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Re: Errata for PNG spec (tRNS chunk)

From: David Duce <daduce@brookes.ac.uk>
Date: Fri, 26 Jun 2009 12:20:31 +0100
Message-ID: <4A44AEFF.8030203@brookes.ac.uk>
To: Chris Lilley <chris@w3.org>, Glenn Randers-Pehrson <glennrp@gmail.com>
CC: PNG/MNG discussion list <png-mng-misc@lists.sourceforge.net>, www-archive@w3.org, david Duce <daduce@brookes.ac.uk>
Chris, Glenn,

I've had an email exchange with Jean Stride at BSI. Jean also runs some 
of the key ISO Committees.

It turns out that the ISO Committees are meeting in London in 10 days 
time. ISO has a process for Technical Corrigenda, which involve ballots. 
Jean is looking into whether this item could be considered at the London 
meetings. If it could it is likely to save considerable effort. But we 
will have to move very quickly if they agree to consider it.

Jean has contacted the chair of the meeting, Dick Puk, to see if he can 
help. You may recall that Dick participated in some of our meetings.

If I get a positive response, has enough process been completed on the 
W3C side for me to effectively say to Dick that W3C has approved this 
erratum through its processes and hence we now invite ISO/IEC to do 

I've looked back through some old files. This error must have creapt in 
very early on. Certainly the PNG 1.1 and 1.2 drafts I have use the RGB 
order. The error is in the first Committee Draft sent to ISO/IEC and the 
corresponding BSI Draft for Public Comment dated 98-12-01. But I have at 
least one document which doesn't contain the error - that's an internal 
document where we'd started the conversion to ISO/IEC format.

Best regards


Chris Lilley wrote:
> On Thursday, June 25, 2009, 1:20:51 AM, Glenn wrote:
> GRP> Chris,
> GRP> In clause (tRNS chunk), the table entry for colour type 2 has
> GRP> the green and blue samples in the wrong order.
> GRP> It should read:
> GRP>      Colour type 2
> GRP>      Red sample value      2 bytes
> GRP>      Green sample value  2 bytes
> GRP>      Blue sample value     2 bytes
> Glenn,
> Thanks for the report.
> The W3C process for errata management is described at
> http://www.w3.org/2005/10/Process-20051014/tr.html#rec-modify
> In accordance with that document I have updated the errata document
> (this is the first reported erratum).
> http://www.w3.org/2003/11/REC-PNG-20031110-errata.html
> Since the original PNG specification had the correct order, and since
> the order Red, Blue, Green is used nowhere else in the specification,
> it looks as if implementations have silently corrected for the obvious
> typo. Thus, this erratum does not alter conformance and I have
> classified it accordingly.
> Is anyone aware of any implementation which followed the letter of PNG
> second edition here (and would thus become nonconformant)?
> Please review the proposed erratum, even though the error is simple
> and obvious.
> I wonder if a simple test case, say a PNG image with two colors, one
> of which is transparent if the erratum (or PNG first edition) is
> followed and the other of which is transparent if PNG second edition
> had been followed, would be a useful addition?
> Since this specification was published as both a W3C Recommendation
> and as an ISO Standard, I have copied David Duce since the proposed
> correction (despite being trivial) needs to be reported to ISO. I
> assume that they will issue a Technical Corrigendum, but welcome
> guidance from David here.

Professor David Duce

School of Technology
Oxford Brookes University
Wheatley Campus
OX33 1HX

email: daduce@brookes.ac.uk
tel: +44 (0) 1865 484528
fax: +44 (0) 1865 484545
Received on Friday, 26 June 2009 11:19:24 UTC

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