Talya wrote:
Lenas wrote:
Not true. If a TV has a refresh rate of 60hz, it's always moving at 60hz. To display 30fps on a TV with a 60hz refresh, each frame is repeated 2 times every 30th of a second. TV's don't look for changes in the frames before they do anything.
You don't understand.
With a CRT, the redrawing of the screen was necessary. The pixels on the screen stopped glowing in tiny fractions of a second if they weren't being hit by that electron gun.
On an LCD, to actually redraw a screen, all pixels have to be turned off, then turned on again. The pixels are all represented by an individual transistor that is either on, or off. (actually, by several transistors that are on or off, to account for color as well, but that gets complicated, so we'll keep it simple.)
A 120Hz refresh rate on an LCD monitor just indicates that it can change the value of the transistors controlling that pixel 120 times in a second. However, it
does not do so, unless the actual value of that pixel is supposed to change 120 times in a second. If a particular pixel is to remain white for several seconds because the scene on the screen is not changing, then the pixel simply stays on the entire time. The LCD television does not redraw it at all. To do so would actually
lower image quality, since it would introduce an imperceptible flicker as the pixel rapidly shut off and on again. It would also be less accurate, as the pixel would shut off while it was still supposed to be on, and a liquid crystal display can remain in its same state indefinitely without needing a redraw.
LCD screen changes are "incremental" because parts that don't change do not need to be redrawn -- to do so would be a bad thing. A static image is just that -- a static image. The TV is not so stupid as to turn the picture off and on again when it's not changing. The refresh rate of an LCD monitor, at least for non-interlaced resolutions, only indicates the speed at which the screen can adjust individual pixels. The concept of "refresh" is really a misleading term to use on them. Switches that are already on do not get turned off and back on again, nor can they be turned on when they are already on.
120 Hz LCD displays are 120 Hz for a reason. They display each frame (assuming a 24 fps Bluray movie) 5 times within each 24th of a second. This is in an effort to eliminate motion blur. Yes, the image may not actually change that often, but it doesn't change the fact that it is being displayed and/or updated faster than 24 fps.
I totally get what you are saying, it doesn't necessarily re-draw the entire screen, unless the particular frame it is displaying requires it to do so. But that doesn't change the fact that the TV is attempting to update the image at a faster rate than traditional 24 fps. And the 120 Hz / 240 Hz technology TV's were made specifically to eliminate a problem with lower refresh rates. So you can't really say that refresh rates and fps are the same thing in LCD TV's because a 24 fps movie really is displayed at 120 Hz. Yes, there are still only 24 separate frames displayed every second, but they are being displayed multiple times, depending on the refresh rate.
Many high-end LCD televisions now have a 120 or 240 Hz (current and former NTSC countries) or 100 or 200 Hz (PAL/SECAM countries) refresh rate. The rate of 120 was chosen as the least common multiple of 24 frame/s (cinema) and 30 frame/s (NTSC TV), and allows for less distortion when movies are viewed due to the elimination of telecine (3:2 pulldown). These higher refresh rates are most effective from a 24p-source video output (e.g. Blu-ray Disc), and/or scenes of fast motion.
from the same wiki article:
Quote:
The refresh rate is the number of times in a second that display hardware draws the data. This is distinct from the measure of frame rate in that the refresh rate includes the repeated drawing of identical frames, while frame rate measures how often a video source can feed an entire frame of new data to a display.
And another one for good measure:
Most TV sets today refresh the picture either 50 times per second (50Hz) or 60 times per second (60Hz) depending where in the world you live (different regions use different color formatting.) That rate is fine for most images, but when it comes to fast moving shows like sports events the images can appear blurry on an LCD (liquid crystal display) TV. Doubling the rate at which images are displayed, to 100 or 120 frames per second, makes for a better, more high-definition picture.
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