Flat-Panel HDTV Choices: LCD vs. Plasma HDTV – Part 3 (Response Time, Refresh Rate and Frame Rate)
Currently, flat TVs are created using two different technologies: plasma HDTV and Liquid Crystal Display (LCD) HDTV. The foundation of the plasma TV is over a million tiny glass cells that are charged with a mixture of neon and xenon. Behind these cells are colored phosphors, which are chemical compounds that emit light when energized. Each cell has three phosphors; one red, one blue, and one green. When activated by an electrode, the plasma cells emit invisible UV light. The UV light strikes the red, green and blue phosphors on the back of the display and thus creates the pixels that form the image you see on the screen. LCD (Liquid Crystal Display) technology works differently. Liquid is suspended between two transparent panels. Within the liquid are crystals that, when activated by voltage, re-position themselves so that they either allow the light to pass through the panel and or block the light. This process is similar to turning on and off a million light bulbs. Fluorescent tubes behind the panels supply the light source. Both the lit and unlit crystals create visible pixels that cumulatively compose the image on the screen.
The others issues are Response Time, Refresh Rate and Frame Rate.
Response Time and Refresh Rate: These two attributes work together to determine how fast a moving picture a panel can reproduces without blurring the image. Response time measures how fast a panel can make changes on the screen from the time an input is received. It used to be the case couple years back that LCD panels had slow response times, and response time was the limiting factor causing motion blur on these sets. That’s because LCD technology requires each pixel to go from an on state, to an off state to back on in order to refresh an image.
Panel response times have by now been improved enough that the actual response time is no longer a limiting factor, and to the extent that motion blur still exists with LCD sets, it’s a function of the refresh rate, or the frame rate. LCDs have until now had frame rates of 60 frames per second, which is the same rate found in native SDTV and HDTV signals. In 2007, the main manufacturers of LCD HDTVs will all be producing high end lines of panels with a 120 Hz refresh rate that will make up any motion blur gap LCD may have had in the past. Since the signal itself is only 60 Hz (or frames per second) the additional frames are being filled in with signal processing software which interpolates what the extra frames should look like. The results are moving pictures that loose little to no definition at all. When you see it, we think you’ll agree that it’s really pretty darn cool. To get this new technology, you’ll have to pay more for an HDTV. For now, Plasma has a slight margin over most LCDs for motion response. Toward the end of 2007, LCD will be just as good–and in some cases better–at displaying fast images, but not for the same price as plasma. However, at the higher price of a 120 frame rate LCD, you’ll also get full 1080p resolution, and an expanded color gamut.
Frame Rates: It’s generally accepted by most viewers that film images look better than TV images. In one key respect, TV actually has an advantage over film, and that is in the frame rate. TV and video signals (both SD and HD) use a frame rate of 60 frames per second, whereas film is all shot at 24 frames per second. A problem arises when you convert content shot on film for viewing on TVs or HDTVs. To fit the 24 frame per second content into the 60 frame standard of TV, a process called 3:2 pulldown is used. Some frames get duplicated 3 times, and some get duplicated 2 times to make the fit. Without some really good image processing to interpolate intermediate steps and remove artifacts, this process can result in jerky movement. Advances coming out this year from a couple of the big HDTV manufacturers address the problem in a couple different ways. One way will be to eliminate 3:2 altogether and offer TVs capable of a 24 frame setting which can detect film originated content, remove the 3:2 duplicate frames and display the content in 24 frames just like you were watching a film. Another method will use interpolated frames instead of 3:2 duplicates to produce a smooth transition between frames, and still show at the great 60 frames per second. These new technologies should be available in the second half of 2007 on high end LCD and plasma models.
- Related Post :
- Flat-Panel HDTV Choices: LCD vs. Plasma HDTV – Part 1 (Picture Quality, Price, and Power Consumption)
- Flat-Panel HDTV Choices: LCD vs. Plasma HDTV – Part 2 (Contras Ratio, Color Gamut, and Resolution)
- Flat-Panel HDTV Choices: LCD vs. Plasma HDTV – Part 4 (Image Processing, Screen Burn-In, and High Altitude)
- First JVC HDTV with 120Hz Refresh Rate
- What Different of DLP, Plasma TVs, LCD, and HDTV
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