@mixin image-rendering ($mode:optimizeQuality) {

  @if ($mode == optimize-contrast) {
      image-rendering: -moz-crisp-edges;
      image-rendering: -o-crisp-edges;
      image-rendering: -webkit-optimize-contrast;
      image-rendering: optimize-contrast;
  }

  @else {
      image-rendering: $mode;
  }
}

@mixin image-rendering ($mode:auto) {

  @if ($mode == crisp-edges) {
      image-rendering: -moz-crisp-edges;
      image-rendering: -o-crisp-edges;
      image-rendering: -webkit-optimize-contrast;
      image-rendering: crisp-edges;
  }

  @else {
      image-rendering: $mode;
  }
}

Update image-rendering mixing to conform with the last specification.
Update image-rendering mixing to conform with the last specification.

More information at [MDN](https://developer.mozilla.org/en-US/docs/Web/CSS/image-rendering) page.