Contrast ratio of LCD TV - explained
June 24, 2007
The contrast ratio measures the capacity of a display device to produce the brightest colour and the darkest colour and it is usually expressed as a ratio of their light intensities. There is a lot of disagreement prevails in measuring the contrast ratio so the contrast ratio measured using different methods show different figures.
While manufacturers of LCD TV follow their own methods to measure the contrast ratio, most of them are reluctant to take into account the effect of room light conditions. Majority of them have a view that the contrast ratio of a display device like LCD TVs should be measured in an ideal room where there is no place for the light from TV to get reflected and all the light that a TV emits is completely absorbed. They usually prefer the method of the complete on/off when they measure the contrast ratio as it would show the maximum contrast ratio.
There is another method, the Ansi contrast which provides the most realistic ratio as it includes the effects of room into measurement. Ansi contrast is often used to measure static contrast ratio while complete on/off method is employed to measure the dynamic ratio.
The methods used for measuring pure black and white vary from one manufacturer to another. However, all these methods are less likely to give the contrast ratio acceptable by everyone. There is always discrepancy between the contrast ratio specified by the maker and the actual contrast ratio that a viewer discovers after he puts the TV under a test.
Newer LCD TVs use PVA (Patterned Vertical Alignment) and S-PVA (Super Patterned Vertical Alignment) to produce deeper black levels and greater viewing angles. S-PVA also removes ghosting to certain extent by providing fast response times using RTC technologies.
Good black depth is prerequisite for viewing dark scenes in well-lit rooms. PVA and S-PVA technologies enhance the contrast ratio up to 3000:1
Another method a LCD TV uses to offer black depth is by illuminating the wall behind the screen thus making the dark scenes appear darker.
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