Why Identical Pixels Can Produce Different PNG File Hashes
A narrow note on choosing the correct comparison layer for benchmark output.
Note identity
- Note ID
- FRN-2026-001
- Schema
- FARPY-RESEARCH-NOTE-V1
- Publication date
- 2026-07-21
- Revision
- 1
- Source report
- FRS-2026-001
Question
Can two PNG files represent identical decoded pixels while having different complete-file hashes?
Finding
Yes, in the documented Octane experiment. The decoded pixel payloads matched across the measured outputs, while the complete PNG file hashes differed. The canonical evidence attributed the container-level byte differences to changing PNG metadata.
Evidence
FRS-2026-001 records two separate checks: decoded pixel comparison and complete-file hash comparison. The pixel comparison passed. The complete-file hashes did not match. Inspection tied the byte-level difference to PNG metadata rather than a difference in the decoded pixels.
Interpretation
Pixel equivalence and file-byte equivalence are different properties. A full-file SHA-256 hash answers whether every byte in the PNG container is identical. A decoded-pixel comparison answers whether the raster payload presented by the decoder is identical. Benchmark validation should select the semantic layer that matches the claim being tested. If the claim concerns rendered pixels, comparing only container bytes can reject outputs whose pixel payloads match. If the claim concerns exact artifact reproduction, a complete-file hash remains the relevant check.
Limitation
This finding is limited to the recorded contract, outputs, and evidence in FRS-2026-001. It does not prove that every PNG metadata difference is harmless. Metadata may itself be required evidence, and any unexplained difference still warrants inspection. This note does not establish a verified Octane performance result.
Citation
Farpy Research Station. "Why Identical Pixels Can Produce Different PNG File Hashes." FRN-2026-001, revision 1, 2026.
Related full report
FRS-2026-001: Octane Pixel Determinism Versus Runtime Instability
Canonical URL: https://farpy.com/labs/research/frn-2026-001-identical-pixels-different-png-hashes