How do you stretch an image to fill a <div> while keeping the image's aspect-ratio?

Question

I need to make this image stretch to the maximum size possible without overflowing it's <div> or skewing the image.

I can't predict the aspect-ratio of the image, so there's no way to know whether to use:
<img src="url" style="width: 100%;">
vs
<img src="url" style="height: 100%;">

I can't use both (i.e. style="width: 100%; height: 100%;") because that will stretch the image to fit the <div>.

The <div> has a size set by percentage of the screen, which is also unpredictable.

Answer 1

That's impossible with just HTML and CSS, or at least wildly exotic and complicated. If you're willing to throw some javascript in, here's a solution using jQuery:

$(function() {
    $(window).resize(function() {
        var $i = $('img#image_to_resize');
        var $c = $img.parent();
        var i_ar = $i.width() / $i.height(), c_ar = $c.width() / $c.height();            
        $i.width(i_ar > c_ar ? $c.width() : $c.height() * (i_ar));
    });
    $(window).resize();
});

That will resize the image so that it will always fit inside the parent element, regardless of it's size. And as it's binded to the $(window).resize() event, when user resizes the window, the image will adjust.

This does not try to center the image in the container, that would be possible but I guess that's not what you're after.

Answer 2

Since you don't know the aspect ratio, you'll have to use some scripting. Here is how I would do it with jQuery

CSS

.container {
 width: 40%;
 height: 40%;
 background: #444;
}
.container img.wide {
 width: 100%;
}
.container img.tall {
 height: 100%;
}

HTML

<div class="container">
 <img src="http://i48.tinypic.com/wrltuc.jpg" />
</div>
<br />
<br />
<div class="container">
 <img src="http://i47.tinypic.com/i1bek8.jpg" />
</div>

Script

$(window).load(function(){
 $('.container').find('img').each(function(){
  var imgClass = (this.width/this.height > 1) ? 'wide' : 'tall';
  $(this).addClass(imgClass);
 })
})