PNG (Portable Network Graphics) Specification, Version 0.90
Revision date: 3 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 status of spaces in tEXt chunk keywords
- Macintosh representation of PNG specified
- Added discussion of security issues
- Added a glossary
Issues not yet clarified in this working draft include:
- Interpretation of a suggested-palette PLTE chunk in an
RGB image that includes alpha channel or tRNS chunk.
- Exact semantics of sBIT: is encoder required to use only
as many distinct sample values as are implied by sBIT?
- Additional standard tEXt keywords are under consideration.
- Additional explanatory material for gamma and cHRM
processing is planned.
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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