One for the experts here.

Firstly I'm not sure exactly how progressive scan works. My understanding is that it somehow "unpicks" the 3:2 pulldown on NTSC DVD material and shows them in proper 24fps. How does it deal with PAL material?


Secondly, I have a DVD player which boasts progressive output (the Sony 910 recorder). It has HDMI and component output. I have a Plasma TV with HDMI and component input. I understand that progressive signals, like HD signals, can only be sent via component, DVI or HDMI. However, my Sony manual says that the player can only output progressive signals through the Component output and not, apparently, through the HDMI.

So in order to see the benefit (such as it is) of progressive scan on my player, do I have to connect it up via component rather than via HDMI - because HDMI in all other respects would seem to be the best bet.

thks in advance

Well this is, as you say, slightly complex. the first thing to do is not to worry about the 3:2 pulldown that is done to allow NTSC to show 24 fps movies at 30fps (60 interlaced frames). I once did the maths on this but I won't bore you.

The difference between interlaced and progressive is to take those 60 interlaced half frames (50 in Europe) and turn them into 30 (25) full frames.

This is a non trivial excercise - the person whose name is synonimous with the technology Mr Farojuda (not sure on the spelling) recently at a conference after he sold his company admited it was an impossible task

Creating a single unified frame is fine but the problem is that in the 60th or 50th of a second between each field things have moved and so the software that "de-interlaces" has to guess where the image would have been if there was only one frame being generated.

Surfice it to say that a good expensive de-interlacer should do a better job that a cheap one.


The output on the HDMI will either be 720p (p for progrssive) or 1080i (i for interlaced) so it rather depends on how you have configured the output of your DVD player as to if the output is progressive or interlaced.

Assuming you have TV whose native resolution is around 720p then you probable want to output in that format.

If the Sony manual says the HDMI output is not progressive, that probably means it just sends the unprocessed digital signal from the DVD to the HDMI port - which would mean it was 576i.

My TV has 1024x768 resoultion.

The HDMI output has 4 options:

Auto
720p
1080i
576p

I watched a R1 NTSC DVD yesterday on AUTO and although it looked great I thought I could detect the 3:2 pulldown giveaway juddering on pans.

That's normal.

A good deinterlacer detects the 3 fields, 2 fields sequence from region 1 DVDs and converts it to 3 frames, 2 frames progressive. The frame rate is still 60 Hz after deinterlacing. The only way to avoid juddering on horizontal pans would be if your TV had a 72 Hz mode (3 x 24fps).

3:2 progressive looks a lot better than 3:2 interlaced.

That's not correct. Progressive outputs carry 50 full frames per second.


That's true when you have an interlaced source, where you do need to generate 50 different frames per second.

However, films are progressive. They'll be stored at 25 progressive frames per second on disc. It's trivial to output this as 50 interlaced fields (basically half the information in each), or as 50 progressive frames (basically each frame, sent twice).

It should be apparent that, for film content, display on a device which requires progressive frames, it shouldn't matter at all whether the connection is interlaced - the original 25 progressive frames can easily be derived from each - either by dropping every other frame, or by combining pairs of fields. Unlike the Americans, we don't suffer 3-2 pulldown, so this task really is trivial.

Which means that, for film content, in PAL land, progressive scan outputs are a complete waste of time - unless your display device is spectacularly stupid.

Cheers,
David.

Sadly, in the HDTV world nearly all displays are 'spectacularly stupid'.

Deinterlacing 1080i to 1080p involves a lot more horsepower than SD. The cheap solution? Treat every 1080i field as if it were a 540p progressive frame, and scale it to the display's native resolution.

It is almost impossible to find a display on sale at the moment that deinterlaces 1080i correctly.

Progressive is only an issue for 30 fps NTSC from film 24fps source.

Hence USA HDTV is 720p, a good improvement on 480lines

In Europe Interlace is not an issue. So to be able to have MUCH higher definition (576 lines to 720 lines is not enough of a step), the "entry level" is 1080 lines.

It is interlaced for the same reason that NTSC/ 525 line , 405 line, 819 line and 625 line were, to halve the maximum scanning frequency.

If it is film or PAL then 576 line interlace unless it is HD.

If it is NTSC (not HD) then 480 progressive is best.

720p and 1080i since they are not exact multiples of 480 or 576 should only be used for HD.

There is a "Gotcha". Many so called HD Ready TVs while supporting NTSC and PAL normal resolution only support USA 720p resolution natively. The 1080i support has artifacts as the image is rescaled to 720 lines

Almost all Euro HD Satellite will be 1080. About 20 channels are running now in 1080i.

You don't want to de-interlace 1080i

How exactly is interlace "not an issue" in Europe? You have no choice but to de-interlace 1080i to display it on a progressive output device.

That's called "bob"ing. http://www.100fps.com/

However, if the material is a film source, it's even cheaper (requires even less processing) just to stitch ("weave") the two interlaced fields together back into one frame. There's a problem though...


I can well believe it. The fly in the ointment is that, to treat 1080i content as 1080p and weave it back together, you need to detect when this would be appropriate (i.e. when the content is film). If you weave video content back together, it looks terrible, with obvious interlacing artefacts.

So the easy option is to bob all the content (treat it as 540p, if you like). This makes video look OK (though it could be better), and makes film content look softer than it should - but it avoids the hideous artefacts that could be introduced by weaving video.

Maybe the EBU is right after all (720p is the way to go for now), or maybe we all need to buy external deinterlacers! Not that many displays accept 1080p50!

Cheers,
David.

The issue is that Flat panel displays are Natively Progressive... thus they have to be fed with Progressive signal.

If the input is 1080 i then the home equipment has to do the conversion -
which is at everyones STB ( cheap and nasty!) - if the input is 720P then very little has to be done in everyones STB. Just one exepnsive box at teh coder
Also P signals code more efficiently so it may be that Programmes are made 1080i because that looks like TV - and HD is always trasnmitted 720P as this is the most efficent way to code
- and has the SAME vertical resolution as 1080i (Kell Factor) .

Films being fundermentally P may be transmitted "i" which could improve resolution (perhaps!)

You have to remember that interlace is Analogue compression!!! - so why do we need it in a digital world.

Interesingly, it can help, even with digital compression...

http://svt.se/content/1/c6/41/21/70/...exga_final.pdf

The conclusion in that document is that we should go with 720p - but if you look at the actual results, 1080i looked better for most content at most bitrates.

Maybe newer video codecs (e.g. MPEG-4) will close the gap.

Cheers,
David.

The conversion won't be done by the STB. The STB will output native 720p and 1080i and the TV will do the scaling/deinterlacing. There may possibly be an option on Sky's and other HD boxes to convert 1080i to 720p, but you can be sure it will be done badly using the cheap field bob algorithm used by all current HD displays.

I thought the whole point of having a "progressive" option, was that it "unpicked" the extra field from 24fps which had been converted to 30fps NTSC via the pulldown method, thus giving you 24fps?

Nope. DVD players with an "NTSC" progressive scan output will output 60 full frames per second. The 3-2 sequence will be maintained. Pans will still "judder".

There are TVs which detect the 3-2 sequence and go into 72fps mode, as already mentioned.

Cheers,
David.

Take a look at this article, which compares the original progressive frames from It's a Wonderful Life to the 30fps interlaced NTSC DVD.

Progressive scanning does not eliminate judder but it does get rid of the nasty combing effect caused by interlacing fields from different film frames.