example.sass

img
  // graycity($gray, $opacity)
  @include graycity(0.5, 0.7)

graycity.sass

@mixin graycity($gray: 0.7, $opacity: 0.8)
  opacity: $opacity
  -ms-filter: "progid:DXImageTransform.Microsoft.BasicImage(grayscale=$gray)"
  filter: url('data:image/svg+xml;utf8,<svg xmlns="http://www.w3.org/2000/svg"><filter id="grayscale"><feColorMatrix type="matrix" values="0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0 0 0 1 0"/></filter></svg>#grayscale')
  filter: gray($gray)
  -webkit-filter: grayscale($gray)
  &:hover
    opacity: 1
    filter: none
    -ms-filter: "progid:DXImageTransform.Microsoft.BasicImage(grayscale=0)"
    -webkit-filter: grayscale(0)

licence.md

Lizenz

Das Mixin graycity steht unter der "MIT License (MIT)"
This mixin graycity is published under the "MIT License (MIT)"
http://www.opensource.org/licenses/mit-license.php