[Rebies]

Okay, I understand what 3:2 pulldown is and how it works, but I have some simple questions I was not able to find the answers to when searching the forums...


1) What happens if there is no 3:2 pulldown? Will a one minute film clip play back in 48 seconds? Is the image quality just not going to be as sharp? I simply don't understand this as a one hour movie being shortened to 48 minutes would be unbearable to watch, right? Thus I would assume that 3:2 pulldown would be needed in every single DVD player making it a trivial thing for the actual TVs to implement.


2) How does 3:2 effect a HDTV as opposed to regular NTSC television? Or is there no difference in how 3:2 is needed on both TV types? I see it as DVD is DVD, and it needs 3:2 pulldown to show film at 30 fps.


3) What are considered "film based" mediums that are effected by the 24 fps to 30 fps (60 fields)? DVD and LD, right? What about VHS, Cable and Sat: Are these not effected in any way?


Thanks for any help. I hope these questions are not as simple as they seem because I spent a bit of time searching on the topic before actually posting.

 

[Glimmie]

Quote:

Originally posted by Rebies Okay, I understand what 3:2 pulldown is and how it works, but I have some simple questions I was not able to find the answers to when searching the forums... 1) What happens if there is no 3:2 pulldown? Will a one minute film clip play back in 48 seconds? Is the image quality just not going to be as sharp? I simply don't understand this as a one hour movie being shortened to 48 minutes would be unbearable to watch, right? Thus I would assume that 3:2 pulldown would be needed in every single DVD player making it a trivial thing for the actual TVs to implement.

In a transfer to video, you have to make 24 pictures fit into 30. There is no way to do this other than 3/2 pull down. Some commericals are shot on 30 frame film to reduce atrifactes of 3/2. In this case the film is simply tansfered frame to frame. New mastering techniques however are being used in some facilities that do transfer film at 24 frames to video. This makes a master which is simply played back with 3/2 pulldown added to make either NTSC or HDTV versions. For PAL we simply run the master tape 4% faster to make 25 frames. This is exactly how a PAL transfer is done, they run the film 4% faster. The main reason TV shows are not shot at 30 frames is film cost. Shows are sometimes shot as much as 8to1 ratio of footage versus running time. That's a lot of wasted film, even more at 30frames. To save even more money some shows use 3pref framing. This shortens the blank bar between the film frames and uses less footage for the same running time.


Don't confuse running time with sampling time. A film camera samples the image 24 times a second. A television camera or film scanner samples the image 30 frames a second (really 60 every other line for interlaced formats). It's just a matter of which pictures you duplicate to equal the same running time. Even with 3/2 you are still only seeing 24 unique pictures per second because that's all there is recorded on the film.


3/2 pull down is no longer a film issue either. More and more shows are being shot in 24 frame HDTV video. Here 3/2 pulldown is added somewhere along the process to make 30 frames.

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2) How does 3:2 effect a HDTV as opposed to regular NTSC television? Or is there no difference in how 3:2 is needed on both TV types? I see it as DVD is DVD, and it needs 3:2 pulldown to show film at 30 fps.

There is no difference between NTSC and HDTV at 30 frames per second. The frame rate is the same and therefore 3/2 pulldown is the same. The only difference is more lines and pixels in a HDTV image.

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3) What are considered "film based" mediums that are effected by the 24 fps to 30 fps (60 fields)? DVD and LD, right? What about VHS, Cable and Sat: Are these not effected in any way?

3/2 pulldown is added to ANY 24frame native material, film or video. It makes no difference what the end distribution medium is.

A VHS movie has 3/2 pulldown added. So does a movie over satellite. I should note that even your local theatre does not show 24 frames per second. They double flash each frame to make 48 pictures per second. 24 frames would flicker severely. Even 48 is too slow but since a theatre is about 16fl illumination, you don't really notice it. I a typical TV environment 48 frames would flicker because the average illumination on the screen is abot 25fl. If you ever saw PAL video at 50frames, it does flicker until you get used to it. Ask a European how they can stand that flickering picture and they will respond "What flicker". You do get used to it.

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Thanks for any help. I hope these questions are not as simple as they seem because I spent a bit of time searching on the topic before actually posting.

 

[Rebies]

Quote:

3/2 pull down is no longer a film issue either. More and more shows are being shot in 24 frame HDTV video. Here 3/2 pulldown is added somewhere along the process to make 30 frames.

What if your TV does not have a 3/2 pulldown feature? What if your STB and TV don't have this. Will the video look very bad? Will it be a lot faster?


I'm trying to figure out how important it is having 3/2 pulldown on the TV itself and or the STB. Also trying to figure out if its best leaving the 3/2 conversion to the TV or the STB.

 

[Glimmie]

Quote:

Originally posted by Rebies What if your TV does not have a 3/2 pulldown feature? What if your STB and TV don't have this. Will the video look very bad? Will it be a lot faster? I'm trying to figure out how important it is having 3/2 pulldown on the TV itself and or the STB. Also trying to figure out if its best leaving the 3/2 conversion to the TV or the STB.

You will always have 3/2 added in some form. The 3/2 may be added in your DBS receiver if the image is being transmitted in 24frame to save bit space. If it's OTA, it's there to begin with. The TV or display device expects to have it in the signal. It doesn't add it.


This is not a concern when shopping for video equipment if you are simply wanting to view the image. This issue on the consumer side comes into play when converting an interlaced image to a progressing image. What they are advertising is 3/2 REMOVAL, not insertion. To spite many claims 3/2 can never be flawlessly reversed on consumer equipment. That's because you have no idea of the cadance start. The way it's done without a reference is to study several fields of video and look for the duplicated ones, then disgard them to restore the origional 24 frame pictures. Sounds simple enough but there is a problem. Any film scanner is analog and adds noise. Digital transmission paths, especially DBS are not error free. All it takes is a missing pixel or a difference in the noise pattern between the video fields and the 3/2 removal circuits get confused. Now you can weigh the outcome and do further processing but that's beyond consumer price scales. And it's still never 100% reliable no matter how much hardware and software you throw at it.


In the broadcast enviornment we have a frame count signal married to the video signal. It's called timecode and is either an analog signal - LTC or embedded in the video signal- VITC. From this we can reference the 3/2 cadance start from these numbers PROVIDED THE TIMECODE WAS NOT ALTERED and it often is. See, even with the right tools it's not 100% perfect.

 

[wirehead_rick]

I think pictures speak better than words. Therefore I strongly urge you to read this artice:

http://www.hometheaterhifi.com/volum...e-10-2000.html


It has the best explaination and graphics to convey all the information you need to understand 3:2 pulldown.


One more thing. If you really don't want to read the entire article at least begin reading at the section titled: "An Explanation of Film-to-Video Frame Rate Conversion for NTSC".


Enjoy!


Rick

 

[trbarry]

Quote:

To spite many claims 3/2 can never be flawlessly reversed on consumer equipment. That's because you have no idea of the cadance start. The way it's done without a reference is to study several fields of video and look for the duplicated ones, then disgard them to restore the origional 24 frame pictures. Sounds simple enough but there is a problem. Any film scanner is analog and adds noise.

From the point of view of consumer electronics or DScaler software it is actually not hard to do pulldown removal, though I omit the word flawless. All you have to do is match up the fields and then delete the frames most likely to be duplicates. This usually works even in presence of noise and cadence changes.


The big problem is deciding whether you SHOULD be doing this. It is very hard to know accurately and rapidly if a show has changed from telecined material to interlaced material from a video source. And that transition happens often in the real world.


- Tom