1080i vs. 720p

[ppppenguin]

As old_tv_nut has said, there are so many other variables in the transmission chain it's almost impossible to compare the relative performance of 720p and 1080i in the home.

Interlace was once a wonderful system to reduce bandwidth but it's now just a curse. It's difficult if not impossible to undo it accurately for progressive displays. All flat panel displays are progressive. The best one can say is that receivers have got better, the days of the 2 field splitting apart to give comb shpaed edges on moving objects have largely gone.

[rant] Another curse is the old USA frame rates of 29.97Hz etc. Except they don't affect the home user, only programme makers/distributors. First introduced to cope with NTSC colour (they either had to move the sound subcarrier or frame/line rate to make it work OK) it was a valid choice at the time. That was before timecode. It's been a total PITA ever since, as timecode has to be frigged to make it work with these frame rates. (I'm in a 50Hz country where everything works just fine - I just happen to design kit that has to cope with all standards in the studio.

When HD came in why on earth were the 29.97 etc standards retained? If you needed to re-use old material in a true 30Hz/60Hz standard environment you just played it in 0.1% fast. The madness has been retained in the 4K era, where the SMPTE standards documents still allow for these wretched frame rates. [/rant]

[Adlershof]

Originally Posted by ppppenguin

Interlace was once a wonderful system to reduce bandwidth but it's now just a curse. It's difficult if not impossible to undo it accurately for progressive displays.

And for this reason public broadcasters in Germany have abandoned production in 720p, in favour of 1080i which they then convert to 720p...

Thus the mentioned discussion.

[andy]

Originally Posted by ppppenguin

...
When HD came in why on earth were the 29.97 etc standards retained? If you needed to re-use old material in a true 30Hz/60Hz standard environment you just played it in 0.1% fast. The madness has been retained in the 4K era, where the SMPTE standards documents still allow for these wretched frame rates. [/rant]

I believe the main reason they don't do that is because of the audio, and for compatibility when editing. You can't just playback digital audio off speed without creating problems, and resampling would be a nightmare (particularly for DD and dts). It would also cause problems when editing since you can't easily make a VCR or other old source play faster.

[old_tv_nut]

Digital came in to use piecemeal with islands of digital processing in essentially analog facilities. The digital gear had to mesh with NTSC rates for a long time.

[ppppenguin]

Originally Posted by andy

I believe the main reason they don't do that is because of the audio, and for compatibility when editing. You can't just playback digital audio off speed without creating problems, and resampling would be a nightmare (particularly for DD and dts). It would also cause problems when editing since you can't easily make a VCR or other old source play faster.

Changing digital audio data rate is routine and commonplace. In dedicated gearbox chips, in software or in programmable logic. The ratio between input and output sampling frequencies can be arbitrary, it doesn't have to be a simple x/y ratio.

For older sources at 59.94Hz you ingest them into your digital editing system and replay them at 60Hz. If you need to transmit 60Hz programmes at 59.94Hz for compatibilty with with legacy NTSC systems then digital playoout systems can do this too.

old_tv_nut's comment about digital islands is true. But for quite a few years production and editing has been entirely digital and computer based. Legacy material on tape is ingested before being used and can be readily converted to whatever standard is required.

[andy]

Originally Posted by ppppenguin

Changing digital audio data rate is routine and commonplace. In dedicated gearbox chips, in software or in programmable logic. The ratio between input and output sampling frequencies can be arbitrary, it doesn't have to be a simple x/y ratio.

For older sources at 59.94Hz you ingest them into your digital editing system and replay them at 60Hz. If you need to transmit 60Hz programmes at 59.94Hz for compatibilty with with legacy NTSC systems then digital playoout systems can do this too.

old_tv_nut's comment about digital islands is true. But for quite a few years production and editing has been entirely digital and computer based. Legacy material on tape is ingested before being used and can be readily converted to whatever standard is required.

All true now, but not back in the early days of HD when the standards were set. Old and new equipment had to run at the same frame rate to be compatible.

Also, how would they have broadcast HD in 60Hz, while simulcasting it in NTSC 59.94Hz? Our digital OTA adapter boxes would be a problem.

I'm curious to see what happens when you do try to generate NTSC at 60Hz. I'm guessing you end up with a lot more interaction between the chroma and luma.

[NewVista]

Originally Posted by Adlershof

..The point is that all ARD studio outputs and internal feeds are 1080i. Only in the last stage they convert their video to 720p, thus combining the disadvantages of both formats.

You are right to suspect that you're getting ripped-off, because 1080 is patently better than 720 - especially when displayed at 4k. And interlace is not a problem because today, better broadcast cameras & telecine now output PsF which nicely complements 2k/4k progressive home displays.

[ppppenguin]

Originally Posted by andy

All true now, but not back in the early days of HD when the standards were set. Old and new equipment had to run at the same frame rate to be compatible.

Also, how would they have broadcast HD in 60Hz, while simulcasting it in NTSC 59.94Hz? Our digital OTA adapter boxes would be a problem.

I'm curious to see what happens when you do try to generate NTSC at 60Hz. I'm guessing you end up with a lot more interaction between the chroma and luma.

In the early days of HD I suppose there was some reason for using 59.94Hz. By the time they got to 1080/60p (uses 3GHz SDI in the studio) the production chain was all digital and largely tapeless. Hard to see any reason for 59.94.

As I've said before, there's no problem trasnmitting at 59.94Hz, even if the material was made at 60Hz. NTSC at 60Hz doesn't (or shouldn't) exist.

[BBTV]

Y'all would be literally sick if you ever had the chance to compare the garbage that comes out of your cable box (any cable box) to the signal leaving a broadcast truck or studio. If we could all see that quality, there would have been no need for the great failed 3D experiment. It is that good.

I usually respond to questions such as which format is better, with .... it was all better before cable I could probably make a case that if enhanced NTSC had been allowed to live, it might have rivalled or surpassed the digital formats as well. Of course, digital offers a lot of other features that analog never could but ...... hey, I'm old. What can I say ??

Oh yea ... your EYEBALLS are actually analog :-D But I digress .....

I thought it would be better with DirecTV or Dish, eliminating the land based compression in the various spots where that happens along the way, but sadly, no. The dirty little secret of digital TV is that unless you are looking at in "native" format, it's going through at least one, and usually many, format conversions, not the least of which happens in your actual display. And cable box. And And And. Each one of these steps has some penalty to quality.

Phooey!

[wa2ise]

Originally Posted by BBTV

... I could probably make a case that if enhanced NTSC had been allowed to live, it might have rivalled or surpassed the digital formats as well.

Back around 1988, when I worked for Philips Labs we were developing an enhanced NTSC scheme that would use a 2nd TV channel to provide side panel area for a 5:3 aspect ration screen, and additional scan lines to provide real progressive scan. It sorta worked, looked decent under clean lab conditions, but surely would look awful after noise and ghosts got into it. The side panels would have different ghosts and noise than the regular NTSC channel. It was a lame system...

[Chip Chester]

BBTV wrote: "I thought it would be better with DirecTV or Dish..."
In part of my pro video work, I've had to monitor various differences between terrestrial over-the-air broadcasts (probably the best signal a consumer can get except for file-based) and DirecTV. The big hint is: It takes 9 seconds for a local's signal to make it to, thru, and up and down (2x round trips) from the local to DirecTV's receiver. Only a second of that is spent in-transit to and from satellites. The rest is bandwidth-preserving squishing to a hopefully-not-to-apparent degraded signal to squeeze in a few more pay-per-view movie channels. Even with spot beams for locals, the quality is not there when compared to OTA. Granted, not all is sweetness and light within the TV station either, but if there's no intermediate studio-transmitter link, what comes out the big stick is better than most other options.