[cheekyangus]

The resolution of Standard Definition varies.

Main channels, like the PSBs, tend to be 720x576 or 704x576.

Smaller channels, even from big broadcasters, can be 544x576.

Some have their main channel on 720x576 and +1 version on 544x576.

And not all channels of the same resolution are equal either. I've seen some 544x576 channels that have much better picture than other ones. I'm no expert, but I suspect some of this is that they use better encoders. There's multiple factors at play, not just encoders.