Digital system field/frame rates.

[colly0410]

Been thinking. (Yes I know it'll wear my brain out, & stop laughing those of you thinking "what brain?") In a digital TV system does the field/frame number have to be a sub division of the line number same as in an analog system? Noticed that 1080i & 1080p are used at both 50 & 60 hertz frame rates..

[ppppenguin]

Yes. The hd specs are based on square pixels and the same pixel clock. All 1080 formats have different H blanking periods to make it all work.

[Mike Watterson]

Yes. The hd specs are based on square pixels and the same pixel clock. All 1080 formats have different H blanking periods to make it all work.

Eh?
Most (if not all) Terrestrial HD isn't square  (1440 x 1080 instead of 1920 x1080). Very much HD Satellite has changed from 1920 -> 1440 to match terrestrial output (either to save money or reduce quality).

Maybe I misunderstand what you are saying?

Sadly European HD was crippled to be based on the USA HD based on Japanese Hybrid Analogue 1125 line, to make the data rate about the same. Going from 480 line to 1080 line visible.
The original analogue 60 / 30i and 50 / 25i was two fold:
1) To avoid moving bar (from lighting in studio or PSU on TV set)
2) Interlace takes advantage of the fact we are more sensitive to resolution on a static image, it's a cunning analogue technique to halve the bandwidth.

Digital should have been 48 fps and 96 fps. Certainly progressive only. Interlace is EVIL for format conversions and rescaling and even for digital compression. It's not needed on Digital and a positive problem.

Whatever about 1080 lines in USA (2.25 vertical resolution) based on visible 1125 analogue, surely adopting PC 1200 visible lines would have made more sense in Europe? Or at least 1152 visible. (1296 is 576 x 2.25).

It's ironic that there are now more transmission standards and even HD formats (and very many SD formats) than Analogue had and some are not fit for purpose.

The move to higher resolutions is nonsensical unless you have a 72" screen. What is needed is progressive and higher frame rates. Even if you have a big screen, if the original is scanned from film or shot at 3840 x 2160, and reduced to 1920 x1080 (all Progressive), then it can actually be rescaled on reception for the people that do have larger than 56" screens, indeed up to 72"!
If the screen is 72" rather than 36" because it's 4m away instead of 2m away, then 1920x 1080 is fine, but progressive 96 / 100 / 120 fps will give far more improvement than 4K @ 50 or 60.

Now we have the stupidity that LCD screens on laptops are based on 1920 x 1080 60 fps progressive and we had better computer resolutions for documents, CAD etc 15 years ago!

[ppppenguin]

I'm talking about the standards specified by te SMPTE. There are 2 groups of hd standards. Those with 1920*1080 and with 1280*720. These can be used at any frame rate and for the 1080 line standards also with lnterlace. For studio use all are carried on 1.5ghz serial interface. Except 1080p60 and 1080p50 which use a 3ghz interface. Higher resolution and higher frame rates are defined by later standards. They can use multiple 3ghz links or the new 6 and 12ghz links.

I'm not familiar with what's actually transmitted to homes.

[ppppenguin]

Ought to add that all hd formats are 16:9 aspect ratio and square pixel. Unlike the legacy standard definition formats which have 4:3 aspect but non square pixels.

[Mike Watterson]

Actual transmission is now mostly 1440 x 1080i
Some 720p and 1920x1080 on satellite (but not the main Terrestrial channels)
720i doesn't seem to exist.
The USA also calls 720 x 480p transmission "HD"!

HD is only WS, 16:9. But it's increasingly rare to have square pixel transmission.
SD has very many formats and strangely some allowed on Transmission, not in the DVD spec. It can be WS or 4:3 and WS is often 544 x 576 to save cost (Bandwidth).

Sadly what counts is transmission, and storage not Studio formats specified in a less penny pinching age, though they are USA centric in data rate compatibility.

[ppppenguin]

720 was always progressive. It's also barely HD.

Square pixels are useful for studio processing, much less important for transmission.

Interlace is a PITA but 1080i was the original HD standard, from quite a long time ago, when people still felt interlace was worthwhile. Actually started as 1035i with a longer blanking interval in the same 1125 lines overall. There's still a lot of 1080i infrastructure in TV studios though you wouldn't normally choose to shoot material on it now.

As compression improves the original format matters much less. It's actually easier to compress the data if you start with the highest possible resolution original.

[Mike Watterson]

ppppenguin It's actually easier to compress the data if you start with the highest possible resolution original.

Yes, compression is easier and everything is better if the source is twice the vertical and horizontal resolution.
Interlace is evil. The first step always has to be to convert to progressive, which loses information and creates artefacts. Worst for 24 fps progressive to 30i, which is why "interlace to progressive" filters are usually designed to detect if the source was film and do "inverse telecine" rather than normal interlace to progressive.

The 720p *IS* HD for people used to 480lines, especially interlaced 30 fps from 24fps film! No contest. It's unimpressive compared to decent "PAL region" 576 line DVDs from Film.

As compression improves the original format matters much less.

That's a strange claim. Did you mean that improved standards conversion means original format is less important?  In any case for REALLY stupid production / distribution I would disagree!


Region 1 DVDs are 480 lines. If the source is film, then it's stored as progressive and the DVD player does the 3:2 pull down for interlace which creates the horrid comb artefacts on movement. Unlike VHS where the tape is mastered in evil 3:2. This is why component video and progressive 480p DVD players really took off in USA.  If you have an analogue CRT/TV and only "PAL region" DVDs then there is no point to a progressive DVD player ... but see below!

"PAL" region DVDs are 576 lines and for transfers to film the sound pitch is usually adjusted by 24/25ths so playing the 24 fps at 25fps gives correct pitch. The vertical resolution.

The film used to be scanned at more than twice NTSC/PAL resolution before anti-aliasing and downsampling to 720 x 480 or 720 x 576. Some bluray disks sadly use this master instead of a scan at twice 1920 x 1080 (Minimum is to scan at twice target, there is a good argument now for cameras to run at twice the target resolution, x4 the number of pixels).

The stupidities:
1) "PAL Region" DVDs made by standards conversion of the Region 1 "NTSC 480 30i" video, only acceptable for video source, totally insane for film, as not only is it worse than 30% less resolution than possible, you have a "shimmer" effect especially on horizontal movement.
2) Region One (or Region 0) "NTSC 480 format" DVDs of Film source sold Retail in Europe:  BluRay players unlike DVD are unlikely to be region free, though they will play Region 0. Unless you have a progressive DVD player (or one with decent HDMI built in) and component or BluRay it will look rubbish with comb artefacts.
3) Total madness: Film source mastered as 480i on DVD, poor even on a progressive DVD player with component.

I found when we switched from analogue SD CRT to LCD HD screen that our SCART output DVD player (even in RGB) was much poorer than the Progressive component DVD player even for "PAL Region" DVDs. It outputs at 1440 x 576p or 1440 x 480p if the source is film and properly mastered. For interlaced video originals (a minority of our DVDs) it outputs at 1440 x 576i or 1440 x 480i.

The HD TV obviously has no native interlace mode. It has no per-pixel "Zoom out" mode to suit VHS (NTSC or PAL) better. It's noticeably better with 1080 content and progressive content. Same is true for my VGA CRT running at 1920 x 1080 x 50p from USB DTT stick, DVDs and SD or HD from Satellite (2 x PCI satellite DVB-S2 cards).
576i SD transmissions, interlaced DVDs and all VHS look better on the 28" CRT.

The source isn't anything like irrelevant.

[ppppenguin]

"As compression improves the original format matters much less."

Really meant "modern compression methods can readily handle higher resolution inputs while giving potentially better quality and lower compressed bit rates."

[ppppenguin]

Incidentally, the choice of 16:9 aspect ratio with 1920x1080 pixels predates widescreen computer monitors. Many of these are 16:10 or 1920x1200.