What is Dynamic Contrast Ratio?

Those of us that were children back in the dark ages of black and white television (or even colour cathode ray sets) might remember fiddling with the contrast knob on the front of the television to completely grey out the actors at one end of the knob’s reach, and turn them into eyeball-straining black and white monsters at the other end. If you remember that, then you’ve been learning about contrast ratio since you were knee high to a grasshopper! Most of this television features guide will feel like second nature to you.

What is contrast ratio?
On LCD televisions, cathode ray televisions, computer monitors, and any electronic display, contrast ratio measures the difference between the whitest white and the blackest black the display can handle. In technical terms, Cnet describes it as “the ratio of the light level (luminance) the display produces when fed a white signal to the luminance when it’s fed a black signal”. The luminance is measured in candela per square metre (cd/m2). The full on/full off approach to measurement of static or dynamic contrast ratio is usually used, with an all-white screen compared to an all-black screen.

Why is bigger better with contrast ratio?
Having a high contrast ratio LCD television does not mean you have to watch everything in the ‘black and white monster’ view. It measures capability, but not necessarily input luminosity and contrast. If you have a picture coming to the television with a full brightness range of 0% (complete black) to 80% (bright white), and the television’s contrast ratio is fairly low, you might perceive only a portion of that range of brightness.

In English, the pictures start looking a little more greyed out with very low contrast ratios, where blacks are deeper with high contrast ratios. White performance is generally less important to picture quality than black depth. A high contrast ratio will show better detail in scenes with low lighting, because the deepest black contrasts better with slightly lighter objects around it.

There is definitely a limit to necessary contrast ratio, though. At any given moment, many references state that the human eye can perceive up to 10,000:1 contrast ratio. Anything above this in static contrast ratio will be effectively useless. Note that dynamic contrast ratios can be much higher than this, and because your eye can adjust to different lighting conditions, up to 1,000,000:1 in dynamic contrast ratio could be perceived by your eye.

What is dynamic contrast ratio – why is it preferable to static?
LCD television and plasma television manufacturers have been developing methods to improve the contrast ratio of their sets by using dynamic systems. So the backlighting will change according to the scene the television is displaying, to make blacks blacker in low-lit scenes, and whites brighter in high-lit scenes. LCD televisions do this using either a dimmer system for the backlighting, or an expanding and contracting aperture (like in an old-style camera).

How your room affects contrast ratio
When manufacturers measure their LCD televisions’ and plasma televisions’ contrast ratios, they use the ideal viewing environment of a room in total darkness. Ambient light reflects off the screen and reduces the distinction between both colours and black and white contrast, effectively lowering your contrast ratio substantially. You can actually increase your effective, or perceived contrast ratio quite easily … simply by putting up blackout curtains and turning off the lights to watch a movie!

The verdict in numbers
It’s difficult to say what level of dynamic contrast ratio will produce good viewing quality in your LCD television, because every manufacturer measures it differently. The testing methodology is usually not available for review, either! Actual numbers are less important than the fact that a television has dynamic contrast ratio capability, which greatly increases its contrast range. Look for a reputable brand – they are still available at great prices online!

Sources:
http://en.wikipedia.org/wiki/Contrast_ratio
http://news.cnet.com/8301-17938_105-10148015-1.html
http://www.answers.com/topic/contrast-ratio
http://www.wisegeek.com/what-is-the-difference-between-an-hdtvs-dynamic-and-static-contrast-ratio.htm
http://wiki.answers.com/Q/What_contrast_ratio_can_the_Human_eye_perceive&src=ansTT