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

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.


>
> 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
>
>