Research-0111 — DISTS-Sq Extractor Implementation Notes¶

Context¶

ADR-0236 designed dists_sq as the DISTS companion to the shipped LPIPS full-reference extractor. The stale docs still marked the surface as a stub: no C extractor, no model registry entry, no placeholder ONNX, and no smoke test existed.

Implementation Shape¶

The extractor follows the existing LPIPS host pattern instead of introducing a second preprocessing path:

• Convert 8-bit YUV 4:2:0 / 4:2:2 / 4:4:4 frames to RGB.
• Convert RGB planes to ImageNet-normalised float32 NCHW tensors.
• Bind named ONNX inputs ref and dist.
• Read scalar output score and publish it as dists_sq.

The smoke checkpoint at model/tiny/dists_sq.onnx is intentionally tiny: Sub -> Mul -> ReduceMean. It locks the ABI and exercises named two-input binding without claiming production DISTS quality.

Follow-Up Boundary¶

T7-DISTS is closed by the extractor surface. T7-DISTS-followup remains open for real upstream-derived DISTS-compatible weights, representative-score validation, and any threshold guidance needed once the output matches the published metric rather than the smoke graph.

Verification¶

.venv/bin/python ai/scripts/gen_dists_sq_placeholder_onnx.py --check
meson test -C build-dists test_dists

References¶

• ADR-0236
• Research-0043
• req: user pointed at the DISTS extractor (stub) docs page and asked to do that gap next.