Album covers on rMBP are very low resolution

I've always ignored this problem, so I haven't actually got a clue when it started, I'm afraid, which I realise isn't very unhelpful. I do know that it started after upgrading to Yosemite, though.

The screenshot below shows what the album cover should look like, as it does look like in the 'miniplayer' thing:

The screenshot below what the album cover looks like when looking through all the albums. With a retina display, it's so obvious to me that it's as if it's kicking me in the face.

I just want the Album Covers to be in full resolution so it doesn't look so ugly. If I find it's a bug, that fine, because I know it's not some freak problem that can't be fixed!

Hope I've explained the problem well enough, and I hope somebody can help me out.

I looked for a solution but couldn't even find somebody that had the same problem.

Thanks.