Original PickImageColors source-file lab, 2026-10-25.
Does renaming a JPEG to PNG restore the original colors?
Run: python reproduce.py --case renaming-jpeg-to-png --out rerun
Dependency: Pillow. Recorded runtime: Python 3.12.14, Pillow 12.3.0, libwebp 1.6.0.
Measurements are local source-file computations, not browser observations. Library-dependent compression sizes and quantizer choices may change with runtime.
The changed-pixel count belongs to this synthetic image and this recorded encoder/decoder runtime. It is not a quality score for every JPEG. We did not test browser MIME handling or claim that an upload interface accepts misleading extensions.
