All about Contrast Ratio in Plasma and LCD Screens
October 3, 2008
What is Contrast ratio?
Contrast Ratio is the difference between the light intensity of the darkest black and the brightest white. Quality of the video picture depends greatly on the contrast ratio rendered by the device. Television sets that come with high contrast ratio produce dark scenes with black colour and shadow detail information. And televisions that come with low contrast ratio do not produce black areas over dark scenes, instead they produce grey surface over black areas that makes the pictures look totally flat and dull. Levels of contrast ratio, varies with different manufacturers and thus necessitate the consumers to be cautious, while in the process of choosing a television with such contrast levels.
Plasma TVs are built with better contrast ratio than the LCD TVs. Each pixel in plasma screen emits its own light and thus it becomes necessary for only the brighter parts to be lit making the darker areas more darker, while in the case of an LCD screen, its individual pixels block the back light to darken them. Hence, the pixels fails in reproducing the perfect black. Static Contrast Ratio is defined as the luminosity of the brightest and the darkest colours, the system is capable of producing at any instance of time, simultaneously. And Dynamic Contrast Ratio is defined as the ratio of the luminosity of the darkest and brightest colour, a system is capable of producing over time. Contrast ratio is the capacity of producing the darkest and brightest colour and this is also expressed as light intensities.
Ways of measuring Contrast Ratio
Though, a number of manufacturers adopt their own methods for measuring contrast ratio, many others follow a different method. Some people measure contrast ratio of a television in a room, where the light emitted by the TV does not get reflected by taking into account the time, this light gets completely absorbed.
The two main method of measuring contrast ratio are the ANSI Contrast Ratio measurement and Full On/Off Contrast Ratio measurement. In the latter type, it is the output-ratio of the light of a full white image and the light output of a full black image. This method is mostly practised by the manufactures as it yields typically 25% more, than the former method of measurement; the ANSI contrast measurement.
ANSI Contrast Ratio is a method of measuring the contrast ratio by taking the conditions of the room into consideration. To determine the ANSI Contrast ratio, a pattern of alternate black and white box or a checker board pattern is used. Here, contrast ratio is measured as the average light output from the white boxes divided by the average light output from the black ones. You can also follow this simple method of illuminating the wall behind the screen to make the darker areas appear darker.
Whatever be the method of test followed, there always emerged a sort of disagreement regarding the contrast ratio, because the contrast ratio measured by the manufacturers would, however be slightly different from that of the viewer, when he starts using the TV.
Higher the better
Plasma displays that come with higher contrast ratio produces dark portions that appear darker and bright portions appearing brighter. Plasma TVs that come with a contrast ratio of 5000:1 or higher, provide better viewing experience depending upon the screen size of the TVs. Higher contrast ratio also delivers greater gray values in between pictures. A contrast ratio of 5000:1 determines that the display device is capable of displaying the black level 5000 times darker than the white.
Conclusion
The concept that higher contrast ratios offer better quality may be a bit misleading if it is mentioned in a wrong sense or misused. Big numbers may mislead you by culminating into noise-stricken images with increased details, often more than the desired levels, and hence it is utmost important to be cautious with these ratings.
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