Inverse telecine question

[blwegrzyn]

I have pc connected to my hdtv through dvi to hdmi 720P.
Nvidia cards have an option to enable inverse telecine which is supposed to convert content from 29.97fps to 24fps.
Now if my screen is set to refresh rate of 60HZ and the video is converted to 24fps would I really benefit from it?
If the screen refreshes 60 times in one sec and the video plays 24 frames per sec how this would be displayed?
Will it have to be converted again?

thx

[stanger89]

Yes you would. IVTC doesn't "convert" 30fps to 24fps, it recovers the original 24fps progressive film content from the 60Hz interlaced container it's placed in when encoded. This means you don't lose the detail that's there like you can when you deinterlace telecined film. You won't however get the benefit of displaying film at an even multiple of it's frame rate.

[blwegrzyn]

So, Why Nvidia describes it as:
"provides more accurate movie playback and superior picture quality by recovering original images from films converted to video (eg DVD, 1080I)"

Whats the catch here?

[stanger89]

What do you mean?

[blwegrzyn]

So the original movie is recorded in 24fps.
Then the telecine is applied and the movie is 29.97 fps
The movie is played on the computer dvd player that is connected to lets say 1080I. Without inverse telecine 29.97 frames are sent to tv?
If the inverse telecine is applied original 24 frames are restored and what is sent to the tv??? Does the tv should be in progressive mode for this to make any sense? If the refresh rate is 60Hz 24 would have to be again converted to 29.97, right? So as you said there would no point of enabling it? Is above process correct?

But nvidia advertises that it is supposed to help and make the picture look better?

Also I have another question? In case of cinema movies when they are recorded at 24fps at which point the interlacing is applied? Almost all dvds are in interlaced mode.


thx

[blwegrzyn]

Guys here are my findings,

first the video is recorded at 24fps progressive,
then 3:2 pulldown is applied and it already includes interlacing,
so the final signal is at 59.94 interlaced,

The inverse telecine would recover original 24fps, but because almost all tvs refreshes at 60Hz there is no point in doing this? For this to work the tv must be able to accept 24fps or it must be refreshing at multiples of 24 (72HZ) Currently no one makes such tvs. So the inverse telecine is useless !!!

so in case of progressive screens , the only thing that happens is the process of deinteralcing the signal so it can be transmitted using progressive mode,

The good deinteralcer is very important part of good quality picture !!!
I use cyberlink codec with hardware nvidia de interlacing and in my case the BOB method works the best. Nvidia calls it Display Fields Separately.

thx

[stanger89]

Originally Posted by blwegrzyn

Guys here are my findings,

first the video is recorded at 24fps progressive,
then 3:2 pulldown is applied and it already includes interlacing,
so the final signal is at 59.94 interlaced,

The inverse telecine would recover original 24fps, but because almost all tvs refreshes at 60Hz there is no point in doing this?

No, there is a point because you're feeding progressive video to the TV, not interelace, so that means one out of every five frames (from the 59.94 interlaced fields) contains fields from two different frames of the movie. This results in at worst combing, and at best loss of detail because that odd frame needs to be deinterlaced.

IVCT avoid deinterlacing entirely, putting the original progressive frames back together.

For this to work the tv must be able to accept 24fps or it must be refreshing at multiples of 24 (72HZ) Currently no one makes such tvs. So the inverse telecine is useless !!!

No, this is another issue.

so in case of progressive screens , the only thing that happens is the process of deinteralcing the signal so it can be transmitted using progressive mode,

You lost me there. DVD is stored as 480i60, but it's 24fps film telecined into that storage medium. IVTC recovers that original 24 fps progressive content so that further video processing (scaling, frame rate conversion) can be done cleanly.

The good deinteralcer is very important part of good quality picture !!!

Yes it is, but it's best to avoid deinterlacing entirely. That's what IVTC is for, to recover the original progressive frames so deinterlacing isn't necessary.

I use cyberlink codec with hardware nvidia de interlacing and in my case the BOB method works the best. Nvidia calls it Display Fields Separately.

BOB is combine field, Weave is display fields separately.

[blwegrzyn]

Originally Posted by stanger89

Yes it is, but it's best to avoid deinterlacing entirely. That's what IVTC is for, to recover the original progressive frames so deinterlacing isn't necessary.

I understand, but if I recover frames i will end up with 24fps progressive.
How will I send it to the tv if my card is sending 60HZ progressive?
My understanding is that 24fps cannot be accept by tv, so I dont see any benefit.

Originally Posted by stanger89

BOB is combine field, Weave is display fields separately.

sorry for the mistake

[blwegrzyn]

Originally Posted by stanger89

You lost me there. DVD is stored as 480i60, but it's 24fps film telecined into that storage medium. IVTC recovers that original 24 fps progressive content so that further video processing (scaling, frame rate conversion) can be done cleanly.

As far as I know in the telecin process 24fps are converted to 29.96 and interlaced.

Original frame: A B C D <<<<< progresive

Telecined:

A B B C D <<<<< you see the interlacing here
A B C C D

Inverse telecine will restore original , but the tv must be able to receive 24fps,
If it cannot the Inverse Telecined signal must be deinterlaced using one of the available deinterlacing methods ,

[stanger89]

The problem is that first C you've got up there is a mix of the top field from B and the bottom field from C. Take a look at this:
http://www.hometheaterhifi.com/volum...e-10-2000.html

[evilpenguin]

Here's another good write up from the devs over at Handbrake...

http://trac.handbrake.fr/wiki/Telecine

[blwegrzyn]

hmm, I am not sure if I am right , but in your link it is done in reverse order:
according to
http://en.wikipedia.org/wiki/Telecine

"In the United States and other countries with television using 60Hz vertical scanning frequency, video is broadcast at 29.97 frame/s. For the film's motion to be accurately rendered on the video signal, a telecine must use a technique called the 2:3 pulldown (sometimes also called 3:2 pulldown) to convert from 24 to 29.97 frame/s."

It is called sometimes 3:2 because this is what actually happens during the conversion. See attached screens to compare and please correct me if I am wrong.

[sandor]

all of this is why display manufacturers are pushing 120 hz, right? compatible with 24, 30 and 60 FPS content..

[babgvant]

Originally Posted by sandor

all of this is why display manufacturers are pushing 120 hz, right? compatible with 24, 30 and 60 FPS content..

120Hz is for motion blur on LCD panels, but it does make 5:5 pulldown instead of a 2:3 (3:2) possible.

[blwegrzyn]

here is how I ended up:
Because my tv has native resolution of 1080i, i use my pc to send 1080i.
I could use 720P but I decided to use native resolution.
Because most of the dvd material is interlaced, i dont have to do any deinteralcing and I must admint that the interlaced signal looks preety good.
Also, because my tv cannot accept 24fps i dont have to worry about inverse telecine. The only question I have is:
When the blue ray is 30p progressive and the inversetelecine is applied, the original 24 frames are restored, and then what? The tv is 60HZ so what actually happens with the signal sent to the tv?
Does the card have to convert it again, if yes what conversion?

thx

[stanger89]

Originally Posted by blwegrzyn

here is how I ended up:
Because my tv has native resolution of 1080i, i use my pc to send 1080i.
I could use 720P but I decided to use native resolution.
Because most of the dvd material is interlaced, i dont have to do any deinteralcing and I must admint that the interlaced signal looks preety good.

Yes you do have to deinterlace, interlace video can't be scaled without introducing horrible artifacts:

Also, because my tv cannot accept 24fps i dont have to worry about inverse telecine. The only question I have is:

But you do, or you should. You have to "convert" the interlaced 480i on DVD to progressive video in order to scale it to your desired output resolution. You can either Deinterlace (Bob, Weave, Motion-adaptive) or perform IVTC. Since film is progressive, IVTC is the best way, the only way to losslessly recover the original progressive frames.

Regardless of what resolution or framerate you want to be outputting finally, you need the original progressive frames for optimal processing that's required.

When the blue ray is 30p progressive and the inversetelecine is applied, the original 24 frames are restored, and then what? The tv is 60HZ so what actually happens with the signal sent to the tv?
Does the card have to convert it again, if yes what conversion?

Regardless of the source, once you have those original frames back, the video card will duplicate frames (usually the 3:2 cadence) to pad the output back up to your output framerate (ie 60Hz).

[blwegrzyn]

Originally Posted by stanger89

Regardless of the source, once you have those original frames back, the video card will duplicate frames (usually the 3:2 cadence) to pad the output back up to your output framerate (ie 60Hz).

Does not above sound like doing everything again back to interlaced and then progressive? You get 24 frames back then you do 3:2 so you interlace and the you must deinterlace to sent it to 60HZ?

[blwegrzyn]

stanger89, I am really confused about all that staff we talked about,
I understand your points but it is hard for me to understand and believe, I still feel not convinced, sorry

so you say:
interlaced signal must be deinterlaced so it can be output interlaced becasue it must be converted? So:

original 24fps > 3:2 > 59.96 interlaced > is this what is recorded to DVD?

on pc:
DVD > IVTC > 24fps > interlaced signal (would not this be exacly what was on DVD) > deinterlace > output to tv ???

I performed some tests with playing the original interlaced signal on my pc and the only way to get the correct output was to disable deinterlacing and IVTC.
The input signal was from here:
http://www.kingcot.eclipse.co.uk/uni...tvoutTest.html

and it was output as 1080 and it contained everything as in original signal.
Once the deinterlacing and IVTC were enabled signal was not perfect (Blinking and problems with the line)

What do you think?

[Patilan]

Guys, do yourself a favor and do what stanger89 said.

If you are able to recover the original 24 progressive frames, your job is done!

Keep it at 24, and don't worry where you'll be feeding it for playback. Any modern output device is most happy when you give it exactly that.

Besides, a good quality transcoding can be done only if you have that original 24 progressive video. Any scaling, transcoding, etc. on interlaced and/or telecined source produces garbage.

[blwegrzyn]

I have read this:
http://www.mplayerhq.hu/DOCS/HTML/en...-telecine.html

and Thank you for your helpful lessons.

I came to the conclusion:
As you said anytime the video is going to be scaled, it is good to use ITVC.
So, ITVC would not be necessary if the video would be send as it is directly to tv which would match the input format.