Fix the matplotlib backend for qc plotting#797
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m-reuter merged 2 commits intoDeep-MI:devfrom Mar 7, 2026
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- Add `noop_context` and `backend` context manager for safe matplotlib backend switching FastSurferCNN/utils/__init__.py
- Use `backend('agg')` context to fix --qc_snaps failure when qt unavailable in HypVINN/utils/visualization_utils.py, CorpusCallosum/shape/endpoint_heuristic.py, CorpusCallosum/shape/postprocessing.py and CorpusCallosum/utils/visualization.py
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Pull request overview
This PR aims to make QC snapshot/plot generation more robust in headless environments by introducing a Matplotlib-backend context manager and using it in HypVINN and CorpusCallosum plotting paths (instead of relying on whatever the default GUI backend is).
Changes:
- Add
FastSurferCNN.utils.plotting.backend()context manager to temporarily switch Matplotlib backends. - Use the backend context for HypVINN QC snapshot generation and CorpusCallosum plotting/debug plotting.
- Update HypVINN
run_prediction.pyexecution flow (thread executor usage + improved QC future error reporting).
Reviewed changes
Copilot reviewed 9 out of 9 changed files in this pull request and generated 5 comments.
Show a summary per file
| File | Description |
|---|---|
| HypVINN/utils/visualization_utils.py | Wrap QC snapshot figure creation/saving in a forced agg backend context; refactor cropping logic. |
| HypVINN/run_prediction.py | Switch executor selection logic and improve QC snapshot async error handling/logging. |
| FastSurferCNN/utils/plotting.py | New backend-switching context manager utility. |
| FastSurferCNN/utils/init.py | Export new noop_context utility. |
| CorpusCallosum/utils/visualization.py | Use backend context (or no-op) for plotting depending on whether saving is requested. |
| CorpusCallosum/shape/postprocessing.py | Replace manual backend switching with backend context for interactive debug plots. |
| CorpusCallosum/shape/metrics.py | Replace manual backend switching with backend context for interactive debug plots. |
| CorpusCallosum/shape/endpoint_heuristic.py | Replace manual backend switching with backend context for interactive debug plots + minor plotting arg tweaks. |
| CorpusCallosum/segmentation/segmentation_postprocessing.py | Replace manual backend switching with backend context for interactive debug plots. |
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…and use the global executor instances instead of local instances - Only import matplotlib.pyplot after backend context switches to avoid unavailable backend errors - Log warnings if qc image generation failed in HypVINN Clean up formatting
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HypVINN creates qc snapshots, if the
--qc__snapsfalg is passed, but this uses the "default" backend of matplotlib.So qc_snapshot generation fails, when the default backend is not available, e.g. default qtagg is not available because qt is not installed/available.
To resolve, we force the add matplotlib backend with a context manager.
The contextmanager solution is also propagated into the CorpusCallosum module, where a similar problem was addressed with manual backend switches.