the model's time, measured on an RTX PRO 5000.
  • The dead override is removed from impact-reg.
  • Two regression tests: the order, and each sample of a batch reading its own row.

Checked against the real MIND model, on a batch pairing a CT-scale volume with a [0, 1] one: the batch now scores 0.287980, exactly the mean of the two scored alone, where it scored 0.144727 before.

Behaviour change

A single sample used to crash before it could read the wrong order, so nothing that worked is changed there. A batch of B > 1 now scores differently: it used to be normalised batch-wide, it is now normalised per sample. Runs whose samples share an intensity scale barely move; a mixed batch moves a lot (2x above, deliberately extreme).

Summary by CodeRabbit

  • Bug Fixes

    • Corrected image statistics ordering to consistently report minimum, maximum, mean, and standard deviation.
    • Preserved batch-shaped statistics for multi-sample inputs while maintaining appropriate formatting for single-sample inputs.
    • Ensured batched scoring uses the corresponding statistics and masks for each sample and applicable slice.
    • Prevented preprocessing from unintentionally flattening singleton-batch statistics.
  • Tests

    • Added regression coverage for statistics ordering and batch dimensions.

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  • konfai/metric/measure/impact.py
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📝 Walkthrough

Walkthrough

The change corrects impact statistic ordering and single-sample shape handling. Batched scoring now processes each sample with its matching attributes and mask. Regression tests cover these behaviors. Fireants uses inherited preprocessing.

Changes

Impact statistics handling

Layer / File(s) Summary
Impact statistics and per-sample scoring
konfai/metric/measure/impact.py, tests/unit/test_measure.py
ImpactFeatureModel.inputs accepts one Attribute and emits flat statistics in [ImageMin, ImageMax, ImageMean, ImageStd] order. slice_losses processes each sample and applicable 2-D slice with matching output and target attributes and mask. Tests validate statistic ordering and batched scoring.
Inherited preprocessing integration
apps/impact_reg/impact_reg_konfai/models/fireants.py
Fireants no longer overrides _ImpactCore.preprocessing. Preprocessing follows IMPACTReg unchanged.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to 744b4

The updated scoring path preserves compatible per-sample statistics handling, with no actionable merge-blocking risk identified.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name Status Explanation Resolution
Docstring Coverage ⚠️ Warning Docstring coverage is 37.50% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 8 functions across 2 files. Write docstrings for the functions missing them to satisfy the coverage threshold.
✅ Passed checks (4 passed)
Check name Status Explanation
Linked Issues check ✅ Passed Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check ✅ Passed Check skipped because no linked issues were found for this pull request.
Title check ✅ Passed The title uses Conventional Commits format and clearly identifies the main change: passing IMPACT model statistics in flat itk-impact order.
Description check ✅ Passed The description clearly explains the problem, root cause, implementation, behavior change, performance impact, and regression testing. It does not use every template section, but it is sufficiently co…
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A rabbit checks each statistic in line
Min, max, mean, and std align
Each sample brings its matching pair
Masks and slices travel with care
Fireants follows the inherited trail
Tests raise a quiet victory tail

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perf facts (exit 0)

bench fact value expected verdict
predict differing_voxels_whole_vs_stream 0 == 0 holds
predict geometry_identical_whole_vs_stream 1 == 1 holds
transform max_abs_diff_konfai_vs_naive 1.19209e-07 <= 1e-06 holds
transform shape_equal_konfai_vs_naive 1 == 1 holds
transform attrs_equal_konfai_vs_naive 1 == 1 holds
transform sweep_peak_gib_b1 0.45 <= 1 holds
transform sweep_peak_gib_b8 2.64 <= 8 holds
[facts] 0 violation(s) over 7 fact(s)
times on this runner, reported only

benchmarks/perf on runnervmlun5p at 2026-09-17T20:47:27+0000

commit v1.8.5-7-g5cf3abc, no GPU, profile unavailable, load [0.83, 0.29, 0.11], OMP_NUM_THREADS=None

bench headline file
startup import konfai 0.06 s / konfai.trainer 1.492 s (339 MB); konfai --help 0.103 s 20260917-204753-5cf3abca-startup.json
predict prediction whole 6.158 s (loop 3.1: fetch 0.2 + forward 2.0) streamed 5.869 s (loop 2.9)
transform 2 GiB: KonfAI 4.706 s / 0.814 GiB at 1 GiB budget, 4.649 s at 8 GiB naive 6.72 s / 0.234 GiB

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Actionable comments posted: 1

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Inline comments:
In `@konfai/metric/measure/impact.py`:
- Around line 221-230: Update ImpactFeatureModel.inputs and its TorchScript/MIND
consumers so batched attributes preserve each sample’s (B, 4)
ImageMin/ImageMax/ImageMean/ImageStd statistics during normalization; do not
trigger batch-wide fallback for B > 1. Ensure single-sample behavior remains
compatible and add a regression test covering batched normalization.

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📒 Files selected for processing (3)
  • apps/impact_reg/impact_reg_konfai/models/fireants.py
  • konfai/metric/measure/impact.py
  • tests/unit/test_measure.py
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  • apps/impact_reg/impact_reg_konfai/models/fireants.py

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Comment thread konfai/metric/measure/impact.py Outdated
…impact's order

ImpactFeatureModel.inputs built stats as [[min, mean, max, std]]. The TorchScript models read
them only when stats.numel() == 4, as a flat [min, max, mean, std] (the itk-impact contract):

- a single sample gave a [1, 4] row, numel 4 too, so stats[0] was a 4-vector subtracted from the
  image and MIND failed with "size of tensor a (32) must match the size of tensor b (4)";
- min, mean, max, std made MIND and SAM divide by (mean - min) and TS standardise around the max.

A batch failed the same test the other way: a [B, 4] block is not 4 values either, so every sample
was normalized by the batch's own min/max (MIND) or mean/std (the MRI TS models), which is another
case's intensities. slice_losses now scores one sample at a time, as itk-impact does and as
_pca_project already did, so a batch scores exactly as its samples scored alone. It is the same work
in more kernels: measured 5 % (B=2) to 17 % (B=4) of the model's time on an RTX PRO 5000.

impact-reg's _ImpactCore.preprocessing flattened the row, but nothing has called preprocessing
since the measures moved to ImpactFeatureModel.inputs, and its super() no longer exists: removed.
@vboussot
vboussot force-pushed the fix/impact-mind-stats branch from f0fad4c to 744b4e6 Compare September 17, 2026 20:45
@vboussot
vboussot merged commit 113fe84 into main Sep 17, 2026
26 checks passed
@vboussot
vboussot deleted the fix/impact-mind-stats branch September 17, 2026 21:08
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