Re: ISSUE-318 (HRM glyph copy assumes no sub-pixel positioning): Hypothetical Render Model glyph copy assumes no sub-pixel positioning [TTML IMSC 1.0]

On 22/05/2014 15:44, "Michael Dolan" <mdolan@newtbt.com> wrote:

>This and issue 317 call to light the difference between alignment with
>the related media (video) object versus display rendering.

Yes - I've been thinking the same thing.

> All that can really be contemplated by an author is alignment with the
>related coded video, not how the resulting  decoded video+text is mapped
>to an (entirely unknown to the author) display resolution, framerate, etc.

I disagree here - all that can be contemplated by an author is alignment
with the video available at the time of authoring. Intervening workflows
need to be taken into account. The related encoded video that is made
available may have a different display resolution, framerate etc, and the
decoded video and text will have yet another display resolution and
framerate.

>
>The HRD is ONLY about document conformance.

This brings to mind issue 315 too, which defines a maximal content
constraint that I suggest should be changed to a minimal processor
constraint. I'd do consider doing the same for the HRM, i.e. it can be
used to define test content that a minimally compliant processor must be
able to process successfully, or conversely, can be used to check content
that a processor under test fails to process correctly to see if the cause
is a fault in the processor fault or over-complex content.

In both cases by specifying minimal processor compliance it is then
possible to create a processor sub-profile with a higher minimal
compliance level that is also able to process documents conforming to the
base-level profile. This opens up the path to future enhancements, rather
than blocking it at source, or requiring a whole new, almost identical
content profile that differs only in maximum compliance thresholds.

Kind regards,

Nigel


>
> Mike
>
>-----Original Message-----
>From: Timed Text Working Group Issue Tracker
>[mailto:sysbot+tracker@w3.org]
>Sent: Thursday, May 22, 2014 4:13 AM
>To: public-tt@w3.org
>Subject: ISSUE-318 (HRM glyph copy assumes no sub-pixel positioning):
>Hypothetical Render Model glyph copy assumes no sub-pixel positioning
>[TTML IMSC 1.0]
>
>ISSUE-318 (HRM glyph copy assumes no sub-pixel positioning): Hypothetical
>Render Model glyph copy assumes no sub-pixel positioning [TTML IMSC 1.0]
>
>http://www.w3.org/AudioVideo/TT/tracker/issues/318
>
>Raised by: Nigel Megitt
>On product: TTML IMSC 1.0
>
>IMSC 1 FPWD includes in the Hypothetical Render Model a test for how two
>glyphs can be considered identical for buffer copying purposes. This does
>not take into account sub-pixel positioning of anti-aliased text, which
>would result in different per-pixel buffer values for a glyph that would
>otherwise be considered identical using the current criteria.
>
>For presentation devices that layout text using sub-pixel accuracy and
>render glyphs with anti-aliasing this test of identity will fail
>resulting in wrongly painted glyphs.
>
>I propose that an extra criterion is added to the glyph identity test
>that the post-layout sub-pixel offset relative to the pixel grid,
>horizontally and vertically, is identical.
>
>[1] 
>https://dvcs.w3.org/hg/ttml/raw-file/ea1a92310a27/ttml-ww-profiles/ttml-ww
>-profiles.html#paint-text
>
>
>
>



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Received on Thursday, 22 May 2014 16:00:38 UTC