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Conversion of 608/708 captions to WebVTT - how to map the colour green

From: Michael Borthwick <mb@michaelborthwick.com.au>
Date: Tue, 25 Mar 2014 12:16:51 +1100
Message-Id: <598BD46D-2F46-43EF-88BB-E593AEBAF404@michaelborthwick.com.au>
To: public-texttracks@w3.org
Dear List Members,

I am Australian media engineer who wrote a technical paper, presented  
last year at the SMPTE 2013 Conference in Sydney, entitled "It's not  
easy being green - a closed captioning for web case study'.
This dealt with the making some hundreds of closed captioned video  
clips available on a client web site in 2011 using DFXP format and JW  
One of a number of hurdles that were overcome in that project was  
gaining an understanding of, and overcoming, an apparent semantic  
difference between the colour green when used for closed captions and  
subtitles in the broadcast industry and that on the web.

To speak to the essence of a 5 page technical paper I formed the  
opinion that it is the intention in the broadcast world, in standards  
such as CEA608/708 and the European DVB standard (used in Australia)  
that the colour green means that the green value be at its maximum ie  
in 8 bit RGB (decimal) 0 255 0.

Colour captions are commonly used in Australia to distinguish between  
speakers and are particularly relevant to clarify meaning for the Deaf  
or hearing impaired viewer when the speaker is off screen - although  
green is arguably the least common of the four colours used.

Literally translating the occurrence of 'green' from a broadcast  
standard into a web caption standard that leverages CSS specifications  
for green of RGB  (hexadecimal) 008000 yields a darker green with  
inadequate contrast as the green channel is not at its maximum.

I would therefore respectfully suggest that the WebVTT Community  
Group, in common with others developing cross-domain conversion  
standards, revisit the assumption that CEA608 and 708 colours 'map to  
CSS colors of the same name' as suggested in Clause 1.6 of the Draft  
of the conversion document at https://dvcs.w3.org/hg/text-tracks/raw-file/default/608toVTT/608toVTT.html

If the desire is to map to a named colour then a more appropriate  
named colour might be 'lime' in order to more accurately capture what  
I believe to be the broadcast intent.

it is my understanding, based on personal communication with engineers  
from the BBC undertaken after the conclusion of my project, that this  
is the parsing used when caption files in broadcast formats are mapped  
for web display on the BBC's many public-facing platforms.

While the slides from my presentation are available from my LinkedIn  
profile, and the paper was made available to conference to attendees,  
is not publicly available on the web.
However I am happy to respond to requests off-list should it be of  
interest to individual members of the Community Group.

Thankyou for your interest in this important area of web accessibility.



Michael Borthwick Consulting Pty. Ltd.
GPO Box 1950, 380 Bourke Street, Melbourne Australia 3001
Level 1, 384 Bridge Road, Richmond
Mobile Ph: + 61 418 345 800
Received on Tuesday, 25 March 2014 10:34:05 UTC

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