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Canon VIXIA Series AVCHD and HDV Camcorders
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Old July 25th, 2007, 06:57 PM   #1
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Confused about 24p

Note from Admin: I've changed the title of this thread from "HV20 does not record 24p" to the much more appropriate "Confused about 24p." --CH

I dont understand why I seem to be the only person on the planet to notice how the alledged 24p signal recorded by the HV20 can not be properly 'pulled up' from tape, no matter what process you use. I am a pro videographer of 27 years and pro visual FX artists of 12 years. Ive read countless forums about the topic and yes, I understand exactly how the post pullup is suppose to work. But the HV20 is most certainly falsely advertised as being 24progressive. First, the HV20 camcorder does not record 24p, it records only 30 frame interlaced with 2:3 pulldown. This is not progressive by any definition. But the bigger issue is that the 24p can not be properly pulled up from the tape, whether performed during or after capture.

Example- http://www.box.net/shared/static/nfs5rly5x7.jpg

Just as everyone else, I would gladly overlook the 2:3 pulldown recorded by the HV20, except that after executing the required 2:3 pullup, my wife (also a professional videographer and visual FX artist) and I immediately noticed 'strobey' playback. Looking closely, I see that every 4th frame has residual interlacing. ... how is this 'progressive?' A signal is either progressive or interlaced. The HV20 records interlaced, and the interlacing can not be entirely removed with a pullup in any software you care to name. It is bizarre to us that no one else seems to notice the problem.

Cineform CTO, David Newman explained the problem very clearly-

"CineForm Aspect HD does support automatic extraction of 24p from HV20's 60i stream. However, Ridlen is correct that the 60i encoding of 24p is not completely reversible, whereas the in 24F in the XH-A1 and XL-H1 is it. The reason the lack of completely reversibility is the 4:2:0 60i encoding which has only chroma value for pixels over two scan lines -- these scan lines may contain data from different frames, cause chroma cross-talk. The luminance is perfectly correct. Luma is encoded at 60i, and chroma at 30p, you can extract 24p from luma but not fully from chroma. If the pulldown is extracted correctly, the chroma cross-talk will only appear on every fourth frame. As our eyes are far more sensitive to luma, it is very hard to see this in motion. The only time this can be an issue is when keying, for that I recommend using HDMI and shooting live via the Black Magic Intensity card (using the new 1.5 drivers.)"

Why is no one else seeing this? I see no mention of it anywhere on this forum.

Heres a brief (10mb MPG2) example clip recorded in 24p with the HV20-
http://www.box.net/shared/static/grc3vdk59d.mpeg

Here are examples of every fourth frame after pullup in Digital Fusion.
http://www.box.net/shared/static/qg6v6mc7re.tga
http://www.box.net/shared/static/ym1bt6d2ud.tga

Fields remain in every 4th frame. This is NOT 'P' as in 'progressive.'

The only way I could completely get rid of the 4th frame interlacing after pullup was to run a 'strip and interpolate field 1,' then a 'strip and interpolate field 2' in Fusion. But then you quite noticeably lose vertical resolution from two passes of vertical interpolation.
http://www.box.net/shared/static/rgvfqtzu9r.jpg
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Old July 25th, 2007, 07:12 PM   #2
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I only recently got the camera, but I don't doubt this issue at all ... though in the tiny amount of footage I've shot (plus that of others that I've reviewed) this anomaly doesn't appear to be glaring enough to be that noticably on typical footage.

I'm not sure that this invalidates the fact that it does capture a progressive image and encode it into a 60i stream on tape. It may not do it exactly correctly, and I wish it did, but in perspective it doesn't seem like a huge issue for a $1k camera.
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Old July 25th, 2007, 07:19 PM   #3
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I stupidly shot, before fully testing all aspects of the camera, ten hours of footage in 24p for a doc and . . . . I couldn't be more upset about the state of affairs. I've emailed canon and they've been polite but basically they just keep telling me to buy the A1 if I want true 24p. I was planning on buying cineform but, in layman's terms, are you saying that even with cineform the HV20's 24p is not really 24p and the footage will be sub par?
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Old July 25th, 2007, 07:25 PM   #4
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if you bypass the tape recording and record straight to hard drive you'd get 24p though
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Old July 25th, 2007, 08:01 PM   #5
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The HV20's 24p mode is awesome. Unfortunately, due to user errors, not everyone's footage turns out correctly from this camera.

Don't bash a camera that's already been tested and proven to work as advertised. Maybe consider yourself as the culprit and ask for assistance in how to process the footage correctly. You also may want to consider removing your "review" on CNet, as it too is completely inaccurate.

-Pasty
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Old July 25th, 2007, 08:04 PM   #6
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>if you bypass the tape recording and record straight to hard drive you'd get 24p though

Is this true? Do you need extra hardware or through plain firewire this would work? Which apps can record and in which format?

Regarding 24f, it is known that the HV20 is not 24p when it writes on tape. However, using several methods of removing pulldown, I got a very good result. Apparently Premiere LE does NOT do it the right way btw resulting in these artifacts David is showing in his pic.
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Old July 25th, 2007, 09:47 PM   #7
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I am not sure what the issues are technically, but I've been shooting HV20 in 24p, capturing with NeoHDV from Cineform. In Vegas, I have sent the footage to HD 24p and if it ain't real, it still looks pretty good....
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Old July 25th, 2007, 11:21 PM   #8
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While everything David Ridlen is saying is true, I don't see much cause for alarm. We at a CineForm recently extracted 24p from tape based captures using a HV20 and displayed to results via a Sony 4K projector at a local Landmark Theater -- looked pretty good. Yes direct capture from the HDMI (not Firewire) is better, both for pulldown to 24p, avoiding MPEG compression artifacts, and the evil 4:2:0 subsampling. You see the last two issues well before you see the 24p chroma crosstalk. Live capture from HDMI port is "perfect", for that you need a Blackmagic Intensity card and preferrably CineForm's NEO HDV or HD. Note: The Sony V1U has the same minor 24p issues if you record to tape. As for using Canon A1 24F instead of the HV20 in 24p, yes the A1 is a better camera, however I find the progressive look of the HV20 is more natural -- the Canon 24F mode lacks vertical resolution and introduces aliasing.
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Old July 26th, 2007, 02:30 AM   #9
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Quote:
Originally Posted by David Newman View Post
While everything David Ridlen is saying is true, I don't see much cause for alarm. We at a CineForm recently extracted 24p from tape based captures using a HV20 and displayed to results via a Sony 4K projector at a local Landmark Theater -- looked pretty good. Yes direct capture from the HDMI (not Firewire) is better, both for pulldown to 24p, avoiding MPEG compression artifacts, and the evil 4:2:0 subsampling. You see the last two issues well before you see the 24p chroma crosstalk. Live capture from HDMI port is "perfect", for that you need a Blackmagic Intensity card and preferrably CineForm's NEO HDV or HD. Note: The Sony V1U has the same minor 24p issues if you record to tape. As for using Canon A1 24F instead of the HV20 in 24p, yes the A1 is a better camera, however I find the progressive look of the HV20 is more natural -- the Canon 24F mode lacks vertical resolution and introduces aliasing.
David, I'm sorry for asking such a basic question, but my head is spinning from trying to keep so many plates up in the air.

Does Cineform NEO HD deinterlace 60i (I'll probably be using a combination of a Sony FX-1 and a Canon HV-20) to 24 progressive frames per second? And if so, how does it handle motion and how much vertical resolution is lost?

I understand that Apple's Compressor 3 is quite good at this, but I'm in the pc world, and of course would rather give CineForm the business.

Thanks MUCH!
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Old July 26th, 2007, 05:01 AM   #10
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Quote:
Originally Posted by David Newman View Post
While everything David Ridlen is saying is true, I don't see much cause for alarm.
I shot quick tests of a black glove waving in front of white, red, green and blue backgrounds. As expected, the chroma/field bleed is most apparent in the red channel, green next, a little less in the blues, while the white background shows no interlacing problem since the luma values are not affected. And if you post process the HV20's neutral 'cinemode' footage by pushing saturation or black levels, as anyone might quite naturally do, the problem quickly looks much worse. I really dont know how anyone can think that this is okay to have playing back on every fourth frame.
red
http://www.box.net/shared/static/zmvek4rvan.jpg
green
http://www.box.net/shared/static/2vqcguo1oc.jpg
blue
http://www.box.net/shared/static/uhdlh6rtky.jpg


Quote:
Originally Posted by David Newman View Post
...Live capture from HDMI port is "perfect",
Yes, but again I ask, who expects a 24p camcorder to neither record nor playback 24p? How many HV20 owners fully anticipated always having to shoot while hooked to a computer in a studio situation to obtain clean 24p? I sure did not. I also anticipated being able to key elements I shot with the HV20, which is an even a bigger mess with the fourth frame interlacing.

Wikipedia defines a camcorder as "... a portable electronic device for recording video images and audio onto an internal storage device." Therefore, a '24p camcorder' should record '24p' on an 'internal storage device.' The Hv20 does not record 24p, so it is not a 24p camcorder. And the 24p can not be properly converted from the tape due to this fourth frame residual interlacing problem.

I dont see how anyone can find the 24p aspect of the HV20 anything but dissapointing. I also fail to see how Canon's '24p' claim of the HV20 camcorder is not at the very least, misleading advertising.
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Old July 26th, 2007, 05:57 AM   #11
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It's a $1k camcorder for soccer mums....
GET OVER IT

Be grateful Canon is testing their new 24p-capable CMOS chips on a consumer cam. They know full-well a lot of pros and indie people are using the HV20 and pushing it to its limits - the feedback they give to Canon will hopefully go into their next generation 3-CMOS pro camcorder without the headaches if they had released a "pro" HV20 simulatenously with the HV20.

Once again.... the HV20 is a TOY...... a very nifty, very cool toy, but a toy all the same.
GET OVER IT
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Old July 26th, 2007, 05:59 AM   #12
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Life is so much easier with PAL and 25p could you consider importing a PAL unit?
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Old July 26th, 2007, 06:14 AM   #13
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I suspect the problem being described is nothing to do with capture but is due to the way the image data is being compressed.
Image compression algorithms are typically designed to exploit pixel-to-pixel coherence in the image. Consequently smooth images compress better than un-smooth ones.

The way the (NTSC) HV20 is laying down frames means that every other frame is a "mouse toothed" interleaved frame. These frames will be a tougher to compress and compression errors will cause some crosstalk between fields.

On the other hand, the PAL version doesn't need to do this.

Why doesn't the Camcorder industry just drop this regional / historical nonsense?
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Old July 26th, 2007, 06:14 AM   #14
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The 24P mode looks pretty good to me. I have no complaints on that issue...

It sounds more like, can Mr Ridlen come up with a better solution for $1000 ??

Please let us know...

Thanks
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Old July 26th, 2007, 08:05 AM   #15
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There's a thread over on DVXUSer about this that pretty much contradicts everything in the orginal post. Barry Green, in particular says that it is true 24p.
http://www.dvxuser.com/V6/showthread.php?t=104714
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