W3C: REC-png.html

PNG (Portable Network Graphics) Specification

Version 1.1

W3C Recommendation draft-02-Nov-1998

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1. Introduction

The Portable Network Graphics (PNG) format provides a portable, legally unencumbered, well-compressed, well-specified standard for lossless bitmapped image files.

Although the initial motivation for developing PNG was to replace GIF (Compuserve's Graphics Interchange Format), the design provides some useful new features not available in GIF, with minimal cost to developers.

GIF features retained in PNG include:

Important new features of PNG, not available in GIF, include:

PNG is designed to be:

The main part of this specification gives the definition of the file format and recommendations for encoder and decoder behavior. An appendix gives the rationale for many design decisions. Although the rationale is not part of the formal specification, reading it can help implementors understand the design. Cross-references in the main text point to relevant parts of the rationale. Additional appendixes, also not part of the formal specification, provide tutorials on gamma and color theory as well as other supporting material.

The words "must", "required", "should", "recommended", "may", and "optional" in this document are to be interpreted as described in [RFC-2119], which is consistent with their plain English meanings. The word "can" carries the same force as "may".

See Rationale: Why a new file format?, Why these features?, Why not these features?, Why not use format X?.


PNG is pronounced "ping".

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