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Re: Issue-224 3D approach - disparity rather than (translation and condition)

From: Glenn Adams <glenn@skynav.com>
Date: Tue, 20 Jan 2015 14:47:43 -0700
Message-ID: <CACQ=j+d2afnS3ram6CUJkngJ0V+z=2FmSuaPBWx6coM3oJdwgQ@mail.gmail.com>
To: Nigel Megitt <nigel.megitt@bbc.co.uk>
Cc: Pierre-Anthony Lemieux <pal@sandflow.com>, TTWG <public-tt@w3.org>
my position is that a translate property is more generally applicable than
a diversity property, and the latter can be expressed using the former.
pierre agrees with the latter, so i comsider this issue closed

On Tuesday, January 20, 2015, Nigel Megitt <nigel.megitt@bbc.co.uk> wrote:

>
>
>
> > On 20 Jan 2015, at 18:15, Pierre-Anthony Lemieux <pal@sandflow.com
> <javascript:;>> wrote:
> >
> > Hi Nigel et al.,
> >
> >> are there pre-existing implementations that take
> >> this approach of direct translation with conditional offset values?
> >
> > Issue-224 was motivated by a SMPTE liaison (SEPT 2012) and references
> > D-Cinema subtitles (SMTPE ST 428-7). In the latter, rendering of
> > subtitles to left- and right-eye stereoscopic images is controlled
> > using an attribute ("ZPosition") that specifies the disparity (as a
> > percentage of the root container) between left- and right-eye images.
> >
> > """When present, the Zposition attribute shall provide a value that
> > specifies the horizontal distance between the “left eye” image center
> > and the “right eye” image center - in order to generate a stereoscopic
> > effect."""
> >
> > Minimally, I would think that the approach selected by TTWG should
> > support the D-Cinema approach, which is implemented.
>
> Thanks Pierre,
>
> That sounds exactly coincident with my proposal for disparity.
>
> Nigel
>
> >
> > Best,
> >
> > -- Pierre
> >
> >> On Tue, Jan 20, 2015 at 8:43 AM, Nigel Megitt <nigel.megitt@bbc.co.uk
> <javascript:;>> wrote:
> >> From: Glenn Adams <glenn@skynav.com <javascript:;>> Date: Tuesday, 20
> January 2015 14:37
> >>
> >>
> >>
> >> On Tue, Jan 20, 2015 at 3:22 AM, Nigel Megitt <nigel.megitt@bbc.co.uk
> <javascript:;>>
> >> wrote:
> >>>
> >>> Glenn,
> >>>
> >>> I see you have created update
> https://dvcs.w3.org/hg/ttml/rev/abebbd0a303b
> >>> to address issue-224, for 3D disparity. It looks as though the approach
> >>> you've taken is to allow the same document to be processed twice, once
> for
> >>> the left image and once for the right image for a stereoscopic display,
> >>> and to allow translation to be specified, being dependent on a
> parameter
> >>> and using the condition attribute.
> >>
> >>
> >> I discussed this thoroughly with Pierre before publishing this
> approach, and
> >> we are both in agreement that it can handle the requirements. So that's
> what
> >> I'm going with.
> >>
> >>
> >> I don't disagree that an author can, with care, craft a document that
> will
> >> display stereoscopically with the correct characteristics using this
> >> technique, however "can handle" is not equal to "best way to express
> this
> >> information".
> >>
> >> Pierre,  are there pre-existing implementations that take this approach
> of
> >> direct translation with conditional offset values? 3D subtitles using a
> >> single disparity value are in common usage as per the links I sent (now
> >> below).
> >>
> >>
> >>>
> >>>
> >>> Can I propose an alternate way to achieve stereoscopic object placement
> >>> that may be more amenable to simple, i.e. single pass, processing? This
> >>> would be to add a tts:disparity style attribute, whose value would be a
> >>> <length>, positive or negative. This would be inherited and animatable,
> >>> and apply to region, div or p (possibly a span too). Positive values
> imply
> >>> that the image is behind the plane of display and negative values imply
> >>> that the image is in front of the plane of display.
> >>>
> >>> For example see [1] §4.2.1. Following the references, this seems to be
> how
> >>> it's done in DVB [2].
> >>>
> >>> [1] ETSI TS 101 600 C1.1.1 (2012-05)
> >>>
> >>>
> http://www.etsi.org/deliver/etsi_ts/101600_101699/101600/01.01.01_60/ts_101
> >>> 600v010101p.pdf
> >>> [2] ETSI EN 300 743 V1.4.1 (2011-10)
> >>>
> >>>
> http://www.etsi.org/deliver/etsi_en/300700_300799/300743/01.04.01_60/en_300
> >>> 743v010401p.pdf
> >>>
> >>> A good description from [2] (p. 34) is:
> >>>
> >>>> Disparity is the difference between the horizontal positions of a
> pixel
> >>>> representing the same point in space in the right and left views of a
> >>>> plano-stereoscopic image. Positive disparity values move the subtitle
> >>>> objects enclosed by a subregion away from the viewer whilst negative
> >>>> values move them towards the viewer. A value of zero places the
> objects
> >>>> enclosed by that subregion in the plane of the display screen.
> >>>
> >>>
> >>> And from a little further down:
> >>>
> >>>> A positive disparity shift value for example of +7 will result in a
> >>>> shift of 7 pixels to the left in the left subtitle subregion image
> and a
> >>>> shift of 7 pixels to the right in the right subtitle subregion image.
> A
> >>>> negative disparity shift value of -7 will result in a shift of 7
> pixels
> >>>> to the right in the left subtitle subregion image and a shift of 7
> pixels
> >>>> to the left in the right subtitle subregion image. Note that the
> actual
> >>>> disparity of the displayed subtitle is therefore double the value of
> the
> >>>> disparity shift values signalled in the disparity integer and/or
> >>>> fractional fields […]
> >>>
> >>> Kind regards,
> >>>
> >>> Nigel
> >>
>
Received on Tuesday, 20 January 2015 21:48:11 UTC

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