[ttml2] disparity "closest supported value" language misleading

nigelmegitt has just created a new issue for 
https://github.com/w3c/ttml2:

== disparity "closest supported value" language misleading ==
There's a note on `tts:disparity` that says:

> In this context, the phrase closest supported value means the value 
for which the Euclidean distance between the computed disparity and 
the supported disparity is minimized. If there are multiple closest 
supported values equally distant from the computed value, then the 
value least distant from 0 is used.

This is slightly misleading since it does not point out that for 
correct display of stereoscopic content sub-pixel rendering is 
important. See [this 
thread](https://lists.w3.org/Archives/Public/public-tt/2015Jan/0041.html)
 where we discussed this previously.

I suggest we either keep this (because it is formally correct) and add
 a note along the lines of:

> The presentation of stereoscopic content depends in general on the 
use of sub-pixel (anti-aliasing) rendering techniques; implementations
 that quantise region position as adjusted by disparity to an integer 
pixel value may create undesirable visual effects. This is 
particularly important when there is a smooth animation of disparity, 
for example to maintain a constant distance between the subject and 
the text in front of it.

Please view or discuss this issue at 
https://github.com/w3c/ttml2/issues/153 using your GitHub account

Received on Friday, 4 March 2016 13:51:39 UTC