Re: Meeting minutes - Aug 8th, 2022

Agreed – it is not part of the standard.  But in the same way that we (at least unofficially) reference libpng – we should reference a test suite.   I wasn’t familiar with PngSuite – and it seems like a great start.  It appears to not have been updated since 2011 – perhaps we can reach out to Willem and see what plans he may have, if we could take it over, etc?

Leonard

From: Chris Blume (ProgramMax) <programmax@gmail.com>
Date: Monday, August 8, 2022 at 12:23 PM
To: Leonard Rosenthol <lrosenth@adobe.com>
Cc: public-png@w3.org <public-png@w3.org>
Subject: Re: Meeting minutes - Aug 8th, 2022

EXTERNAL: Use caution when clicking on links or opening attachments.


I agree.
Although, I don't know how to make them part of the standard, per se. I think the sample images could be provided alongside the standard as a helpful tool but not part of the standard itself.

In that regard, PngSuite<https://nam04.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.schaik.com%2Fpngsuite%2F&data=05%7C01%7Clrosenth%40adobe.com%7C8bdb0e17cb29442a5e5908da795a43e2%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C0%7C637955725843926257%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=XA1vDRM%2B6AD6IP3ITuk5MqcG9ugL3pu2uGWEsUNUL7I%3D&reserved=0> [1] already does a great job while not being part of the standard. Maybe we can add a mention to it somewhere if we aren't already.

[1] http://www.schaik.com/pngsuite/<https://nam04.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.schaik.com%2Fpngsuite%2F&data=05%7C01%7Clrosenth%40adobe.com%7C8bdb0e17cb29442a5e5908da795a43e2%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C0%7C637955725843926257%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=XA1vDRM%2B6AD6IP3ITuk5MqcG9ugL3pu2uGWEsUNUL7I%3D&reserved=0>

On Mon, Aug 8, 2022 at 12:00 PM Leonard Rosenthol <lrosenth@adobe.com<mailto:lrosenth@adobe.com>> wrote:
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<mailto:programmax@gmail.com>>
Date: Monday, August 8, 2022 at 11:56 AM
To: public-png@w3.org<mailto:public-png@w3.org> <public-png@w3.org<mailto:public-png@w3.org>>
Subject: Meeting minutes - Aug 8th, 2022

EXTERNAL: Use caution when clicking on links or opening attachments.


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.