100% width background image with an 'auto' height

Question

I'm currently working on a mobile landing page for a company. It's a really basic layout but below the header there's an image of a product which will always be 100% width (the design shows it always going from edge to edge). Depending on the width of the screen the height of the image will obviously adjust accordingly. I originally did this with an img (with a CSS width of 100%) and it worked great but I've realised that I'd like to use media queries to serve different images based on different resolutions - let's say a small, medium and a large version of the same image, for example. I know you can't change the img src with CSS so I figured I should be using a CSS background for the image as opposed to an img tag in the HTML.

I can't seem to get this working properly as the div with the background image needs both a width and a height to show the background. I can obviously use 'width: 100%' but what do I use for the height? I can put a random fixed height like 150px and then I can see the top 150px of the image but this isn't the solution as there isn't a fixed height. I had a play and found that once there is a height (tested with 150px) I can use 'background-size: 100%' to fit the image in the div correctly. I can use the more recent CSS3 for this project as it's aimed solely at mobile.

I've added a rough example below. Please excuse the inline styles but I wanted to give a basic example to try and make my question a little clearer.

<div id="image-container">
    <div id="image" style="background: url(image.jpg) no-repeat; width: 100%; height: 150px; background-size: 100%;"></div>
</div>

Do I maybe have to give the container div a percentage height based on the whole page or am I looking at this completely wrong?

Also, do you think CSS backgrounds are the best way to do this? Maybe there's a technique which serves different img tags based on device/screen width. The general idea is that the landing page template will be used numerous times with different product images so I need to make sure I develop this the best way possible.

I apologise is this is a little long-winded but I'm back and forth from this project to the next so I'd like to get this little thing done.

Answer 1

Instead of using background-image you can use img directly and to get the image to spread all the width of the viewport try using max-width:100%;.

Please remember; don't apply any padding or margin to your main container div as they will increase the total width of the container. Using this rule, you can have a image width equal to the width of the browser and the height will also change according to the aspect ratio.

Edit: Changing the image on different size of the window

$(window).resize(function(){
  var windowWidth = $(window).width();
  var imgSrc = $('#image');
  if(windowWidth <= 400){           
    imgSrc.attr('src','http://cdn.sstatic.net/Sites/stackoverflow/company/img/logos/so/so-icon.png?v=c78bd457575a');
  }
  else if(windowWidth > 400){
    imgSrc.attr('src','https://i.sstatic.net/oURrw.png');
  }
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="image-container">
  <img id="image" src="http://cdn.sstatic.net/Sites/stackoverflow/company/img/logos/so/so-icon.png?v=c78bd457575a" alt=""/>
</div>

In this way you change your image in different size of the browser.