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Re: [css3-background] A property to control background opacity

From: Alan Gresley <alan@css-class.com>
Date: Wed, 25 Dec 2013 02:22:40 +1100
Message-ID: <52B9A6C0.9040406@css-class.com>
To: Dirk Schulze <dschulze@adobe.com>, Simon Fraser <smfr@me.com>
CC: Rik Cabanier <cabanier@gmail.com>, David <david.email@ymail.com>, www-style list <www-style@w3.org>
On 24/12/2013 6:47 PM, Dirk Schulze wrote:
> On Dec 24, 2013, at 8:34 AM, Simon Fraser <smfr@me.com> wrote:
>> On Dec 23, 2013, at 7:06 PM, Rik Cabanier <cabanier@gmail.com> wrote:
>>> On Mon, Dec 23, 2013 at 4:33 PM, David <david.email@ymail.com> wrote:
>>> Hello,
>>> it would be great if a CSS property would be added to control the opacity of the background-image.
>>> The background-color and its opacity is already controlable via rgba() or hsla().
>>> The opacity property itself allows just to control the opacity of the whole element.
>>> We had a short discussion on this at the last F2F during TPAC [1].
>>> It was unfortunately not minuted. :-(
>>> During the meeting, people said that this feature has been requested for a long time but for some reason, it never was spec'ed out or implemented.
>>> Normative text could look as follows:
>>> The ‘background-opacity’ property
>> An alternative to this would be to have an image function that gives an image alpha, e.g.:
>> background-image: alpha-image(foo.png, 50%);
>> This would seem preferable to a property that can only apply alpha to background images.
> Just to give more alternatives: In WebKit the CSS Image function -webkit-filter() is implemented with the opacity filter function:
> background-image: -webkit-filter(foo.png, opacity(0.5));
> Greetings,
> Dirk

You would want to apply it to different background layers. It can be 
done already by applying opacity to a referenced element via 'element()' 
in background-image but that is a hack.

I support 'background-opacity' or something like 'background-filter' 
since you can animate a numerical value. I believe it's not future proof 
to use opacity buried in a value within parenthesis that is already 
nested in a value within parenthesis like 'filter(foo.png, 
opacity(0.5))'. Something like the below is also simpler for an author 
to follow.

   background-image: url(), linear-gradient();
   background-filter: blur(20px), opacity(0.5);


Alan Gresley
Received on Tuesday, 24 December 2013 15:23:13 UTC

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