Producing good 24p - why the surprise? at DVinfo.net

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Sony HVR-Z1 / HDR-FX1
Pro and consumer versions of this Sony 3-CCD HDV camcorder.


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Old May 15th, 2005, 11:09 PM   #1
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Producing good 24p - why the surprise?

Maybe I'm dense or something but I read all the posts about progressive mode, Panasonic and JVC, and who is best. Doesn't Panasonic use interlace ccd's and do a pulldown in the camera software? The way I see it Sony captures more information in the 1080i in the FX1 and Z1 and then uses Vegas software to pull down and it is working with higher resolution images. What, if anything (and I don't see anything), makes pulldown in the camera superior to pulldown in the computer?

At NAB I saw beautiful 24p footage played out frame-by-frame with no artifacts. Each frame was clean and clear 24p footage. Now there is a post on the forum that FX1 footage can be put on 35mm film better than other DV cameras. This doesn't suprise me at all. I'll be the first person to admit I'm not a techie. So someone please explain it to me. Am I missing something?
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Old May 16th, 2005, 07:59 AM   #2
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You are right BUT

because every camera is very different (lense, ccd, ...) you need to compare them anyway. Raw mathematical comparisons may not be enough.


For easier calculations let's compare: 1080/50i with 1080/25p and 720/25p.

1) 1080/50i on the FX1/Z1 has an effective resolution of: 1440x540 every 50th of a second.

2) 1080/25p on real HDTV cams has an effective resolution of: 1920x1080 every 25th of a second.

3) 720/25p has a resolution of 1280x720 every 25th of a second.

a) Resolution comparison:

1) We have convert 50i to 25p. If you do it right (bottom of the page http://www.100fps.com/),
I would say with adaptive bob and weave and dropping every 2nd frame (2 interlaces frames
get interpolated into 2 progressive frames - 50p, dropping a frame does not mean anything bad)
you loose 5-15% of resolution. You can argue about that, because it's in certain areas and
of course adaptive. I do this just for resolution estimation and it should be between
average and worst case... for slow motion it's in my opinion max. 5% for fast motion it's worse.

Let's say we get: 1440x972 (1080-10%) = 1.4 M pixel every 25th of a second

2) That's simple: 1920x1080 = 2 M pixel every 25th of a second

3) Simple too: 0.9 M pixel every 25th of a second

It's clear that even if my calculations in 1) are not entirely right we still get a simple order:

1080/25p (HDTV 1080p) > 1080/50i (HDV: FX1/Z1) > 720/25p (HDTV 720p: JVC)

HDV is exactly in between.

b) Mathematical comparison:

As long as you don't convert 50i to 25p they are mathematically the same. You have the same amount
of information over the same time. 50i has more information on the time axis and 25p has more
information on the resolution axis. There is one further thing: 2 interlaced frames are connected
through odd/even lines. On conversion you have to use time information to interpolate resolution
information. Everything screams Fourier-transform or Wavelets right now. So a good de-interlacing
would be an adaptive bob/weave + correction in Fourier-space. So it is mathematically possible to
generate a very good (on average) 25p view of a 50i time flow especially because 2 frames are connected.

With HDV we have a second problem: 1440 rows only. So each row is 1.333333 pixels wide after being scaled up
to 1920. This up-scaling is the source of the major part of resolution drop to HDTV 1080 progressive.

c) Subjective comparison:

Neither resolution nor mathematical comparisons should be making up your decision. *You* are making the
decision, but facts and estimations can help - a lot. But don't forget to look at the results:

http://www.hd-channel.com/index.html?/programme.html
http://www.vasst.com/HDV/hdvportal.htm

One thing I can't recommend is to use the CF24 mode on NTSC cams and the CF25/30 modes in general:

CF24 does a pulldown (drops) + average of one frame (blend)
CF25/30 drop every second frame an up-scales the rest.

http://www.adamwilt.com/HDV/cineframe.html

CF25/30 *can* be ok if you target 720/25p, but forget them for 1080/25p you loose to much.

However I would always do the de-interlacing in software, the camera has no processing power for that.

I recommend looking at the results and then decide what you need.

Conclusion:

If we look at the resolution comparison again:

1080/25p (HDTV 1080p) > 1080/50i (HDV: FX1/Z1) > 720/25p (HDTV 720p: JVC)

and look at the price:

True HDTV: *very* expensive
JVC HD-100: 6000 EUR
Sony HVR-Z1: 5500 EUR
Sony HDR-FX1: 3000 EUR
HD-10: 2500 EUR

The FX1 is a real deal and *even* if you want to do 24p using the PAL model shooting 50i and de-interlacing
plus slowing down the movie by 4% is a good option.
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Old May 16th, 2005, 08:37 AM   #3
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The 100 fps link does not work. The HD Channel link seems to have some intersting info but it is in German. What is their verdict on the various FX1 modes?

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Old May 16th, 2005, 08:45 AM   #4
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1) http://www.100fps.com/

No ) at the end.

2) On HD-channel you can download short movies and compare them yourself. The camera model and the resolution should be no problem for english speaking people.

There is no verdict. Have a look yourself :)
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Old May 16th, 2005, 06:25 PM   #5
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Thanks, Armin. That is what I wanted. Valid info from a techie and, basically, my opinions are the same. I'm glad I bought the Z1.
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Old May 19th, 2005, 04:02 AM   #6
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If you ever need to translate a webpage. for example German as above or even Japanese if you need ;)
Here is the link that you can put directly in your favorites.

http://babelfish.altavista.com/
or
http://www.altavista.com then the link "translate"


Best regards
Bjorn

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Real men dont do backups they just cry
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