PNG (Portable Network Graphics) Specification, Version 1.1

17. Appendix: Revision History

(This appendix is not part of the formal PNG specification.)

The PNG format has been frozen since the Ninth Draft of 7 March 1995, and all future changes are intended to be backward compatible. The revisions since the Ninth Draft are simply clarifications, improvements in presentation, additions of supporting material, and specifications for additional chunks.

On 1 October 1996, the PNG 1.0 specification was approved as a W3C (World Wide Web Consortium) Recommendation.

In January 1997 it was published as RFC-2083 (informational) with technical content identical to that of the W3C Recommendation.

In October 1998, the PNG 1.1 specification was approved by the PNG Development Group.

Changes since version 1.0

(W3C Recommendation 01-October-1996, RFC 2083 January 1997)

Note: These changes have been approved by the PNG Development Group, but not by any standards body.

• Redefined gAMA to be in terms of the desired display output rather than the original scene, and revised all discussions of gamma and references to gamma accordingly

• Added the iCCP, sPLT, and sRGB chunks

• Extended the scope of the 31-bit limit on chunk lengths and image dimensions to apply to all four-byte unsigned integers, and disallowed the value -231 in four-byte signed integers

• Mentioned the possibility of dithering the alpha channel when converting it to binary transparency

• Clarified that zlib window sizes smaller than 32K are valid

• Updated the PNG web site URL and authors' email addresses

• Editing and reformatting

Changes since the Tenth Draft of 5 May 1995

• Clarified meaning of a suggested-palette PLTE chunk in a truecolor image that uses transparency

• Clarified exact semantics of sBIT and allowed sample depth scaling procedures

• Clarified status of spaces in tEXt chunk keywords

• Distinguished private and public extension values in type and method fields

• Added a "Creation Time" tEXt keyword

• Macintosh representation of PNG specified

• Added discussion of security issues

• Added more extensive discussion of gamma and chromaticity handling, including tutorial appendixes

• Clarified terminology, notably sample depth vs. bit depth

• Added a glossary

• Editing and reformatting