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Canon XL and GL Series DV Camcorders
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Old July 20th, 2004, 10:59 AM   #1
 
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Confused about pulldown

I'm standing here my ingnorance for all to see, but I have a question. Some of these concepts are still, after four years, hard for me to grasp.

For example, on the Canon site regarding the new frame rate, it states:"24p, 2:3. . . The 2:3 pulldown is the conversion method to convert 24p to 60i so that video shot in either 24p frame rates can be viewed on a television."

If something is shot in 24p then converted to 60i (standard video), isn't the "look" of 24p lost in that conversion process?

Thanks for your patience and hopefully the lack of ridicule. ;o)

Jay
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Old July 20th, 2004, 11:38 AM   #2
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I could be wrong here but I think 2:3 is the doubling method, so in order to get 24P to look like 30p (and then 60i) the first fram stays the same and then the second one appears twice, the third and fourth frame appear the same and then the fifth is doubled. so the look of film won't be lost, as there will be 24 different frames and then 6 doubled frames, the different types of pull down (2:3 or 2:3:3:2) decide which get doubled.
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Old July 20th, 2004, 12:08 PM   #3
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I'm going to say this another way...using the 2:3 pull down on the xl2 will make your footage look like a standard 24 fps film that has been converted for television. So it looks like film does on TV.

the 2:3:3:2 method is used for eventual output to film.

Barry
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Old July 20th, 2004, 12:50 PM   #4
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I guess I'm lucky living in Pal land, when I (if I can afford to) get a Pal XL2, it will have 25p, so no need for a pulldown method, and editing is a breeze. 25p can also go to film frame by frame.

Its a shame the US isn't Pal based, because it has three main advantages that I can see over NTSC: 25p, 720x576 and 4:2:1 sampling (right?).

I once read that NTSC stands for 'Never The Same Color', I suppose it could have been a joke ;)

Dave.
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Old July 20th, 2004, 01:09 PM   #5
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Dave, PAL sampling is 4:2:0, but still generally perceived to be better than NYSC's 4:1:1
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Old July 20th, 2004, 04:14 PM   #6
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To Dave, I think it isn't a joke, NTSC really stands for Never The Same Color.
I'm not completely sure, but I think it is...
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Old July 20th, 2004, 04:40 PM   #7
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Quote:
Originally posted by Mathieu Ghekiere
To Dave, I think it isn't a joke, NTSC really stands for Never The Same Color.
I'm not completely sure, but I think it is...
Looks like it might be something along those lines: see AcronymFinder.com.
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Old July 21st, 2004, 12:15 AM   #8
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National Television Standards Committee or National Television System Committee.
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Old July 21st, 2004, 01:14 AM   #9
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Somehow Never Twice the Same Colour suits it better....

Err...
I mean
Barry is correct....
Of course in other parts of the world there is the Perfection At Last system. Or is it the Pay A Lot system...?
Does anyone have any good acronyms for SECAM?
Does anyone ever care about SECAM? :)

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Old July 21st, 2004, 05:12 AM   #10
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I'm in PAL land. Not sure about quality diferences between PAL and NTSC, but sure thing: PAL = "Pay A Lot system" :)
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Old July 22nd, 2004, 01:31 PM   #11
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The "Never Twice the Same Colour" was an expression that emanated from BBC Television vision engineers in London who were dismayed at the quality of VT recordings coming over to Europe from the US in the 60s (before the UK and other European countries like Germany had yet agreed and implemented a common standard that was to be PAL 625).

Originally, transmission masters came as 2" Quad or 2" Helical reels in NTSC, and BBC Engineering in Wood Norton developed a "black box" that enabled a signal of one standard to be fed in one end and a converted signal of another standard to come out of the other. This was the first Standards Converter. Trouble is, shows like Dallas started to come over having been converted from NTSC to PAL and the quality was abysmal. Much argument and negotiation ensued.

At its root, the problem stemmed from the fact that NTSC TV sets had (still have??) a "Hue" control which if used casually can wreak havoc on pictures. PAL receivers have never had this, hence the relative stability and consistency of the pictures by comparison.

Colin
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Old July 22nd, 2004, 06:00 PM   #12
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Yep, we still have "hue", although sometimes it's called "color phase"...
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Old July 22nd, 2004, 06:23 PM   #13
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<<<-- Originally posted by Colin Barrett : Much argument and negotiation ensued. Colin -->>>

That sentence about the NTSC vs. PAL debate could probably be the basis for a very good movie. Maybe two, one dramatic and one comical.

Oh to be a fly on the wall when that "argument and negotiation ensued"!
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Old August 2nd, 2004, 09:39 AM   #14
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To answer the original question you should not loose the 24p
effect or any quality etc. The effect that is being done is totally
reversible if the software does it correctly.

Let's give an over simplified explenation:

We have 4 frames: 1, 2, 3 & 4 which are 8 fields (11, 22, 33, 44)

Now put these in 2:3 mode together and you get:

11 222 33 444

Now each frame has two fields so you get:

11 22 23 34 44

24 frames + 6 frames (24 / 2 / 2) = 30 fps

To decode this you do the reverse:

11 22 23 34 44

expand this to

11 222 33 444

now remove the duplicate 2 & 4 fields (they are just duplicates)
and you get: 11 22 33 44

These are your new frames and you are back at 24 fps.

2:3:3:2 is similar, your sequence would be:

11 222 333 44 instead of 11 222 33 444

I hope this explains it a bit better. It is just a way to store 24 fps
in 30 fps without throwing away information.

This makes it playable at 30 fps and with the correct software you
can transform it back to 24 fps.

The same process is used for transferring a film to a video tape.
DVD stores just the 24 frames per second. Basically your editing
program (like vegas) transforms it back again.

Also see the diagrams on this page to see it in a more
graphical form.
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