How to make centre cropped image responsive?

Question

Based on an existing answer, I have managed to centre crop an image. I am having trouble making the centre cropped image responsive, though.

Question

When I reduce the size of the web browser window, the centre cropped image does not scale down nicely. Instead, it maintains it's fixed height and width and spills out of the view-port. The problem is perhaps demonstrated more clearly with a Fiddle.

How can I make the centre cropped image scale down nicely? Ideally the centre cropped image will scale down nicely while still being cropped and maintaining a similar aspect ratio.

.centered-container {
  max-width: 960px;
  margin: auto;
}
.center-cropped-img {
  width: 640px;
  height: 360px;
  overflow: hidden;
  margin: 10px auto;
  border: 1px red solid;
  position: relative;
}
.center-cropped-img img {
  position: absolute;
  left: -100%;
  right: -100%;
  top: -100%;
  bottom: -100%;
  margin: auto;
  min-height: 100%;
  min-width: 100%;
}

<div class="centered-container">
  <div class="center-cropped-img">
    <img src="http://i.imgur.com/Ag2ZCgz.png" alt="" />
  </div>
  <div class="center-cropped-img">
    <img src="http://i.imgur.com/BQUgmlB.png" alt="" />
  </div>
</div>

Again, here is a Fiddle that perhaps demonstrates the problem better than in prose.

Answer 1

Read the comments in the code for an explanation.

JSFiddle

HTML

<div class="container">
  <img src="http://i.imgur.com/Ag2ZCgz.png" alt="" />
</div>
<div class="container">
  <img src="http://i.imgur.com/BQUgmlB.png" alt="" /> 
</div>

CSS

/*some basic markup for a flexible container to crop the image*/
.container {
    width: 80%;
    border: 3px red double;
    margin: 50px auto;
    padding:0;
    overflow: hidden;/*do not show image that is overflowing*/
    background-color: yellow;
}
.container img {
    display: block;
    width: 200%;/** (1 / part of the total image width you want shown)*100% In this example you want to show 50% of the image-width**/
    margin-left:-50%;/*move the image to the left, removing that content from view (and making content on the right appear). -0% will show the left side of the image. The negative value of the defined width in the rule before this one + 100% will show you the right side of the image. I guess you can figure the rest out by changing this value.*/
    margin-top: -25%;/*changing the top and bottom values is a bit of a pain. After some trial and error (in google chrome) it appears they are based on the width of the image container, not the height (how unusual is that!!!). So putting -100% in this value would (re)move the image up by the px value of the width of the #container div. If you are using css sprites you should avoid setting this value other than 0%.
Alternatively do some math on the original dimensions of the image:    -(vertical pixels you want off the image)/(image width)* 100%    should work for pixel precision).
The good news is that the image scales with the #container div. So the image grows and shrinks with the container showing the exact same part of the image (and not showing more/less content).*/
    margin-bottom:-25%;/*(re)move some of the bottom part of the image. See margin-top for more (works identical)*/
}