Lately I have been taking a lot of pictures of my daughter and edit them using Adobe Light room.
Every time I find a photo that have a bit of noise in it i make sure to reduce the noise using light room, the resulting picture looks perfect when viewed in any picture viewer ( windows default, Picassa ...)
The trouble is when I need to set the same picture as my desktop background. All of a sudden a fine looking picture starts looks grainy on the desktop. I thought I was doing some mistake while editing the photo or could be an issue with my camera. After doing some searching I found that many faced the same issue. Turns out that windows does so due to some performance reason.
The Fix: Re-size your picture according to your desktop resolution. Initially all my pictures coming out of my D7000 camera were around 4900 x 3200 pixels. So my re-sizing them to my desktop resolution of 1600 x 900 and then making it as desktop background solved the issue.