First Impression; serious drawbacks

Alan Roberts makes an awesome observation over on the dvdoctor thread -- that if you're viewing it on a computer, it's going to obviously and always involve a frame-rate conversion -- and frame rate conversions introduce judder. A television or proper video monitor will change its scan rate to match the frequency of the incoming signal (either 24Hz, or 50Hz, or 60Hz) but a computer monitor will always run at whatever refresh rate it's set to run at -- typically 60Hz or 72Hz. So when you watch video on a computer screen, there's usually (if not always) going to be a scan rate conversion happening -- and that will introduce juddering and unnatural rhythms into the video. And one reason that 25p folks might be noticing this more than our 24P brethren, is that 24p easily goes into 72Hz (no frame rate conversion necessary) and 24p on 60Hz looks just like what we're used to always seeing anyway. Whereas 25p on 60Hz or 72Hz doesn't work, and results in the computer having to synthesize an unnatural pulldown sequence.

I reiterate -- the absolutely only way to test for whether there is an issue with the camera or not, is to watch the footage from the playback of the camera, on an appropriate VIDEO monitor. And play back from the camera, not from a PS3, because also in the dvdoctor thread, there is a statement made that the PS3 does an internal standards conversion from 25p/50hz to 60Hz. So plug the camera into a monitor and look at it there. If it looks good there, then the footage is good. If you have computer issues that are causing jerkiness and strobing and whatnot, well, those are, by definition, computer issues.
 
Although, it should be noted that a lot of modern TV screens don't run at 24p either. In fact, a coworker was very distraught over the judder issues in EVERY flat panel she tried, including 120Hz models. They up-convert as well, and not all upconverting is created equal. CRT displays are WAY more forgiving in my eye to source content.
 
Okay, I just ran a test using the AF100 vs. the HMC150. The idea here was to get two 24p cameras, of different technology (one CCD, one CMOS). Ideally I'd have two of different makes, but hey, I've only got what I've got here to work with. And with them both being AVCCAM, I could play them both back from one camera (which is vital, as you will see).

I set them up side by side, framed and focused and exposed exactly the same on a target (a mostly-blown-out window, plus I stuck a black card on the side of the window so I would have the ultimate in contrast to compare it to).

Sync'ed 'em up and ran them side by side, back and forth, panning at different frequencies.

Then, for playback, I played back from the AF100, using HD-SDI with 24PsF, into my BT-LH80W monitor which supports 24PsF playback. The point here being, absolutely no pulldown or playback issues would be introduced. No computer issues. No frame-sync issues. No pulldown issues or image tearing or computer graphics cards would be introduced. No blu-ray players or scan conversions. No anything. Just raw 23.976 recorded to the cards, played back from the camera at 23.976fps, through HD-SDI 24PsF, into a 23.976PsF-capable monitor.

The verdict? They're identical. Other than the absolute minorest skew on the fastest pans, they look the same. And stepping through frame by frame, they both look exactly like they should. Noticeable edge juddering in motion? Yep, definitely -- on both of them. Freeze-frame and they look perfectly crisp, perfectly like they should, no weird edge-folding or other nonsense. Stepped frame-by-frame through many frames to see for sure.

My verdict is the same as Alan Roberts - there is no issue here, as far as the recorded footage goes. If there is unnatural jerkiness being introduced into the imaging chain, it's either a) computer-related issues, or b) people being overly sensitive to the inherent stutter that happens on a very high-contrast edge during a pan during a slow-frame-rate capture. In one moment you're seeing black on that edge, in the next microsecond you're seeing white -- that's gonna be visually jarring, no matter what camera it's shot on. Step through frame by frame, and it looks great. But when running it at full speed on a monitor, of course the edges are going to be flashing -- that happens on every camera, and it'll even happen on non-cameras. As an example, I just created this little video file in After Effec ts -- I set up a black and white image, and panned it through the frame, taking seven seconds to go from one edge to the other. I even turned on motion blur. I rendered it out as a 1920x1080 h.264. Play it full-screen, and watch the edges -- they look exactly like how the AF100 renders edges (and how the HMC150 rendered them too).

http://dvxuser.com/barry/AF100/AE-Black-and-white-motion.mp4

As near as I can tell, this is not a camera issue whatsoever, it seems to be a combination of computer/monitor playback issues combined with mismatched expectations of what a very-high-contrast edge should look like in 24p.

As far as I can tell, the AF100 is rendering motion exactly as it's supposed to.
 
Barry_Green said:
If there is unnatural jerkiness being introduced into the imaging chain, it's either a) computer-related issues, or b) people being overly sensitive to the inherent stutter that happens on a very high-contrast edge during a pan during a slow-frame-rate capture. In one moment you're seeing black on that edge, in the next microsecond you're seeing white -- that's gonna be visually jarring, no matter what camera it's shot on. Step through frame by frame, and it looks great. But when running it at full speed on a monitor, of course the edges are going to be flashing...
Click to expand...
Thanks for running these tests, Barry. Your results are consistent with my conclusions about the nature of the edge flickering that I observed on the high-contrast vertical edges in Nugat's video sample:

http://www.four-thirds.org/en/fourthirds/index.html

Although this doesn't appear to be a flaw in the camera itself, I think it does bring up a serious issue in video production. Unlike still photography, where high-contrast, fine-resolution optics are always desirable, high quality moving pictures require seamless visual continuity between frames. One reason fast shutter speeds are usually undesirable is because they capture sharply-delineated images that lack natural-looking motion blur. In addition, HD-resolution sensors with progressive scanning can faithfully reproduce distracting details that in earlier times would have been obscured by SD-quality interlaced artifacts and smearing. In some cases it may turn out that the inherent temporal choppiness of 24p video requires adding post-processed edge-smoothing to the HD video workflow.
 
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