Vibration on braking: New discs needed?

I know there's a couple of other threads on this which seem to suggest there'll be some deposit on the disc itself like this:

Before-Small.jpg

However, my front discs look clean and I'm getting a juddering coming through the wheel on braking.
Could they still be 'warped'? Should I get them 'skimmed', or sand them down with something...or just get new ones all together?

Thanks! Martin.
 
Clean them first, then try re-bedding them in (google for some rough guides on how to do it properly), if not they can be warped it's just not as common as people think. I had some that I managed to warp but it took getting them so hot the disc faces turned a bright blue.