CSS Only solution to turn my images colored when hovered

well , what i actually wanted to acheive is turn all my images in the gallery grey and when hovered back to colored , exactly as the following solution i found on the web .

Link Here

can somebody really explain to me , what does ? also in the HTML i see attributes like k1="0" k2="1" k3="0" k4="0" what are they ? in the CSS i see the below confusing , mind tangling bit of code :

    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");

What does that mean too ? do i need a SVG or a simple and humble do the trick ? also do i need all of this for a simple greyscale to colored hover effect ??

Thanks and regards .

Gautam.