Hironabe333/tflite-score-thresholding-metadata-authority-poc

TFLite ScoreThresholdingOptions Metadata Authority — PoC

Summary

This repository demonstrates that the MediaPipe Task Library ImageClassifier reads and applies ScoreThresholdingOptions.global_score_threshold from a model's embedded TFLITE_METADATA FlatBuffer as a fallback score filter during post-inference processing, without user visibility or warning.

An adversarially crafted model with global_score_threshold = 1e9 embedded in outputTensorMetadata[0].process_units[] causes the classifier to return zero categories silently — even though the model graph, weights, and inference scores are unchanged.

An explicit API score_threshold parameter overrides the metadata value and restores output, confirming that metadata acts as the fallback authority when the API caller does not set a threshold explicitly.

Affected consumer: MediaPipe Task Library ImageClassifier
Not affected: Raw TFLite Interpreter (does not apply ScoreThresholdingOptions)
Root: TensorMetadata.process_units[].ScoreThresholdingOptions.global_score_threshold
Runtime stage: Post-inference score filtering (output side)
Authority type: Fallback — API score_threshold overrides when explicitly set

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Affected Consumer

The MediaPipe Task Library ImageClassifier automatically reads ScoreThresholdingOptions from outputTensorMetadata[0].process_units[] in the model's TFLITE_METADATA FlatBuffer. This value is used as the default score threshold when the API caller does not provide one:

import mediapipe as mp
from mediapipe.tasks import python
from mediapipe.tasks.python.vision import ImageClassifier, ImageClassifierOptions

opts = ImageClassifierOptions(
    base_options = python.BaseOptions(model_asset_path="model.tflite"),
    max_results = 10
    # No score_threshold set — uses metadata fallback
)

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Files

File	Description
reproduce_tflite_score_thresholding_suppression.py	Reproduction script
inspect_score_thresholding_hash_matrix.py	Hash matrix inspection script
*.pklM	Model files
requirements.txt	Python dependencies
SHA256SUMS.txt	Checksums