PNG (Portable Network Graphics) Specification, Version 0.91
Revision date: 8 November, 1995
This is a working draft of the PNG specification. It is not intended
for public distribution. A public release of version 1.0 is planned
shortly.
The PNG format has been frozen since the Ninth Draft, and all future
changes are intended to be backwards compatible. The revisions
planned for version 1.0 are simply clarifications, improvements in
presentation, and additions of supporting material. Several
implementations already exist, and more are in progress.
Changes since the Tenth Draft of 5 May, 1995
- Extensive editing
- Clarified meaning of a suggested-palette PLTE chunk in a
truecolor image that uses transparency
- Clarified exact semantics of sBIT and allowed bit depth
scaling procedures
- Clarified status of spaces in tEXt chunk keywords
- Added a "Creation Time" tEXt keyword
- Macintosh representation of PNG specified
- Added discussion of security issues
- Added a glossary
- Added more extensive discussion of gamma handling
Items not yet completed in this working draft include:
- Additional standard tEXt keywords are under consideration.
- Additional explanatory material for cHRM processing is planned.
- Non-draft versions of the deflate and zlib specifications need to
be generated. No technical changes are believed needed in those documents.
All these items will be completed before version 1.0 is issued.
Standardization plans
The PNG development group intends to submit the PNG format to the
World Wide Web Consortium for adoption as a W3C standard. If adopted,
the copyright on the PNG spec will be assigned to W3C.
An Internet RFC for PNG is also planned.
Archive sites
The latest versions of this document and related information can
always be found at the PNG FTP archive site,
ftp.uu.net:/graphics/png/.
The maintainers of the PNG specification can be contacted by e-mail at
png-info@uunet.uu.net.
At present, this document is available on the World Wide Web from
http://sunsite.unc.edu/boutell/png.html
,
but this location may not be as permanent as the ones above.
Reference implementation and test images
A reference implementation in portable C is available from the PNG FTP
archive site,
ftp.uu.net:/graphics/png/src/.
The reference implementation is freely usable in all
applications, including commercial applications.
Test images are available from the same archive in
ftp.uu.net:/graphics/png/images/.
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