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Dynamic Contrast Ratio – Understanding HDTV terms

December 22nd, 2010 Leave a comment Go to comments

Contrast ratio is one among the many factors deciding the successful viewer satisfaction. Due to the market competition, manufacturers are using hyper inflated numbers as a marketing tool to make the customers believe that their product has best specifications. This is especially true for the contrast ratio number. You need to keep a rational approach while reading the Contrast Ratio number in selecting a new HDTV.

In simple words, the contrast ratio measures the capability of your HDTV to display bright and dark portions of the image or movie you are watching – distinctively. For example, while viewing a movie shot with high illumination scenery, the high quality TV can clearly distinguish all the image portions – including the darker potions of the image. The chance for occurring grey blotches on dark portions of image is low in high contrast television display.

Contrast ratio is usually expressed as fractional. A contrast ratio of 100000:1 means the TV can display white portion of the image with luminance 100000 times dark portions of image.

There are two different ways a contrast ratio is expressed – One is dynamic contrast ratio and the other is static contrast ratio. In dynamic contrast ratio the screen is first made completely white and the luminance level is measured. Next, the screen is made completely black and the luminance level is measured again. The ratio of these two numbers is the dynamic contrast ratio.
In static contrast ratio, the TV screen is divided in 16 rectangles with alternate black and white portions. A luminance meter is places in front of the white rectangle and its luminance level is measured. This is repeated for the black rectangle. The ratio of these two numbers is the static contrast ratio. ANSI contrast ratio is static contrast ratio.

Measuring ANSI Contrast ratio

ANSI or static contrast ratio is measured by measuring luninance in front of the black and the wite rectangles in a chekered display.

Dynamic contrast ratio gives out a higher number and that is the reason you will find this number mentioned in the specification details of most of the TV manufacturers. Unfortunately, Dynamic contrast ratio does not represent the real life TV viewing – it just represents one aspect. As a viewer, you will be able to clearly see that a 20:1 contrast ratio is better than a 10:1 contrast ratio. Now move on this number to 200:1 Vs 100:1, the difference becomes less marked. If you further move on to 200,000:1 Vs 100,000:1, you will probably be not able to make the difference with naked eyes.

The scenario is complicated by the fact that there is no uniform way of measuring the Dynamic contrast ratio. The presence of even slight light will reduce the measured value of the dynamic contrast ratio. Obviously, manufacturers quote the numbers measured in full dark conditions. The matter is further complicated by the fact that the manufacturers may “trick” the TV to give out “extreme black” in “dark condition”, by potentially turning the backlight completely off when measuring the dark level of luminance. Obviously, comparing the dynamic contrast ratio figures between two manufacturers are not meaningful. Possibly, the best use of the Dynamic contrast ratio number is to compare it between two model s of the same manufacturer.

You also need to notice the contrast settings on the television set by default while purchasing it. You can adjust it by accessing the display properties of the television set. Try to adjust manually the contrast value. Compare this with the default factory settings available on the HDTV. Use visual judgment to compare different brands because different brands and different customers have varying tastes on display clarity. The sales people always use the blue ray disc supplied by the manufacturer to demo the product before you. So you need to try another standard DVDs (both high and low quality movies) available in shops to make the final purchase decision. Actually the DVD comes from the manufacturer is maximum adaptable to their TV only. Better performance under poor and moderate input signal is the indication of high quality HDTV product.

You may also like to compare two HDTVs displaying same pictures side by side. Make sure that the display setting is in default condition in both the TVs. Try to judge the quality of the display with visual inspection as a casual viewer. Keep in mind the contrast ratio number, but do not get blinded by these numbers.

Resources :

1. One of the best resources about the Contrast ratio comes from Home Theater Guide. We encourage you to go through this text explaining contrast ratio, its relevance to eye and real life viewing experience.

2. Wikipedia has some decent text about definitions of the Contrast ratio, Dynamic contrast ratio and the effect of room light on contrast ratio number.

This text was written with the intention of helping the readers understand the Contrast Ratio when reading the HDTV reviews.

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