Third Edition

This release is the Portable Network Graphics (PNG) Specification (Third Edition)
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W3C Recommendation 24 June 2025

It can be found at https://www.w3.org/TR/2025/REC-png-3-20250624/

2nd Edition (2003)

This release is the Portable Network Graphics (PNG) Specification (Second Edition)
Information technology — Computer graphics and image processing — Portable Network Graphics (PNG): Functional specification. ISO/IEC 15948:2003 (E)
W3C Recommendation 10 November 2003

It can be found at https://www.w3.org/TR/2003/REC-PNG-20031110/