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

From: Dirk Schulze <dschulze@adobe.com>
Date: Tue, 24 Dec 2013 07:57:40 +0000
To: Simon Fraser <smfr@me.com>
CC: Rik Cabanier <cabanier@gmail.com>, David <david.email@ymail.com>, www-style list <www-style@w3.org>
Message-ID: <36A0BAA5-1454-42A3-9398-D486FE5B557F@adobe.com>

On Dec 24, 2013, at 8:47 AM, Dirk Schulze <dschulze@adobe.com> 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));

Just to give a bit more background: The filter() image function is specified in Filter Effects[1] and allows filtering other CSS Images:

	filter( [ <image> | <string> ], <filter-function-list> )

opacity() is one of the filter functions beside others [2].

Greetings,
Dirk

[1] http://dev.w3.org/fxtf/filters/#FilterCSSImageValue
[2] http://dev.w3.org/fxtf/filters/#FilterProperty

> 
> Greetings,
> Dirk
> 
>> 
>> Simon
>> 
> 
> 
Received on Tuesday, 24 December 2013 07:58:12 UTC

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