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Old January 4th, 2007, 10:45 AM   #1
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24P - Camera is still, Motion is Juddery

Hello Everyone! This is my first post on dvinfo but I've been reading this forum for a long time. I have owned my HD100 for about a 8 months and use it for weddings and coporate videos. I've had great results with everything I've done in 30P HDV.

Now, for my question:

As a complete novice in 24P shooting, and I do mean complete, I understand why holding my camera (handheld) and moving it around quickly makes the images look juddery. But, my question relates to if I have the camera on a tripod and am shooting something moving in the frame, it looks just as juddery. For example, I tested it last night with my pool table. The image quality is amazing and brings out the colors in the balls brilliantly, but when they move it looks bad. I've seen countless movies where pool balls and other objects are moving really fast but don't seem to look like what I shot.

Is there a correction to this? (Motion smoothing gives me the unwanted extreme blur effect)
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Old January 4th, 2007, 11:16 AM   #2
 
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imho, that's just the nature of progressive frame, m2t compression, the way jvc has chosen to do it. i think that's one reason jvc went to the 60fps capability on the 200/250 models. at 24fps, the interframe motion really plays games with the motion compression algorithms. it's not as bad at 30fps, but, i understand there's still some artifacts visible at 60fps on the new models. i don't much care for jvc's motion smoothing. things work fairly well as long as you're not panning. motion within the frame is handled OK. the problems arise when the entire frame is panned.

the camera sensor sees at a fixed rate of 60 frames per second. It then combines each frame in a way to yield 30, 25 or 24 fps. In effect you still are capturing 60 FIELDS per second, even if the fields are complete frames. When two frames that differ spacially are combined, panned frames are NOT identical and you get that ghosting that looks like crap on a panned image. JVC's motion smoothing is similar to the old way of combining interlaced footage to make it progressive. adjusting shutter speed does no good because the two combined frames still vary in spacial information. the REAL solution is to provide a stream of temporally and spacially unique frames that are NOT combined into a single frame.In a way, the ability to select frame rate is a little misleading because it doesn't change the fundamental way the sensor is viewing the scene...that is at 60 fps. The frame rate written to tape is the result of camera processing, not a native change to the way the sensor sees the scene.

Last edited by Bill Ravens; January 4th, 2007 at 11:55 AM.
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Old January 4th, 2007, 11:19 AM   #3
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Couldn't this particular situation be solved by adjusting your shudder speed?

I know all about the "ugly jitter" that can happen. It looks un-natural and very "un-film like."
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Old January 4th, 2007, 01:36 PM   #4
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Thank you for the detailed explanation - most of what you said was news to me. Again, when shooting 30P, everything looks fine, and now I understand a bit more as to why that is when compared to 24P.

To comment on the last post, isn't changing the shutter speed from anything other than 1/48 (or 1/24) not a good idea? I just want to expand my knowledge and skill in the 24P arena and don't want to start off by possibly doing band-aid fixes, if that even is one.

Ultimately, the 24P question is best answered as "That's just how it is with the HD100..." -- is that correct? I swear I've seen other videos from the HD100 at 24P from this forum that have motion and look great. I've never been able to come close to replicating smoother motion I've seen with other 24P projects.

I know that I am asking a lot in these questions, but I've never found a good answer and don't see why "if they can do it with the HD100, I should be able to also". I want to get into making short movies @ 24P and leave the 30P shooting for weddings/corporate projects.

This thread was just posted and the 24P footage looks amazing, nothing like my camera spits out, and I mean in terms of motion ONLY: http://www.dvinfo.net/conf/showthread.php?t=81871


Thank you again everyone for your help.
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Old January 5th, 2007, 12:57 AM   #5
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Bill's post is pretty much completely wrong. In 24p the camera scans the chip 48 times a second and writes every other scan to tape. Unless motion smoothing is on the frames you get in 24p are not interpolated in anyway.

The first thing you should probably sheck is whether your shutter is set to 1/48. A shutter speed of twice the frame rate gives you just enouhg motion blur to help your eye "connect" the images together to provide the illusion of smooth motion... As long as the motion in the frame isn't too extreme.
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Old January 5th, 2007, 01:02 AM   #6
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Quote:
Originally Posted by Stephan Ahonen
The first thing you should probably sheck is whether your shutter is set to 1/48. A shutter speed of twice the frame rate gives you just enouhg motion blur to help your eye "connect" the images together to provide the illusion of smooth motion... As long as the motion in the frame isn't too extreme.
Yes, check the shutter speed. I believe the camera defaults to 1/24 sec in 24p, and this is not correct... it should be 1/48. This is discussed in other threads.
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Old January 5th, 2007, 05:53 AM   #7
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Quote:
Originally Posted by Jack Walker
Yes, check the shutter speed. I believe the camera defaults to 1/24 sec in 24p, and this is not correct... it should be 1/48. This is discussed in other threads.
I believe that only occurs in SD.

TO JUSTIN - I have a pool table in my basement. Later tonight, I will set up the cam on a tripod and do a test for you myself annd see if the same thing happens.

I have really only been using 24P and have been alright. You have to remember, this is not a problem with the JVC, EVERY 24P cam does this. It is one of the issue with 24P. If you move the camera incorrectly, you get motion blur. In 24 Frames, there are very specific rules to follow in order to get everything correct.
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Old January 5th, 2007, 08:02 AM   #8
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Quote:
Originally Posted by Bill Ravens
imho, that's just the nature of progressive frame, m2t compression, the way jvc has chosen to do it. i think that's one reason jvc went to the 60fps capability on the 200/250 models. at 24fps, the interframe motion really plays games with the motion compression algorithms. it's not as bad at 30fps, but, i understand there's still some artifacts visible at 60fps on the new models. i don't much care for jvc's motion smoothing. things work fairly well as long as you're not panning. motion within the frame is handled OK. the problems arise when the entire frame is panned.

the camera sensor sees at a fixed rate of 60 frames per second. It then combines each frame in a way to yield 30, 25 or 24 fps. In effect you still are capturing 60 FIELDS per second, even if the fields are complete frames. When two frames that differ spacially are combined, panned frames are NOT identical and you get that ghosting that looks like crap on a panned image. JVC's motion smoothing is similar to the old way of combining interlaced footage to make it progressive. adjusting shutter speed does no good because the two combined frames still vary in spacial information. the REAL solution is to provide a stream of temporally and spacially unique frames that are NOT combined into a single frame.In a way, the ability to select frame rate is a little misleading because it doesn't change the fundamental way the sensor is viewing the scene...that is at 60 fps. The frame rate written to tape is the result of camera processing, not a native change to the way the sensor sees the scene.
Hi Bill,

Some of what you have here is right, but most of this doesn't apply to the HD100. Your explanations would apply better to a 1080i camera that shoots "24PsF" like the XLH1 or Z1.

First of all, the encoding will have nothing to do with what Justin is experiencing as "juddery" motion. He would see the same thing under the same circumstances even if the footage was shot in 720P24 on HVX200 with DVCPROHD. True 24P is 24P, and assuming a shutter above 1/48th is used the motion will exactly mimic that of a motion picture film camera.

2nd, there is never a field in 720P - everything is always progressive frames.

3rd, the HD100 does not capture 60 fields per second and then combine them into 24P, 25P or 30P. That is the way some 1080i HDV cameras out there work, but not the HD100 (or any other camera in the JVC ProHD famiy.)
The HD100 only clocks at 60Hz (60 FRAMES per second) when in 30P mode.
In 24P mode the sensor clocks at 48Hz, sampling the full 1280x720 CCD 48 frames per second, with each frame exposing for the amount of time determined in shutter setting. If motion smooth is turned off, every other frame is simply discarded by the encoder and only 24fps are encoded to tape. The frames are encoded as a 720p60 stream for HDTV compatibility, but the extra frames required for the pulldown are only written as instructions to "repeat" the pulldown frames during playback and are not included as part of the encoded GOP. This makes the ProHD method very efficient, yet backwards compatible.

BTW, when Motion Smooth is turned on, the encoder takes those 48 sampled frames and combines sequential pairs of frames. This means that each frame now represents 2 frames mixed by visual superimposition, NOT INTERLACING.
Personally, I think Motion Smoothing is just a gimmick that should be avoided at all costs. If that is the look you want, 1/24th shutter will probably give you better results, as well as an extra stop of exposure.

Quote:
Originally Posted by Justin Sabo
But, my question relates to if I have the camera on a tripod and am shooting something moving in the frame, it looks just as juddery. For example, I tested it last night with my pool table. The image quality is amazing and brings out the colors in the balls brilliantly, but when they move it looks bad. I've seen countless movies where pool balls and other objects are moving really fast but don't seem to look like what I shot.
Hi Justin, welcome to dvinfo.

My first question is "how are you viewing the material you shot?" If it is on a computer LCD screen, using a software based player then you can't truly assess HD motion. Make sure you are viewing on a HDTV. Preferably, use the camera for playback and make sure that your TV input setting (1080i/720P) matches the cameras playback setting.

The HD100, when used with a 1/48th shutter, captures motion EXACTLY like a film camera. We've had discussions around here before about why, even though true progressive 24P cameras capture the same temporal motion as film cameras, some people tend to see more "judder" with HD originated material.
One theory that we seem to agree on here is that the difference in depth of field affects the way our brains perceive the motion.
You brought up how great Taylor Wigton's Music Video looks, which is interesting because the video starts with a lateral dolly move, but doesn't seem to "judder." If you look closely you'll notice that the depth of field is very short because of the use of a 35mm adapter (M2.) The background is out of focus and our eyes (and brains) focus on the woman's feet, not the BG. It would be very interesting to perform a comparison test of a similar pan without a 35mm adapter to prove this theory.

Film has been around for over a century and nobody seems to complain too much about the "low" temporal rate of 24fps.
I think the general panning speed rules for film still apply to 24P, but you should also be aware of the FG subject. The only time you see pans without a forground subject in feature films is when we are establishing a large location (mountains, cityscape, etc.) However, these pans are always slow. Fast pans and stedicam tracking shots always have a FG subject for the viewer to focus on. This combined with proper focus and a manageable depth of field help the viewer focus on the subject and not what is going on in the BG.

So Justin, if you really want to know if the material you shot is in any way different from film, I recommend you downconvert your pool table footage to 480P24, burn a DVD, and then watch it on your TV and compare it with a film like "The Color of Money" and see if there really is a difference.
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Old January 5th, 2007, 08:33 AM   #9
 
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thanx Tim and Stephan...I stand corrected. It's good that I was wrong....thank God I'm wrong! I thought I had read that the HD110 sensor capture was a fixed 60fps. Apparently not so. I know there are not "fields" in progressive video, but, it seemed appropriate term for my explanation. Once again, thanx for correcting me. I had the same problem as Justin, so, it seems you've identified the problem. I guess the incorrect default shutter speed causes nyquist artifacts. I need to reshoot my footage with the correct shutter speed to see if it's better. Damn that judder was ugly. I bought the HD110 primarily because it was true progressive scan video. I was disappointed when I thought it played games with the frame processing. Thanx again.

Last edited by Bill Ravens; January 5th, 2007 at 01:30 PM.
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Old January 5th, 2007, 12:48 PM   #10
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Tim, just a question. When viewing the camera on an HD monitor via the component out in 24p I notice that the motion is a bit more "juddery" than it looks when captured in my NLE, and in the final output.

My understanding is that In HDV mode it outputs 60p through the component outs regardless of 24p or 30p mode. Is this right? Does this give it a bit more "judder"?

Regardless, 24p shot with this puppy looks great in my NLE and upon rendered output. Monitoring through the component out tends to to be a bit more "juddery", at least that has been my experience.
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