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[WebVTT] It's not easy being green

From: Michael Dolan <mdolan@newtbt.com>
Date: Mon, 16 Mar 2015 17:03:01 -0700
To: <public-tt@w3.org>
Message-ID: <025a01d06045$bc7e0610$357a1230$@newtbt.com>
I received an email from someone studying SMPTE-TT and WebVTT who wrote and
presented a paper about 18 months ago titled, "'It's not easy being green -
a closed captioning for web case study'".  Among other things, he observed
that we map CEA 608 "green" to SVG/CSS3 "green".


FYI, the SVG/CSS3 RGB value of "green" is 008000, not 00FF00 you might
expect (which is the color "lime"):


Note in contrast that "red" and "blue" are both full brightness.


Of the various 608 mapping documents..SDP-US uses only RGB values (no color
names) and explicitly defines "green" to be 00FF00.  However both SMPTE-TT
(RP2052-10) and WebVTT say to map 608 "green" to TTML "green" which is
minimally inconsistent with SDP-US. The same would be true for 708 mappings,
of course.


Of historical note, CSS1 says the color palette came from the "Windows VGA
palette", which seems to have come from the CGA text color palette:


(although the above  defines the brighter green as "light green").


We could assume it is supposed to be maximum brightness like "red" and
"blue" (i.e. 00FF00), but on the off chance that "green" text overlay is
actually handled differently in the billion TV's out there I'll ask a couple
of set manufacturers..







Michael A DOLAN

TBT, Inc. PO Box 190

Del Mar, CA 92014

(m) +1-858-882-7497

Received on Tuesday, 17 March 2015 00:03:31 UTC

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