Dynamic Contrast Ratio
by DennenTH - 5/6/08 12:22 AM
In Reply to: the more the better. by gabereyes
HDguru.com did have a bit to say on dynamic contrast ratio, so I felt since it was relevant, perhaps I should toss it up here.
"Almost every HDTV manufacturer publishes a contrast ratio number. TV Salesman explains the bigger the ratio, the better. If all other image criteria are equal, the display with the better contrast (brighter whites and darker blacks) would have the best picture and with it the best perceived sharpness. However, this specification has morphed beyond a useful measurement into a new, meaningless number that manufacturers call dynamic contrast ratio. With the recent arrival of 2008 models, it has ushered in the era of dynamic contrast ratio boasting up to one million to one (1,000,000:1). The reality? Not only is the dynamic number meaningless, it reminds me of something Dr. Evil of Austin Powers fame would be promoting.
The way dynamic contrast is measured is a two step process. First the HDTV is fed a completely black signal (0 IRE). The level of black is measured. Next a test signal with a small patch of full white (100 IRE) is generated and the white area is measured. The ratio between the darkest and lightest signal is what is claimed to be dynamic contrast. How does this relate to what you see when watching a TV program or movie? It doesnt! We dont watch content consisting of an all black screen, we see an image that has portions that will be dark (at times) light or something in the middle. An accepted contrast ratio standard measurement is called ANSI contrast, but HDTV manufacturers dont specify ANSI contrast, they just specify contrast so we really dont know how they measure it.
The same display that may provides a dynamic number may spec its normal contrast ratio as 1/30th-1/100th of the dynamic contrast ratio number. Bottom line, disregard the dynamic contrast ratio, it is meaningless.
One last note. Black level is part of the equation, but you cant perceive black level in stores like Best Buy and Costco where the ambient light level is many times higher than a the room in your own home where you view your new HDTV. Unless the dealer has realistic ambient light levels (that match the level of your homes viewing environment), you may not notice that the blacks on the stores demo set are really gray, until you take the HDTV home."
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