Retina images mixin for SCSS

_retina.scss

@mixin at2x($image_name, $w: auto, $h: auto, $extention: '.png') {
	background-image: image-url($image_name + $extention);
	$x2img : $image_name + '@2x' + $extention;

	@media 
	all and (-webkit-min-device-pixel-ratio : 1.5),
	all and (-o-min-device-pixel-ratio: 3/2),
	all and (min--moz-device-pixel-ratio: 1.5),
	all and (min-device-pixel-ratio: 1.5) {
		background-image: image-url($x2img);
		background-size: $w $h;
	}
}