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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
transparent.

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

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