Digital TV pictures need a good strong signal to paint a picture - if the signal is weak bits may be missing and the processing electronics don't know what to do with it so you can get intermittent freezing of the image and sometimes no picture at all.
Analogue tuners are less demanding and the TV will paint the screen with whatever it can pick up - you will have seen fuzzy pictures with interference from time to time.
If you suffer freezing or pixilated DTV pictures it will more than likely be caused by a broken or weak signal - look to your connections first then the roof aerial.
Peccavi, March 2010
