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Re: Opacity 0-1: Bad Idea?

From: J. David Eisenberg <catcode@catcode.com>
Date: Sun, 11 Nov 2001 15:53:42 -0600 (CST)
To: Andy <lordpixel@mac.com>
cc: www-style@w3.org
Message-ID: <Pine.LNX.3.96.1011111153859.18214A-100000@tengu.host4u.net>
On Sun, 11 Nov 2001, Andy wrote:

> Dmitry Beransky wrote:
> > 
> > Actually, I can see why Kevin might have thought so.  The spec says:
> > 
> >    Any values outside the range 0.0 (fully transparent) to 1.0
> >    (fully opaque) will be clipped to this range.
> > 
> > using '0.0' and '1.0' instead of '0' and '1'. Strictly speaking, this
> > implies that the precision is only to the first decimal position.
> This is all very nice, but ultimately, it would be *much* clearer as a
> percentage: 
> opacity:100%; //yup. looks like fully opaque to me
> opacity:10%; // that reads as pretty transparent to me
> opacity:1; // well, might be 100% opaque I suppose
> opacity:0.6; // is that just more than halfway transparent? or just less?

It would be clearer as a percentage, and probably not too much trouble
to parse.  However, I'd leave the decimal notation; style sheets or
inline styles can be generated programmatically, and it's easier not to
have to convert to a percent.

> Of course, since everyone I've ever spoken to refers to the effect as
> "transparency" and pretty much everything is 100% opaque by default and
> one only needs to trot out the opacity attribute if one wants to make
> something "somewhat transparent", I've never understood why its not 
> transparency:75%; //three quarters see through - now that makes sense...
> No one says "that pane of glass in that window is semi-opaque". It would
> always be "transparent" (or translucent!). Its just not English!
> Since CSS3 is not final, now's the ideal time to change!

Transparency is much more natural in spoken language among humans.  I've
been doing some writing about SVG, and it's been a pain to have to refer
to "opacity" instead. However, transparency should be an _additional_
property, not a replacement. You really want "backward compatibility," so
to speak, with things like SVG that have established the convention. 

From my reading of the CSS3 documents, opacity represents an image's 
alpha channel.  A lot of graphic folks are already familiar with
this concept, and in an alpha channel, 100% is opaque and 0% is

J. David Eisenberg  http://catcode.com/
Received on Sunday, 11 November 2001 17:07:45 UTC

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