W3C home > Mailing lists > Public > public-tt@w3.org > August 2006

Re: Color fidelity during transcoding

From: Chris Lilley <chris@w3.org>
Date: Tue, 29 Aug 2006 23:10:48 +0200
Message-ID: <796059158.20060829231048@w3.org>
To: Dave Singer <singer@apple.com>
Cc: "Glenn A. Adams" <gadams@xfsi.com>, public-tt@w3.org

On Friday, August 25, 2006, 6:49:27 PM, Dave wrote:

DS> I'm not sure I understand what's going on here.  We needed to define 
DS> what the numeric R G and B values in our colours meant.  We say that 
DS> they are as defined in the sRGB specification.

Yes, I'm very clear on that point.

DS> If you then take our content and render it on a system with different 
DS> colour characteristics, it's your job to work out the colour 
DS> transforms and corrections that need to be applied.  This is strictly 
DS> out of scope for a timed text specification.  It's in scope for the 
DS> sRGB specification, and I believe it's covered there.

Since timed text is aimed at both broadcast systems and web-based systems, it seemed that a small amount of guidance was merited when moving between one and the other. 

DS> We could insert an informative note that if timed text is composed 
DS> with content, or rendered onto drawing surfaces, that have other 
DS> colour spaces or formats, then the colours may need conversion to 
DS> preserve visual fidelity, but more than that is surely not our job.

That was the area where I suspected some advice and guidance would help.

DS> Unless you feel that sRGB is under-specified, whereupon we should 
DS> choose a colour space that is fully specified instead, of course.

I consider it to be well specified, and indeed I contributed to the specification. I am also aware that it uses very different viewing conditions to broadcast color spaces. Some guidance to implementors therefore seemed in order.

DS> So sure, I agree, you can't take sRGB values and blast them onto a 
DS> 709 display without doing colour space conversion,


DS>  but do we suggest 
DS> you can?  Why would you think you could?

I don't think you can, but then I have some grasp of color theory. I suspect that people who do not, will do exactly that.

 Chris Lilley                    mailto:chris@w3.org
 Interaction Domain Leader
 Co-Chair, W3C SVG Working Group
 W3C Graphics Activity Lead
 Co-Chair, W3C Hypertext CG
Received on Tuesday, 29 August 2006 21:11:12 UTC

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