Caltrops - Reviews





	[quote name="Jerry Whorebach"][quote name="<a href="http://www.techmind.org/lcd/">W.A. Steer, PhD</a>"]<b>Refresh rate, response time, flicker and motion-blur</b> There seems to be a lot of confusion and mis-information on these topics on the web; here's my clarification... <b>Refresh rate</b> is the rate at which the electronics in the monitor addresses (updates) the brightness of the pixels on the screen (typically 60 to 75Hz). For each pixel, an LCD monitor maintains a constant light output from one addressing cycle to the next (sometimes referred to as 'sample-and-hold'), so the display has no refresh-dependent flicker. <i>There should be no need to set a high refresh rate to avoid flicker on an LCD.</i> <b>Response time</b> relates to the time taken for the light throughput of a pixel to fully react to a change in its electrically-programmed brightness. The viscosity of the liquid-crystal material means it takes a finite time to reorientate in response to a changed electric field. A second effect (which has a rather more complicated explanation) is that the capacitance of the LC material is affected by the molecule alignment, and so if a step change is brightness is programmed, as the LC realigns the cell voltage changes and the brightness to which it settles is not quite what was programmed. Unless 'overdrive' (which tries to pre-compensate for this effect) is employed, it may take several refreshes before the light output stablises to the correct value. Response rate for dark-to-light is normally different from light-to-dark, and is often slower still between mid-greys. VESA and others define standard ways of measuring response time, but a single figure rarely tells the whole story. <i>Manufacturers 'response times' rarely tell the whole story. Unless combined with a strobing backlight, response times much below 16ms are likely to be of only marginal benefit, owing to more-dominant 'sample and hold' effects (see below),</i> The visual effect of <b>motion blur</b> is self-explanatory and it is fairly intuitive to realise that a slow pixel response-time will cause this problem. What is less obvious, but at least as important in causing motion-blur, is the 'sample-and-hold' effect: an image held on the screen for the duration of a frame-time blurs on the retina as the eye tracks the (average) motion from one frame to the next. By comparison, as the electron beam sweeps the surface of a cathode ray tube, it lights any given part of the screen only for a miniscule fraction of the frame time. It's a bit like comparing film or video footage shot with low- and high-shutter speeds. Motion-blur originating from sample-and-hold in the display can become less of an issue as the frame (refresh) rate is increased... <i>provided that the source material (film, video, or game) contains that many unique frames.</i> For LCD TV there is significant interest in the industry in strobing (flickering!) of the backlight deliberately so as to reduce sample-and-hold motion-blur; the manuafacturers have various tradenames for this, including Samsung's LED motion plus, Philips' ClearLCD scanning led backlight, etc.[/quote] I like the shutter speed analogy in the last paragraph. If you take nothing else away from this, at least try to understand that part.[/quote]