joys_R_us said:
Interlacing a TV signal has a single purpose: Bandwidth compression
While this method might have been a viable one 60 -70 years ago, nowadays we have powerful computers doing much more intelligent work in compressing signals (e.g. MPEG 4 AVC).
Hence no need for interlacing whatsoever !
Whilst what you say is true for transmission - it isn't quite the same for production - i.e. how you actually make the programmes.
Broadcast video doesn't use compression "in studio" to link items of equipment (as compression introduces both quality loss - and time delays - neither of which are desirable) Small amounts of compression are used in VTRs and Disc Servers (but these are only in the region of 2:1 to 20:1 ish - not the 100+:1 that is used in transmission)
Whilst it may well be quite easy to broadcast 1080/50p at an acceptable quality, using the latest transmission codecs, it is still a non-trivial exercise to actually produce real-TV in this format. HD-SDI is the standard connection system for broadcast cameras, mixers, VTRs, graphics equipment etc. It carries around a max of 1.2Gbps - which is enough for 1080/50i or 60i, or 720/50p or 60p - but nowhere near enough for 1080/50p or 60p - which is the progressive equivalent in motion terms.
It is possible to double-up and use dual-HD SDI connections, and use more VTR compression (or seriously expensive VTRs) - but this just simply isn't practical in a TV environment (say an OB covering a football match)
The bottom line is that for production - the options are pretty much :
1080/24p/25p/30p (low frame rate - film equivalent - no good for sports)
720/50p/60p (high frame rate - progressive - lower horizontal resolution)
1080/50i/60i (high field rate - interlaced - higher horizontal resolution)
Whilst 1080/24-30p seems like a good solution - the low frame rate really isn't good enough. It is good as a film-replacement for drama - but you'd be mad to limit your production systems to it.
720p or 1080i at 50 or 60 are still the only real games in town for running a real transmission system currently.
If you were really keen on future-proofing your system you could conceivably gear up for 1080/50p or 60p transmission (so your encoders and receivers were 1080/50p or 60p compatible) - but currently just feed this with 720p or 1080i source material. However the cost to implement 1080p in domestic receivers is also non-trivial. (You have to remember it is running at twice the uncompressed data rate of 1080i, which itself runs at a higher data rate than 720p)