Re: Meeting minutes - Aug 8th, 2022

I have to agree on the error handling text vs. sample files.

One thing that I am pushing in the JPEG committees is that any “reference software” *MUST* include a test suite containing both valid and invalid files.  I think we should consider the same here – and it fits nicely into the “testability” requirements of W3C.

Leonard

From: Chris Blume (ProgramMax) <programmax@gmail.com>
Date: Monday, August 8, 2022 at 11:56 AM
To: public-png@w3.org <public-png@w3.org>
Subject: Meeting minutes - Aug 8th, 2022

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Attached is a PDF of the meeting minutes from Aug 8th, 2022.

Executive summary:

  *   PNG encoders and decoders are already strongly motivated to behave well (displaying what they can, for example). Any error handling wording we add to the spec to encourage this would not provide additional motivation. Instead, if we want to encourage good error handling behavior we should provide sample images to validate error cases.
  *   We should be firm on PNG encoders to not write out-of-bounds palette indices. For decoders, we can provide a note which mentions that different decoders behave differently and there are images in the wild which abuse this.
  *   Further research is needed to make a decision about the unused trailing bytes in a compression stream.
  *   The PNG spec wording should change away from claiming unused high bits of bKGD and tRNS values "are zero". The wording should instead be along the lines of "should be zero". Additionally, the spec should mention that these bits are ignored. This change clarifies that this is not an error condition.
  *   There are several issues with the definitions section. At the moment, it seems like trimming the definition section will act as a common solution to these issues.
The next meeting will be Aug 22nd, 2022 from 11am-noon Eastern US time.

A future email will list topics for that meeting.