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• #50 9950es aktív tag lenox #47

  Új Válasz 2010-03-18 17:51:57 #50

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  Na, LCD, jön a wall of text, ugye 2007-ben a 120hz volt a mérce:
  The integer ratio that you mentioned—120=5×24=2×60—is not the primary driver behind the claim that 120 Hz provides a better image. This high-frame-rate driving is being proposed as a solution to the so-called perceptual-blur problem of the LCD. The LCD has two major blurring mechanisms, one of which is physical and the other of which is perceptual. The physical mechanism is the inertia in the motion of the liquid-crystal molecules that are being rotated to reduce or increase the amount of light that is allowed to pass through. The inertia leads to the molecule's not reaching its desired position within a frame time, and this slow 'dynamic response' leads to moving images that appear washed out. This problem is most acute with small changes in gray scale that require small changes in the position of the molecules. This issue has been largely overcome through a mechanism called overdrive, in which the LCD electronics store the current image and use knowledge of the current value at each pixel, versus the value desired in the next frame, and accordingly apply a compensated drive that is higher or lower, so that the pixel reaches the desired value within the next frame time. You can see that new LCD TVs report 'gray-to-gray' response times of 8 msec or less.

  Aside from this physical mechanism, an additional source of blurring is the fact that LCDs are so-called scan-and-hold, or 'always-on,' displays, where the image is visible on the screen throughout each frame time, unlike emissive displays, such as the CRT, PDP [plasma-display panel], or OLED [organic light-emitting diode], where there is a dark period. This always-on behavior conflicts with the way the human eye tracks and perceives motion. The eye works best when presented with a series of images with a dark period in between. For example, in a movie theater, a viewer's eyes track an object of interest as it appears in consecutive frames and fills in the image of its intermediate points during the intervening dark periods. In the case of an always-on display, such as an LCD, the moving object appears to stay in one place and then jump to the new location. The disparity between the fixed location of the object and the intermediate position that the eye expects to see leads to the perception of blurring. There are various ways of solving this problem, and it is a very active research area, but the currently most favored approach is to interpolate new frames and run the display at a higher frame rate, so that the jumps in the moving object are much smaller. There is nothing magical about 120 Hz except that the integer ratio that it has with 60 and 24 Hz makes it a convenient number from the perspective of various commonly used motion-compensated frame-interpolation algorithms.

  What is the reality behind the marketing hype? There is no doubt that one can be made to see the differences between a 60-Hz LCD and a 120-Hz LCD. The simplest demo is done with a horizontally scrolling image, where you can see a major difference in the sharpness of various vertically oriented edges. The difference is less perceptible for real video and film because in the scenes that have motion, the edges of most moving objects suffer from optical motion blur, and the presence or absence of perceptual blur is less visible. However, in cases where there is a single major object of interest that the camera is closely tracking the camera, the difference between 60 and 120 Hz is apparent. In other words, I can certainly create demo material to show you the value of a good 120-Hz display versus a standard 60-Hz display.

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