CSS 背景-图像-不透明度? ？

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You can't edit the image via CSS. The only solution I can think of is to edit the image and change its opacity, or make different images with all the opacities needed.

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最佳答案

If the background doesn't have to repeat, you can use the sprite technique (sliding-doors) where you put all the images with differing opacity into one (next to each other) and then just shift them around with background-position.

Or you could declare the same partially transparent background image more than once, if your target browser supports multiple backgrounds (Firefox 3.6+, Safari 1.0+, Chrome 1.3+, Opera 10.5+, Internet Explorer 9+). The opacity of those multiple images should add up, the more backgrounds you define.

This process of combining transparencies is called Alpha Blending and calculated as (thanks @IainFraser):

αᵣ = α₁ + α₂(1-α₁) where α ranges between 0 and 1.

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You can do the faded background with CSS Generated Content

Demo at http://jsfiddle.net/gaby/WktFm/508/

Html

<div class="container">
contents
</div>

Css

.container{
position: relative;
z-index:1;
overflow:hidden; /*if you want to crop the image*/
}
.container:before{
z-index:-1;
position:absolute;
left:0;
top:0;
content: url('path/to/image.ext');
opacity:0.4;
}

But you cannot modify the opacity as we are not allowed to modify generated content..

You could manipulate it with classes and css events though (but not sure if it fits your needs)

for example

.container:hover:before{
opacity:1;
}

UPDATE

You can use css transitions to animate the opacity (again through classes)

demo at http://jsfiddle.net/gaby/WktFm/507/

Adding

-webkit-transition: opacity 1s linear;
-o-transition: opacity 1s linear;
-moz-transition: opacity 1s linear;
transition: opacity 1s linear;

to the .container:before rule will make the opacity animate to 1 in one second.

Compatibility

FF 5 (maybe 4 also, but do not have it installed.)
IE 9 Fails..
Webkit based browsers fail (Chrome supports it now v26 - maybe earlier versions too, but just checked with my current build), but they are aware and working on it ( https://bugs.webkit.org/show_bug.cgi?id=23209 )

.. so only the latest FF supports it for the moment.. but a nice idea, no ? :)

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You can put a second element inside the element you wish to have a transparent background on.

<div class="container">
<div class="container-background"></div>
<div class="content">
Yay, happy content!
</div>
</div>

Then make the '.container-background' positioned absolutely to cover the parent element. At this point you'll be able to adjust the opacity of it without affecting the opacity of the content inside '.container'.

.container {
position: relative;
}
.container .container-background {
position: absolute;
top: 0;
right: 0;
bottom: 0;
left: 0;
background: url(background.png);
opacity: 0.5;
}
.container .content {
position: relative;
z-index: 1;
}

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Try this trick .. use css shadow with (inset) option and make the deep 200px for example

Code:

box-shadow: inset 0px 0px 277px 3px #4c3f37;

.

Also for all browsers:

-moz-box-shadow: inset 0px 0px 47px 3px #4c3f37;
-webkit-box-shadow: inset 0px 0px 47px 3px #4c3f37;
box-shadow: inset 0px 0px 277px 3px #4c3f37;

and increase number to make fill your box :)

Enjoy!

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.class {
/* Fallback for web browsers that doesn't support RGBa */
background: rgb(0, 0, 0);
/* RGBa with 0.6 opacity */
background: rgba(0, 0, 0, 0.6);
}

Copied from: http://robertnyman.com/2010/01/11/css-background-transparency-without-affecting-child-elements-through-rgba-and-filters/

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#id {
position: relative;
opacity: 0.99;
}


#id::before {
content: "";
position: absolute;
width: 100%;
height: 100%;
z-index: -1;
background: url('image.png');
opacity: 0.3;
}

Hack with opacity 0.99 (less than 1) creates z-index context so you can not worry about global z-index values. (Try to remove it and see what happens in the next demo where parent wrapper has positive z-index.)
If your element already has z-index, then you don't need this hack.

Demo.

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Here is another approach to setup gradient and stransparency with CSS. You need to play arround with the parameters a bit though.

background-image: -webkit-gradient(linear, left top, left bottom, color-stop(0%, rgba(0, 0, 0, 0)), color-stop(100%, transparent)),url("gears.jpg"); /* Chrome,Safari4+ */
background-image: -webkit-linear-gradient(top, transparent, transparent),url("gears.jpg"); /* Chrome10+,Safari5.1+ */
background-image:    -moz-linear-gradient(top, transparent, transparent),url("gears.jpg"); /* FF3.6+ */
background-image:     -ms-linear-gradient(top, transparent, transparent),url("gears.jpg"); /* IE10+ */
background-image:      -o-linear-gradient(top, transparent, transparent),url("gears.jpg"); /* Opera 11.10+ */
background-image:         linear-gradient(to bottom, transparent, transparent),url("gears.jpg"); /* W3C */

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body {
' css code that goes in your body'
}


body::after {
background: url(yourfilename.jpg);
content: "";
opacity: 0.6;
position: fixed;
top: 0;
bottom: 0;
right: 0;
left: 0;
z-index: -1;
width:auto;
height: 100%;
}

So to say its the body::after you are looking for. This way the code for your body is not changed or altered only the background where you can make changes where necessary.

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Try this

<div style="background: linear-gradient( rgba(0, 0, 0, 0.7), rgba(0, 0, 0, 0.7) ), url(/image.png);background-repeat: no-repeat;  background-position: center;"> </div>

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I use it, I tested it on a white background, but it can be matched to the background color, especially if using css var:

background: #ececec99;
background-blend-mode: lighten;
background-image: url(images/background-1.jpg);
background-repeat: no-repeat;
background-size: cover;
background-position: center;

It's important to note that I only checked this in the Chrome browser.

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To set the opacity of a background image, you just need to add an opaque image as first image in the background-image set.

Explanation:

The gradient function is creating an image from a color
The rgba function is creating a color that accepts opacity as parameter (ie alpha parameters)
alpha = 1 - opacity of white
Therefore by combining them, you can create an opaque image.

For instance, you can add an opacity of 0.3 by adding the following image linear-gradient(to right, rgba(255,255,255, 0.7) 0 100%) in the set of background-image

Example for an opacity of 0.3

body{
background-image: linear-gradient(to right, rgba(255,255,255, 0.7) 0 100%), url(https://images.unsplash.com/photo-1497294815431-9365093b7331?ixid=MnwxMjA3fDB8MHxwaG90by1wYWdlfHx8fGVufDB8fHx8&ixlib=rb-1.2.1&auto=format&fit=crop&w=1950&q=80);
background-size: cover;
}

Enjoy !

Credits

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You can use a hack to achieve a filter effect. some users mentioned before but none of their answers worked for me except this solution

#item_with_background {
background: rgb(filter_color) url(...)
}


#item_with_background > * {
position: relative;
z-index: 1; // this may cause other problems if you have other elements with higher than 1 z-index. so use with caution.
}


#item_with_background::before {
content: ' ';
position: absolute;
top: 0;
bottom: 0;
left: 0;
right: 0;
background: rgba(filter_color, 0.9);
width: 100%;
height: 100%;
z-index: 0;
}

Here is a working example