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30 vs 60 frames per second I always thought the human eye could detect no more than 30 frames/sec. Am I missing something, or what's the point of 60fps?
asked by John Fields on August 26, 2009
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Here's the problem. Because a pocket video camera like the Zi6 and Zi8 uses a shutter speed faster than what is common in a film type motion picture camera, the video image is made up of individual still shots (photographic frames on movie film) which in playback at 30 fps are not sufficiently blurred due to subject motion to provide a smooth transition from shot to shot. And so you get a visible jumping effect between these still shots. It's also present at 60 fps, but because twice as many shots are made in a given length of time, the jumping is only half as apparent, giving the impression of much smoother action. Remember that all a video camera is doing is shooting still photos in very quick succession. If you look at the individual frames in a length of motion picture film, which are also "still shots" in their own right, you'll see that it is rare to find a frame that is not blurred due to subject movement. Yet when we see the action projected on the screen, that blurring is not detectable. In fact, the subject looks quite sharp, it's just moving quickly past the lens. The reason we don't notice this is that the same thing happens before our eyes in everyday life, and we are used to it. If someone runs past you, and your eyes aren't panning with him, there is motion blurring, but you don't notice it. It's what we're used to seeing from birth.

The bottom line for me is that my new Zi8 shooting at 1080p/30fps still produces the same jumpy motion as my Zi6 did at 720p/30fps. Since I shoot a lot of action (and after all, aren't "movies" for movement?) The 1080p results I'm getting are unacceptable. What I have discovered, though, is that not only does the problem disappear when I use the Zi8's 720p/60fps setting, but the 720 movies are actually sharper and more pleasing to watch! Comparing the Zi6's and Zi8's 720p/60fps results side by side, the Zi8's are considerably better. So while I won't be using 1080p, 720p/60 works great for my purposes. Much sharper and more natural action.

One weird thing: All the settings on the Zi8 other than 1080p have a wider focal length, wider even than all settings on the Zi6. I don't know why they did this, but if I notch up the digital zoom slightly so that the focal length at 720 matches the Zi8's 1080 FL and all the Zi6's settings, the Zi8 images produced at 720p/60 exceed in quality those at 1080p, and that's with a static subject. Amazing, but true.

So I'm happy with the Zi8 at 720/60. It's a big improvement over the Zi6. But I'm still not sold on color accuracy. Initial indoor comparisons seem to favor the Zi6 for richness and fidelity of color, although admittedly there's a lot more noise in the Zi6 image. I have yet to do tests outdoors on a sunny day. That should be the clincher or the deal breaker, whether to keep my Zi6 or shelve it in favor of the Zi8 as my primary pocket video camera. PS Another thing that I'm worried about, at least initially, is that the rechargeable battery seems to have a shorter life than the AA's in the Zi6. I hope I'm wrong about that.

UPDATE: I have now used the Zi8 outdoors and have a new perspective on the camera's 1080p/30 and 720p/60 modes. 1080p did very well outdoors in bright sunlight, whereas it seemed to have suffered indoors, at least in comparison with 720p. Outdoors, 720/60 produces roughly the same result as it does in the Zi6; and the Zi8's 1080/30 did indeed produce a sharper image, but the frame to frame jumping effect was noticeable. I took the camera to an amusement park with two active 11-year-olds and tried to plan ahead at each attraction as to which mode to use. It turned out that 1080 was usually the best choice, at least in part because of its longer focal length. To get closeups of the boys with 720 I had to use more digital zoom, thus decreasing sharpness. But if I used 1080, that was not so much of a problem. In many cases I was able to get "close" enough without the need for any zoom, and the images are very sharp in the bright sunlight. Of course the 30fps frame jumping is there as well; however, it isn't always as noticeable. It depends on the subject and degree of action and, for me at least, isn't predictable ahead of time. One thing that's good about the 1080p mode is that if you plan to search out individual frames later for the best still shot, you will have a nice usable still to print on 4x6 or 5x7 paper. Sometimes, living with frame jumping in the moving image may be an acceptable sacrifice for the sake of being able to get some nice stills out of it. You sure have a ton of "poses" to choose from!

As for color reproduction, the Zi8 seems to be virtually perfect outdoors...accurate, not saturated, very natural in appearance. The only problem I had at the amusement park was when I was filming one of the boys at a game where he was standing in the sun and throwing baseballs into the shade (trying to break white plates against a black wall). I was panning back and forth between him and the plates. The camera adjusts quickly to changes in brightness, but a few times it got confused and overexposed the boy because of the dark background. When I brought him into the center of the frame he did become correctly exposed, but there was a definite pause while the camera "figured it out."

Bottom line: The choice between the 1080 and 720 modes is going to be subjective. Obviously the only way to get your own personal slant on this is to try the camera and decide for yourself. It's possible that for some people the 1080p/30fps mode will work fine in all situations. Overall, the Kodak Zi8 is a very nice pocket video camera that I believe will satisfy just about everyone. If it were possible, I would change my rating to four stars instead of three.
David answered on September 3, 2009
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There are two physiological phenomena that come into play. One is the "illusion of motion," in which the brain begins to perceive rapidly replaced individual images as one moving image. In motion pictures this takes place approximately between 15 and 18 frames per second or higher, depending on variables. The second, "persistence of vision," has to do with the tendency of the retina to retain an infusion of light. It also varies, but is higher than the illusion of motion. If images, or any lights, are alternately flashed on and off below a certain frequency we see flickering of that light or image--very annoying. But if the image is flashed at a speed above that necessary for the retina to retain the infusion of light, then we no longer see flickering, but rather the illusion of a constant intensity of light. The threshold of this effect is generally in the neighborhood of 60 to 75 times a second, which is the reason that motion picture frames are flashed onto the screen a the rate of two or three times each before proceeding on to the next frame. Obviously, three is better. A three-bladed shutter wheel between the lamp and the film accomplishes this. In video this is why 30 fps interlaced and 60 fps progressive give the same degree, or lack of, flickering. Persistence of vision also comes into play with the refresh rate of our computer screens. Most that I've seen are set at 75 or higher.
David answered on September 4, 2009
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Thank you David Simon for your in depth analysis. It sucks that the Zi8 doesn't have it's standard definition also set at 60 fps for my liking since I will not be burning any footage to Blu Ray anytime soon and will be burning to DVD. Sure it's great watching 720p on a High Def TV by connecting to HDMI, but eventually the data will be sent to my hardrive for safe keeping and burning a DVD copy to play on a stand alone player is key for me. For sure though, I'll be using the 720p @ 60fps mode in the near future, ( when I get a Blu-Ray writer, or when I get a high end comp that can handle Hi Def video editing) until then SD quality for me lol.
Gerard J. Duya answered on September 9, 2009
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Replaying at 60fps wouldn't make a big difference from 30fps. But being to record at 60fps can be very handy in some situations such as recording a fast moving child.
Kali76 answered on August 26, 2009
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I may have some details wrong, but I think minimum for motion is 18 fps, film is 24 fps, normal television 30fps. 60fps will just seem a little smoother (also depends on shutter speed). BUT with 60fps you can do much better slow motion, and you can resample to 24fps.
rocketscience answered on August 31, 2009
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If you are planning to do a transfer to film, which is preferable, 1080/30, 720/60, or 720/30?
Jerry Kokich answered on January 24, 2010
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rocketscience is on the right track. alot of internet video is as low as 15fps. film is traditionally 24fps. broadcast tv is approx. 30fps (interlaced). it is effectively impossible to resample from 30p to 24p smoothly, but it is possible to go from 60p or 60i to 24p.
as for trying to reproduce what the human eye can see, you would be looking for somewhere around 4000 lines of horizontal resolution at 60fps progressive, and it would have to be uncompressed, of course. this is not the kind of technology you can fit in your pocket (at least not today and not with a consumer budget).
jerry, the ideal camcorder footage to transfer to film would be 1080/24, but no footage shot on a $200 camera would be worth transferring to film because the cost of the transfer would be better spent on a better camcorder.
A. Pickett answered on April 6, 2010
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Now, that, spending more money on the camcorder instead of the transfer, makes a lot of sense, since the connotation is that is would be far less costly. As I'm sure you know, the worst phrase to use on a shoot is "We'll fix it in post." Thank you for your comments; all this info is really helping!

Any suggestions as to what con or prosumer camera (keeping in mind cost, of course) to use? I am not married to any one brand as the tech is fairly similar between them all, I would think, but there are advantages to some, I;m sure.
Jerry Kokich answered on April 6, 2010
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