RE: opacity & alpha

There are 4 responses that seem to be a little different. I like this one J

 

From: Glenn Adams [mailto:glenn@skynav.com] 
Sent: Sunday, May 12, 2013 5:52 PM
To: Michael A Dolan
Cc: public-tt
Subject: 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.

 

The schema datatypes module defines:

 

1.       “alpha” but constrains it to 0-1.  A good idea, but wrong.

 

Not sure how 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.

The prose was based on the definition of <alphavalue> in CSS3 Color Module which uses the same formalism. 

2.       Either way, the schema be changed to use the “alpha” datatype (however we define it).

I've updated the XSD definition of opacity to use ttd:alpha instead of xs:string.

 

 

Regards,

 

                Mike

 

 

Michael A DOLAN

Television Broadcast Technology, Inc

PO Box 190, Del Mar, CA 92014 USA

+1-858-882-7497 <tel:%2B1-858-882-7497>  (m)