No you don't ONLY get 25 updates per second, you get 50!

The simplest form of de-interlacing while preserving quality is using line doubling ie.

take field 1 (the odd lines of Frame 1) and interpolate (a method similar to how a scaler upscales SD to HD) to fill in the missing even lines. This is your new Frame 1.
take field 2 (the even lines of Frame 1) and interpolate to fill in the missing odd lines. This is your new Frame 2.
take field 3 (the odd lines of Frame 2) and interpolate to fill in the missing even lines. This is new Frame 3.
take field 4 (the even lines of Frame 2) and interpolate to fill in the missing odd lines. This is new Frame 4.

So you get 50 fields = 50 interpolated fields = 50 de-interlaced frames = 50 updates.

What a lovely load of insults but thanks anyway for now backing my original assertion that the data is not 'blasted' onto the screen instantaneously - it is progressively (serially) scanned onto the display elements (although via address selection registers instead of electro-magnetic manipulation of an electron beam).
BTW, I haven't the foggiest where you may have got the idea that I don't understand any of the concepts you felt you needed to expand on or even their relevance to LCD or Plasma display technology. But I'm glad you finally got my point.

Feel free to believe what you like - but the rest of us will live in the real world

Do you have any proof (or even a vague suggestion) of any such thing taking place?.

Presumably you are aware that such an imaginary method would give LESS then SD resolution, and nothing like HD.

Nigel, I already provided proof, more than one decoder on Windows 7 shows framerate doubling for all interlaced material, and if you look here and here you'll see further explanation on how deinterlacing works. This page shows how different levels of deinterlacing affect the picture.

Speak for yourself !
PK is correct but he fails to qualify his assertion sufficiently. His description of a simple line-doubling de-interlacing process is also correct but unlikely to ever be used in practise these days.

If content is recorded at i50 you get 50 fields/time points/changes per second. If this is then transferred to the display using i50 the display will need to update 50 times a second and you effectively get 50 different displayed images (although not full frames) per second.

i50 content can be de-interlaced using a number of different techniques to squash it into p25 or turn it into p50. Either way you are effectively merging two images, from two time points, and some complex image processing is required.

If content is recorded at p25 and transferred to the display at i50 you only get 25 different displayed images per second and de-interlacing is much simpler.

One of the problems for display processors is trying to detect what format the content was originally recorded in to apply the best form of processing.

And has nothing whatsoever to do with TV's or set-top boxes.

100Hz TV's double the frame rate, 50Hz ones don't - it's not difficult to understand.

Of course it does, Microsoft doesn't use any different standards than other manufacturers.


That has nothing to do with what we are talking about, doubling the framerate is a function of most deinterlacing techniques.

Nigel, please stop spouting misinformation as if it's proven fact. These things are clearly well outside your area of expertise, and you're misleading people by pretending that you know what you're talking about.

There are 25 interlaced frames per second = 50 interlaced fields = 50 discrete moments in time.

Deinterlacing that to 25p ("single rate deinterlacing") would throw away half the temporal resolution and it would look stuttery, like 24p or 25p film. Some people do this for pirating interlaced content on the internet, but only a few faulty dirt cheap LCD TVs do this - no half-decent ones do.

Each interlaced frame is used to create two progressive frames, giving 50p ("double rate deinterlacing"). For "top field first" PAL (and all HD), the "missing" information is the even lines (2,4,6) of the first field, and the odd lines (1,3,5) of the second field. If nothing moves, there's no missing information (think about it).

If something moves, you can fill in the missing lines by averaging the lines above+below in the same field (dumb bobbing - simplest form of double rate deinterlacing), or you can use advanced motion compensated recontruction to find the "missing" information where ever it appears in adjacent frames (if it does!).


100Hz or 200Hz has nothing to do with this. This is creating extra frames beyond the 50fps you get by deinterlacing. the thing about 100Hz is you get 100 images per second - not the 50 per second that you claim! The clue is in the name

Cheers,
David.

P.S. I think arguing that plasmas, LCDs etc are not "progressive" is a little silly too. True, they don't scan from top to bottom, but what progressive actually means in "not interlaced". Nothing in the signal processing (except the panel driver technology) cares whether it's scanned top to bottom, or all at once, or at random - the point is that it's not interlaced - each source image consists of one moment in time, rather than two moments interlaced-together line-by-line.

Finally in amongst all the childishness, some useful info comes out.

I would be interested to see the same footage in 720p60, 1080i60 and 1080p60 to see if I can see the difference.

As they don't manufacture TV's or set-top boxes there are no 'standards' in common - and I've no idea what 'standard' you think might apply?.


Yet you are unable to mention a single example of a TV or set-top box that does so? - but instead mention multi-gigahertz processors with multigigabytes of RAM.

Products that de-interlace don't double the frame rate, they de-interlace the image and output 50 frames per second from 50 fields per second. Only (about) half the image changes per 1/50th of a second because it is alternate fields but the output of a de-interlace cannot be 25 frames per second because then the resolution (temporal or visual) of the fields would be lost.

The de-interlacer in most consumer electronics products is far superior to that in most computers because it is a hardware process with specialist DSP elements and is designed purely for image processing. Some consumer electronics inserts more 'enhancement' to the image for my tastes and so people claim the images are sharper but overall CE devices have quite good video processing.

The only thing I have seen CE do badly is PAL decoding into IDTVs, but PAL decoding is difficult to do well in digital and the best mechanisms are patented.

Deinterlacing.


It has nothing to with RAM.



Well that is somewhat the same thing, as 25 frames with 50 fields are input and 50 frames p/s are output.


I think you are a bit behind the times on this Bob, most decent £40+ graphics cards now give very high quality deinterlacing

...but Bob's not trying to sell you a graphics card

Still, hopefully Nigel will believe the Chief Technologist at Humax, even if he doesn't believe us unknowns in this thread!

Cheers,
David.

You missed the point entirely. Non-one has ever said that you can't get 50 fps from a 25fps signal but merely that to do so you have to process the signal to invent extra frames in some way. Bob merely describes one such technique, 100Hz frame doubling is another. The original signal for a full 1920 x 1080 1080i delivers 1920 x 1080 pixels in 1/25 sec. that's it. To get a 1920 x 1080 picture at 50fps you need extra pixels how you do this is not really relevant. So far no-one seems to know which TV's do what with the signal. One thing I do know that is my bluray player delivers 1920 x 1080 pixels progressively to my TV each frame lasting 1/24 second.

No it isn't, that would be a 1080p/25 signal

The whole point about an interlaced signal is that you only get half a frame (a field) at a time.

So a 1080i/50 signal sends 50 fields per second, each being 540 lines. To get a 1080 line progressive signal (as required for full HD LCD/Plasma displays) you need to combine 2 fields together (de-interlace them), there's lots of ways to do this, but the best methods will get (at least) 50 frames per second - otherwise you lose temporal information (assuming the original source is also interlaced).

Of course it can all get quite complicated (the orignal source might have been 25p or a speeded up 24p, or might have been 50i or even 60i) so the best way to de-interlace the picture will be a function of the original input and what compute power is available to throw at it.

Suggest you look around the internet for more information, it's explained a lot better then I could manage!

eg
http://en.wikipedia.org/wiki/Deinterlacing
http://www.hometheaterhifi.com/volum...e-10-2000.html

(There are probably better explanations out there - but these were easy to find )

Precisely - and that word "invent" is the key to it. Let me add a few points for the disbelievers.

It's all about deinterlacers creating an impression of smoothness and an impression of high spatial resolution. But when you dig down beneath the visual impression, no matter how high quality the deinterlacer, the fact remains that on moving scenes including pans, either temporal resolution or spatial resolution, or a combination of the two, will be lost.

You can't create true detail where there was none before, although you may be able to maintain one aspect of it (say temporal resolution) at the expense of another aspect (say spatial resolution). Not even with the most expensive deinterlacer known to man. A good deinterlacer will disguise the trade-off better than a poor one but loss of detail (spatially or temporally) on moving images will still be there, even on a 100, 200 or for that matter 1000 fps TV set.

It's the moving images that are the problem - deinterlacing static scenes and maintaining the spatial detail is a doddle as no temporal detail is required. None of the arguments about whether it's 25 fps or 50 fps when displayed alters that basic point about losing either temporal or spatial detail when deinterlacing moving scenes.

Otherwise, we'd have 1080p/50framesps TV created magically out of 1080i/50 fieldsps broadcasts, which would be a rather wonderful trick!

For crying out loud

1080i - Field A delivered in 1/50 sec 1920 x 540 = 1036800 pixels
- Field B delivered in the next 1/50 sec 1920 x 540 = 1036800 pixels.

combine into 1/25 sec frame = 1036800 x 2 -= 2073600 pixels

1080p25 No fields 1920 x 1080 pixels in one go in 1/25 sec = 2073600 pixels.

1080p25 and 1080i have exactly the same number of pixels, the only difference pixel wise is the interlaced or progressive delivery of the data

1080p50 doubles the pixel transmission rate required.

Absolutely, but that doesn't make 1080p25 and 1080i50 identical, the former has more spatial resolution, the latter more temporal resolution.

I agree that converting a 1080i50 signal to 1080p50 (for display) means you have to create the missing data, but converting to 1080p50 is better than converting to 1080p25 (which would lose temporal data).

In essence the ONLY way to display all the information from an interlaced source on a progressive display is to make up the missing data. So any half-decent de-interlacer will give 50 frames per second from a 1080i source.

(Note that converting a 1080p25 source to 1080p50 by creating the missing intermediate frame is a whole different kettle of fish - you have to guess the entiretly of the missing frame rather than just half of it - and simply displaying it at 25p won't lose any data)

I never said it was the same, the statement that the described 1920 x 1080 pixels in 1/25 sec was 1080p25 was totally wrong. Both interlaced and progressive deliver the same number of pixels at the 25frame/sec frame rate. Interlaced delivers it using two fields each one having half the vertical resolution required for the complete picture.

You make out that interlacing is a good thing, it's not it is a hangover from the way a crt display has to build the picture on screen generating the two fields sequentially each one taking.1/50 sec to complete. Attempting to scan progressively in 1/25 sec top to bottom scan results in the first scan lines vissibly fading before the full frame has been scanned.

As a point of interest most HD-Ready displays wont work with a 1080p signal anyway.
In any case a 1080i transmission with each field derived from a static image (like a frame of film) will deliver eactly the same pixel content whether transmitted 1080i or 1080p25. So where's the difference. The difference is purely decided by the source of the video content

Apologies - misunderstood what you were saying.

No, I don't think interlacing is a good thing - but if you have a 1080i50 signal it is definitely a good thing to de-interlace to 50p not 25p (I don't think we disagree on that either).

Could you clarify what you mean by most HD-Ready displays not working with a 1080p signal? I'd be very surprised if that were to be the case for 1080p25 and 1080p50, though it is certainly true for 1080p24 (I know my panasonic will handle this, which was one of the criteria I used to choose it, wasn't even aware that some HDTV's might not even take a 1080p50 signal, though I guess that could be the case at the cheaper end of the market..)

Certainly in the early days of HD Ready, most (if not all?) HD Ready TV's wouldn't accept 1080P50 signals, and probably not 1080P25/24 either?. You needed a Full HD set to do that, and most of those probably wouldn't accept 1080P24 either.

Eventually a few HD Ready sets appeared which would accept 1080P50, and downscale it - but I've no idea now what percentage of current HD Ready sets will do that. I suspect their's probably quite a lot that still won't.

Bear in mind, the HD Ready specification doesn't require the set to accept 1080P at all, only 1080i and 720P.

Why would any mass market TV be designed to take a signal that isn't even broadcast yet? It just adds unnecessarily to the costs.

I think 1080p/50frames is allowed by EBU as a receiver enhancement but only higher end receivers are going to have it (as future-proofing). Most won't.

My last TV was certainly not the cheaper end of the market (My Son still has the same model). It was a 40" Sony Bravia at that time full HD TV's were virtually non existent and it cost well over a thousand pounds. I can't be certain it would not work with 1080p25 (sources are a bit rare) but it most definetely won't handle 1080p50 or 1080p60. When fed from a PS3 or a BD player it has to use pull down to get a 1080i 60 fps signal I believe. Setting an upscaling box to 1080p produces no picture either just an out of range message.

I would guess that 60fps

I would suspect that 60fps is a U.S.A. design - Years ago I had put timing adjustments into the video output of a micro so that scrolling did not make the viewer sick.