Re: opacity & alpha

On Fri, Jun 22, 2012 at 5:13 PM, Michael A Dolan <mdolan@newtbt.com> wrote:

> Alpha, used for opacity, is defined to be any real number.  The prose goes
> on to say: If the value represented is less than 0.0, then it must be
> interpreted as equal to 0.0; similarly, if the value represented is greater
> than 1.0, then it must be interpreted as 1.0.
>

I did it this way because that's how CSS3 Color defined <alphavalue> [1].

[1] http://www.w3.org/TR/css3-color/#transparency


> ****
>
> ** **
>
> The schema datatypes module defines:****
>
> ** **
>
> **1.       **“alpha” but constrains it to 0-1.  A good idea, but wrong.
>
Why this is "wrong"?


>  ****
>
> **2.       **“opacity” as xs:string (doesn’t use “alpha”)****
>
> ** **
>
> I can’t think of why a dataype, “alpha”, should be other than 0-1, and it
> is not used for anything else in TTML.  So I propose:
>
> ****
>
> **1.       **The prose be changed to constrain it to 0-1 and remove the
> text quoted above about what to do if it isn’t.
>
I guess I'd prefer to keep it defined as CSS3 defines alphavalue, unless
there is a substantive difference between the two.

> ****
>
> **2.       **Either way, the schema be changed to use the “alpha”
> datatype (however we define it).
>
I've changed the XSD to define opacity by using the ttd:alpha data type.


> ****
>
> ** **
>
> Regards,****
>
> ** **
>
>                 Mike****
>
> ** **
>
> ** **
>
> Michael A DOLAN****
>
> Television Broadcast Technology, Inc****
>
> PO Box 190, Del Mar, CA 92014 USA****
>
> +1-858-882-7497 (m)****
>
> ** **
>