95

Related to How do I give text or an image a transparent background using CSS?, but slightly different.

I'd like to know if it's possible to change the alpha value of a background image, rather than just the colour. Obviously I can just save the image with different alpha values, but I'd like to be able to adjust the alpha dynamically.

So far the best I've got is:

<div style="position: relative;">
    <div style="position: absolute; left: 0px; right: 0px; top: 0px; bottom: 0px;
                      background-image: url(...); opacity: 0.5;"></div>
    <div style="position: relative; z-index: 1;">
        <!-- Rest of content here -->
    </div>
</div>

It works, but it's bulky and ugly, and messes things up in more complicated layouts.

Community
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Niet the Dark Absol
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13 Answers13

47

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 ? :)

Gabriele Petrioli
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    Looks pretty nice to me in FF5, nice job. I completely forgot that pseudo elements have the `url` property, I tried by using `background` and couldn't solve the the z-index issues (content beneath). – Wesley Murch Jul 31 '11 at 19:27
  • Answer appreciated, but considering how poorly Firefox performs with other things (memory leaks all over the place, horrible lag in JS, it's almost as slow as IE6, certainly slower than IE7...) I will be looking for a more cross-browser solution. – Niet the Dark Absol Jul 31 '11 at 22:36
  • @WesleyMurch, may I request you to have a look at a css , jquery question on a different topic at http://stackoverflow.com/questions/14137378/div-above-another-div-but-should-scroll-beneath-the-later-one – Istiaque Ahmed Jan 04 '13 at 06:40
22
.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/

Andy.Diaz
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18

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.

DanMan
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    One caveat to the multiple-backgrounds technique is that the opacities will multiply rather than add together. If you overlay two 50% opacity images, the result will be one 75% opacity image. Add another one, the opacity jumps to 87.5%, another one 93.75%. Mathematically, the total opacity approaches, but never actually reaches 100%. In practice though, thanks to rounding, you would need a stack of 9 to bring a 50% opacity image to 100%. – Iain Fraser Mar 14 '13 at 01:07
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    For those mathematically inclined, here's how you work out what adding another semi-transparent image to a stack will do to the overall opacity: `stacked_opacity = current_opacity+((1-current_opacity)*single_opacity)` So if our current opacity is 0.25, adding another image will give us 0.4375, thus; `0.25+((1-0.25)*0.25) = 0.4375` Adding another will give us 0.578125, thus; `0.4375+((1-0.4375)*0.25) = 0.578125` – Iain Fraser Mar 14 '13 at 01:20
17

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!

Saud Alfadhli
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    this does not work for what OP wants but fills my requirements perfectly, thanks!! – RozzA Aug 19 '13 at 23:10
  • @rozzA the OP didn't state there was another image in the background. In fact he only wanted to know whether it's possible to change the background's opacity, and answered: "NO". This is a nice approach :) but not different to adding a new background with rgba transparency. – sergio Feb 27 '14 at 19:15
17

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>
gerardnico
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JM Causing
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  • Would love to see the linear-gradient remain in position, even if you change the background-position. – klewis Feb 04 '20 at 14:10
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    Yaaay! That's de only true one!! css based only and without any other html tags involved. – Despertaweb Mar 15 '21 at 15:09
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    Woooo! It took hours of googling to find this--thank you so much for posting. I wanted a white overlay/transparency instead of black so I changed `rgba(0, 0, 0, 0.7)` to `rgba(255, 255, 255, 0.7)`. And it only affects the background instead of the entire element ^__^ – velkoon May 26 '21 at 21:14
11

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

vsync
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gerardnico
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    it's not opacity, it's simply overlaying a white semi-transparent color on top of the image. This is only useful when the background color behind the image is solid – vsync Jun 05 '21 at 19:50
9

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;
}
Alex K
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  • Isn't this exactly the same as the "hack" I used in the question? – Niet the Dark Absol Feb 22 '13 at 19:59
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    Hmm... I suppose, but I'm not understanding what's not working for you. I use this method and it works great. – Alex K Feb 28 '13 at 21:35
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    IT IS EXACTLY as your hack, but because you are reluctant to provide an example and by your comment "@Eric: I'm not referring to any specific case with this, I'm trying to find a general solution to the problem" you seem clear on what you want is not a hack or a workaround that might work for certain scenarios (though you are providing one), but rather the plain answer whether it's possible or not. **So the correct answer is "NO, it is not possible as of current CSS specifications".** Your problems seem to be some layouts result "complicated" for you. This answer de-complicates it for you. – sergio Feb 27 '14 at 19:00
  • I meant exactly as the OP example. – sergio Feb 27 '14 at 19:17
1
#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.

user
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  • @bjb568 Yeah, that was my first thought. But it doesn't really work as translucent background, acting as translucent foreground instead. Try to add an image inside of block or change text color to background color (white) and you'll see. – user Feb 03 '14 at 08:09
  • @bjb568 Yup, in your example you can see the should-be-background over the inner image. Try to increase opacity of the "background" element, and you'll see how inner image fades away. – user Feb 04 '14 at 01:10
  • @bjb568 Have you ever wondered *why* you had to add `no-repeat`? You think your version is ok because the element is fixed size that is equal to the bg image size, and because you don't have any parent element with background (background-color would suffice). – user Feb 04 '14 at 10:55
  • @bjb568 I gave thorough example. If you think it has redundancy, start *with it* and try to remove anything. You'll see that each parameter has it's place. If you think you've found an *another* technique, please post it as *another* answer. – user Feb 04 '14 at 11:22
  • I have wondered. I can also do it without weird hacks. No-repeat is for... it not repeating. Ok, fine. Another answer, then. – bjb568 Feb 04 '14 at 15:34
  • @bjb568 In your last demo the pseudo element is positioned to be `` background, not the element's background, that's why it is repeating. – user Feb 04 '14 at 16:56
1

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 */
Stanislav
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1

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.

איש נחמד
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1

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

Pars
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1

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.

Cokegod
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  • This is the straighter answer, if we forget the OP provided an "alternative", but consider he commented later that he "doesn't want to provide an example" (to provide an alternative). So considering he just wants the answer, here it is :) – sergio Feb 27 '14 at 19:20
-1
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.

Ali Silva
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