View Full Version : 1080i vs. 720p


Adlershof
06-03-2017, 05:44 PM
Any opinions about the pros and cons of these two formats?

I would like to read some in particular from the US, because here in Europe this is almost a matter of religious belief. When introducing HD engineers of German public broadcasters resolutely said that interlaced formats must finally be a thing of the past, defending their decision to use 720p against demands for "full HD", i.e. 1080i.

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.

Chip Chester
06-03-2017, 07:02 PM
Stateside, the mantra is 720p for sports, apparently for its better motion characteristics. Since most content is squeezed down DirecTV/Dish Network satellite, and cable systems, few viewers see anything close to full fidelity of either format. The only real way to get it is by antenna. Or thru streaming video, sometimes. They can do 4K, but various compression artifacts sometimes dilute the experience. Sometimes.

Chip

old_tv_nut
06-03-2017, 10:24 PM
The comparison was more distinct when using a CRT display that scanned in the native format of the capture. It was quite true that sports looked better in 720p (viewers particularly mentioned the difference on basketball games). Mostly-still images, on the other hand, had noticeably better horizontal resolution upon close examination.

Since flat panel displays all are longer persistence than CRTs, and native 1920x1080 flat panels require interlace to progressive conversion of some type, the comparison is muddied these days.

jsowers
06-03-2017, 11:58 PM
Stateside, the mantra is 720p for sports, apparently for its better motion characteristics. Since most content is squeezed down DirecTV/Dish Network satellite, and cable systems, few viewers see anything close to full fidelity of either format. The only real way to get it is by antenna. Or thru streaming video, sometimes. They can do 4K, but various compression artifacts sometimes dilute the experience. Sometimes.

Chip

I'm sitting here watching SNL at 1080i on my "analog cable." No silly box. Just plug the cable into the back of my flat screen TV and auto scan the channels. When I press "info" on the remote, it says 1080i for the local NBC and CBS stations. Other stations say 720p and the regular cable channels 2 through 76 say 480p. So everything isn't digital. My cable provider puts the digital versions of the local stations, and their sub-channels, on a separate tier and the signal is gorgeous and dropout-free. So am I one of the lucky ones?

I dropped Time-Warner after 20+ years when they discontinued analog and went with the local telco's cable TV and have never regretted it for a second. TWC, now Spectrum, still wastes their money sending me something almost every week and I've had two visits from someone trying to get me back. I told him I wouldn't have it even if it were free and slammed the door in his face the first time. The second time I wasn't home, but the sheet he left said I got a free "motem" with their service.

I think I'll keep what I have for as long as I can.

old_tv_nut
06-04-2017, 12:48 AM
There is no analog transmission of 1080i or 720p (high definition) on any media or service anywhere, and never was. You must be watching a digital signal for these.

Chip Chester
06-04-2017, 11:21 AM
All of those display formats are possible in ATSC. And for the tuner to receive 1080i, and moreover say it's 1080i, it has to be an ATSC tuner. 480p confirms it, as NTSC is 480i. (Actually 525i, only 483 of which are visible... but who's counting?) If you're in PAL country, your lineage may be different, but the concept is the same.

But comparison of that show via cable vs. the same show at the same time via antenna will reveal the compression and general monkey business taking place at the cable company front-end that allows enough space on the system to present 82 PPV wrestling and on-demand movie choices and 142 shopping and sports channels in addition to the normal broadcast and cable-box-only offerings. Even though you're not watching them, or ordering them, they still take up room on the cable spectrum that shows up at your house. I call shenanigans. (On BigCable, not you.)

Chip

Robert Grant
06-23-2017, 08:41 AM
There is no analog transmission of 1080i or 720p (high definition) on any media or service anywhere, and never was. You must be watching a digital signal for these.

Technically, Japan did offer analog HDTV service many years ago, using an 1125-line raster to deliver a 1080i image.

jsowers is apparently one of the lucky few in America that still gets open digital cable (unencrypted QAM, or, even more unlikely, ATSC).

The vast majority of CATV systems in the USA encrypt EVERYTHING on their system (with perhaps the sole exception of an analog channel 3 with a slide showing the telephone number to the company's new subscription office). This allows the CATV company to shut a customer off without actually sending a person to unplug a cable on a utility pole, meaning they can layoff several employees who did so.

Electronic M
06-23-2017, 11:48 AM
Here last summer they switched off ~70 analog channels, and replaced it with this encrypted QAM BS. The get a box analog lasted till winter. Now all that is left is encrypted QAM, a FEW locals on ATSC or clear QAM (I forget which) And 1-2 garbage unencrypted QAM channels.

I had at least 4 DVR/DVD-recorders/S-VHS decks hooked to analog cable and could tune, watch and or record 4-10 shows at once on the rig in my room, and I could have my time shifts change channel to grab various shows (important, especially on long vacations)....Now I've got 1 maybe 2-3 channels (if I heist boxes from other rooms) at once, at best, with the same gear (and no way for the timers to change channels) unless I engineer some super complex IR remote based automation project. I would not mind half as much If the basterds did not encrypt their service...I was prepared to get plenty of clear QAM decoder boxes and 'make my own analog cable', and or get some more QAM tuner sticks for my PC and use those as tuner/DVRs....If that ain't enough to burn my ass already the jerks at scrotum cable think in under 1 year they are gunna get away with charging $6 a month a head rent on those 5 "free" hockey phuck boxes....I think I'll we'll end up switching to playstationVue or some combination of that Hulu, Roku, streaming....Their shyte is expensive enough as it is, and they have the gall to change up the hardware to serve me worse, and charge me more for it?...They might do better to simply ask us nicely to leave.

I'm smarter than every scrotum employee whom I've met or who's decisions have affected my service.....Literally I had to explain to the first tech how to run the damn coax he was installing through the walls/vents, that clown did not install an amp as I was sure we needed, and the next installer who came to fix internet/phone dropouts realized the amp was needed to fix that....Two weeks back I had to climb the damn pole....All the little phuck boxes were not getting signal and the big box was lousy (phone &net somehow were okay), with no analog relative signal strength was hard to judge....I first checked the 'splices' on the underground cable that mom's gardening brought back to the surface to find they were fine...checking the amp etc proved things so I went up to try to bypass the line before the splice....When I went up there I found our fitting at the spliter* during a recent replacement of the splitter had been over tightened till the threaded collar on the F connector cracked off the connector...Leaving ONLY the center lead of the coax just barely coupling signal between us and the cable co... :grr: It was not too hard to change the fitting, and I did it safely (a 2 phase 120V + cable pole ain't too dangerous), but having to do it at all ticks me off (once the problem was discovered it was either miss my shows and let them do it or DIY fix and watch my shows).
*There are 2 taps on the proper outdoor cable co hardware on my pole and 3 homes using it...So some enterprising cable guy added a second consumer grade spliter in series with the telco grade one on the pole to add an extra tap....Yeesh!

KentTeffeteller
06-30-2017, 08:38 PM
Add to this the cable companies compressing their feeds which means you don't get real HD either. Satellite from DirecTV and Dish also compress theirs.

centralradio
09-21-2017, 12:16 PM
The cable companies compress the crap out of channels and they look like a crappy webstream video or Youtube video.The artifacts look horrible on a large TV set.I think the analog cable was better at times.

Dave A
09-21-2017, 08:06 PM
Cables keep a few analog slide channels around. One low. One high to help the field techs to adjust the "tilt" on the entire spectrum they are using. The whole spectrum slides down in signal level and the "tilt" gets them back to an even level. Quick and dirty testing.

ChrisW6ATV
01-28-2018, 10:02 PM
Any opinions about the pros and cons of these two formats?
I watch a lot of USA football, and the games are on both 720P and 1080I channels, so I can compare motion performance and other issues easily between the two formats. Most of my watching is with a Windows Media Center digital recorder (DVR), so I also can easily compare slow-motion or freeze-frame images as well.

The result I have found, using flat-panel displays or an LCD front-projection display, is that 720P may have slightly sharper images if viewed in freeze-frame mode, but in actual normal-speed viewing, I never notice any "lag" or "smearing" or other possible problems in games shown in 1080I mode. Nor do I see any "clearer" motion or other improvement in the 720P games. What I truly DO notice, every time in every game, is the mediocre sharpness/clarity of the 720P games versus the nice "pop", "wow, yes, this is high definition" of the 1080I games. Every time. Unfortunately, my favorite team's games (San Francisco 49ers) are mostly shown on the 720P Fox network.

KentTeffeteller
02-08-2018, 09:07 AM
720P works better for sports and motion and also has enough bandwidth for 5.1 surround sound. And works better over the air. 1080i has macroblocking issues sometimes over the air and audio is limited to 2.1 channels over the air due to bandwidth.

ChrisW6ATV
02-10-2018, 02:36 PM
I have watched 1080I shows (and football games) for years that have true Dolby 5.1 surround sound. 720P and 1080I each have about the same basic bit rate (since 720P has about half the resolution but double the frame rate). Actual bit rates and pixellation/macroblocking issues are entirely dependent on the encoding choices made by the program sources and broadcasters, and are not inherently better or worse for either format.

old_tv_nut
02-10-2018, 04:40 PM
It is no longer possible to make a real comparison of 1080i and 720p at home.
1) the greatest degradation of any source is the final bit reduction that the station applies, and how well does the encoder handle images at that bit rate. Since each station does it differently, there is no way to compare 1080i on one station to 720p on another.
2) the second greatest degradation is format conversion - this may happen multiple times from source through distribution to the final station, and also happens in your flat screen TV at home. The anti-aliasing filtering required, plus the conversion from interlace to progressive for the LCD display, completely clouds the issue.

As I have stated on VK before, these two scanning formats, when compared on CRT displays without format conversion, show greater static resolution for 1080i, but sports look better in 720p. In the original tests, naive viewers could easily see the difference. Unfortunately, there is nowhere that this can be viewed anymore except maybe at a studio.

The best of both worlds is obtained by broadcasting 1080p (or higher resolution), which will become the norm with ATSC 3.0.

ppppenguin
02-11-2018, 02:38 AM
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.

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.

Adlershof
02-18-2018, 06:08 PM
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
02-19-2018, 12:22 PM
...
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
02-19-2018, 04:30 PM
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
02-20-2018, 02:15 AM
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
02-20-2018, 11:58 AM
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
02-20-2018, 04:18 PM
..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 (https://en.wikipedia.org/wiki/Progressive_segmented_frame) which nicely complements 2k/4k progressive home displays.

ppppenguin
02-21-2018, 02:10 AM
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
05-12-2018, 03:35 PM
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
05-17-2018, 03:22 PM
... 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
05-17-2018, 06:07 PM
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.