Flat Panel LCD TFT
Twisted Nematic In The Flat Panel LCD TFT
tft lcd
In the previous article of Flat panel LCD TFT, A Brief of TFT LCD Panel explained how a Thin Film Transistor works in the small and large displays. In this article, it explains about Twisted Nematic and how it is used.
Twisted Nematic + Film (TN+Film) display is the most common consumer display type. The pixel response time on modern TN panels is sufficiently fast to avoid the shadow-trail and ghosting artifacts of earlier Flat Panel LCD TFT production. The fast response time has been emphasised in advertising TN displays, with note in most cases this number does not reflect performance across the entire range of possible color transitions.
Response times were quoted for an ISO standard black-to-white transition and did not reflect the speed of much more common transitions from one shade of grey to another. More recent use of RTC (Response Time Compensation – Overdrive) technologies has allowed manufacturers to significantly reduce grey-to-grey (G2G) transitions, without significantly improving the ISO response time. Response times are now quoted in G2G figures, with 4ms and 2ms now being commonplace for Twisted Nematic Film based models. No wonder, the good response time and low cost has led to the dominance of TN in the consumer market.
The Twisted Nematic display suffers from limited viewing angles, especially in the vertical direction. For colour representation many panels use 6 bits per colour, instead of 8, and are consequently unable to display the full 24-bit truecolor (16.7 million colour shades) available from modern graphics cards. These panels can display interpolated 24-bit color using a dithering method which combines adjacent pixels to simulate the desired shade. Beside dithering method, they also use FRC (Frame Rate Control) as color simulation, which quickly cycles pixels over time to simulate a given shade. These color simulation methods are noticeable to most people and bother to some FRC tends to be most noticeable in darker tones, while dithering appears to make the individual pixels of the LCD visible. Overall, color reproduction and linearity on TN panels is poor.
The factors why laptop displays can’t be reused directly with an ordinary computer graphics card or as a television, is mainly because it lacks a hardware rescaler (often using some discrete cosine transform) that can resize the image to fit the native resolution
The raw Flat Panel LCD TFT is usually factory-sorted into three categories, with regard to the number of dead pixels, backlight evenness and general product quality. Additionally, there may be up to +/- 2ms maximum response time differences between individual panels that came off the same assembly line on the same day. The poorest-performing screens are then sold to no-name vendors or used in “value” TFT monitors (often marked with letter V behind the type number), the medium performers are incorporated in gamer-oriented or home office bound TFT displays (sometimes marked with the capital letter S), and the best screens are usually reserved for use in “professional” grade TFT monitors (often marked with letter P or S after their type number).
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