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

---------- Forwarded message ----------
From: *Glenn Adams* <glenn@skynav.com>
Date: Wednesday, January 21, 2015
Subject: Issue-224 3D approach - disparity rather than (translation and
condition)
To: Nigel Megitt <nigel.megitt@bbc.co.uk>




On Wed, Jan 21, 2015 at 2:26 AM, Nigel Megitt <nigel.megitt@bbc.co.uk
<javascript:_e(%7B%7D,'cvml','nigel.megitt@bbc.co.uk');>> wrote:

>  I don't believe we have achieved consensus on this issue yet, so we can
> not consider it to be closed.
>
>  What other applications for the translate property do you have in mind?
>

I'm considering allowing it to be applied to span, to effect local position
adjustments. Also animation effects. It may eventually be joined by rotate
and scale, effectively mapping to a full transform property.


>
>
>
>   From: Glenn Adams <glenn@skynav.com
> <javascript:_e(%7B%7D,'cvml','glenn@skynav.com');>>
> Date: Tuesday, 20 January 2015 21:47
> To: Nigel Megitt <nigel.megitt@bbc.co.uk
> <javascript:_e(%7B%7D,'cvml','nigel.megitt@bbc.co.uk');>>
> Cc: Pierre-Anthony Lemieux <pal@sandflow.com
> <javascript:_e(%7B%7D,'cvml','pal@sandflow.com');>>, TTWG <
> public-tt@w3.org <javascript:_e(%7B%7D,'cvml','public-tt@w3.org');>>
> Subject: Re: Issue-224 3D approach - disparity rather than (translation
> and condition)
>
>   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
> <javascript:_e(%7B%7D,'cvml','nigel.megitt@bbc.co.uk');>> wrote:
>
>>
>>
>>
>> > On 20 Jan 2015, at 18:15, Pierre-Anthony Lemieux <pal@sandflow.com>
>> 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>
>> wrote:
>> >> From: Glenn Adams <glenn@skynav.com> Date: Tuesday, 20 January 2015
>> 14:37
>> >>
>> >>
>> >>
>> >> On Tue, Jan 20, 2015 at 3:22 AM, Nigel Megitt <nigel.megitt@bbc.co.uk>
>> >> 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
>> >>
>>
>