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30 Frames per Second vs. 60 Frames per Second |
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| A Technical Overview |
60 frames per second vs. 30 frames per second has been one of the most contested ideas around the web and in print for the last year. Today we will look to see who is right, who is wrong, and who is just plain confused.
Chipmaker (and now boardmaker) 3dfx has been evangelizing gaming at 60 fps since the Voodoo 2 was released. Many have looked down upon 3dfx for this due to the common misconception that humans cannot distinguish framerates over 30 fps, so what is the point of having visuals running at 60 fps? Misconception you say? Yes. In this article we will look behind the technology of games, computers, movies, and television and the physiology and neuro-ethology of the human visual system. |
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| Movies |
I have seen film students write in to columns about how anything over 24 fps is wasted. Why 24 fps? Movies in theaters run at 24 fps. They seem pretty smooth to me, so why would we need more? Well, let's take a look at movies from the eyes' perspective. First off, you are sitting in a dark movie theater and the projector is flashing a really bright light on a highly reflective screen. What does this do? Have you ever had a doctor flash a bright light in your eye to look at your retina? Most of us have. What happens? A thing called "afterimage". When the doctor turns off the bright light, you see an afterimage of the light (and it is not real comfortable). Movie theaters do the same thing. The light reflected off the screen is much brighter than the theater surroundings. You get an afterimage of the screen after the frame is passed on, so the next frame change is not as noticable.
Screen refresh is also a very important factor in this equation. Unlike a television or a computer monitor, the movie theater screen is refreshed all at once (the entire frame is instantly projected and not drawn line for line horizontally as in a TV or monitor). So every frame is projected in its entirety all at once. This then leads back to afterimage due to the large neurotransmitter release in the retina.
Perhaps the most important factor in the theater is the artifact known as "motion blur". Motion blur is the main reason why movies can be shown at 24 fps, therefore saving Hollywood money by not having to make the film any longer than possible (30 fps for a full feature film would be approximately 20% longer than a film shown at 24 fps, that turns out to be a lot of money). What motion blur does is give the impression of more intervening frames between the two actual frames. If you stop a movie during a high action scene with lots of movement, the scene that you will see will have a lot of blur, and any person or thing will be almost unrecognizable with highly blury detail. When it is played at full 24 fps, things again look good and sharp. The human eye is used to motion blur (later on that phenomena) so the movie looks fine and sharp. |
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| TV, Video Tape, and DVD |
TV's run at a refresh rate of 60 Hz. This is not bad for viewing due to the distance we usually sit from the TV, and the size of the phosphors on your average set and the distance between phosphors (between .39 for a high end one, to .5 and higher for cheaper models). This is actually quite big and fuzzy for most of us, but as long as we are not doing any kind of productivity software (such as word processing) and just watching movies at least 6 feet from the TV, that is just fine.
Now TV transmissions, video tape, and DVD play at 30 fps. The increase from movies is due mostly to the environment that the TV is watched in. It is usually quite a bit brighter than in a movie theater, and most importantly a TV does not do a full screen refresh, rather each frame is drawn line by line horizontally by an electron gun hitting the phosphors in the screen. So basically each frame is drawn twice by the TV (60 refreshes per second, 30 frames per second). Now because the frame rate is * the refresh, transitions between frames go a lot smoother than if you had say a 72 Hz refresh and a movie playing at 30 fps. Don't ask me why, it is due to wave behavior, which is higher level physics, and I can't go into that without making this a 30 page paper. Needless to say, the physics behind this make video and DVD look very smooth.
Motion blur again is a very important part to making videos look seamless. With motion blur, those two refreshes per frame give the impression of two frames to our eyes. This makes a really well encoded DVD look absolutely incredible. Another factor to consider is that neither movies or videos dip in frame rate when it comes to complex scenes. With no frame rate drops, the action is again seamless. | |
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