Display Myths Shattered: Contrast Ratio, Ad Absurdum Part 2/5

Reblogged from MaximumPC
Posted 05/18/10 at 06:03:33 PM
by Dr. Raymond Soneira

Both manufacturers and consumers are obsessed with contrast ratios. Because many people choose the model with the highest number, manufacturers have developed new contrast ratio specs to win at this game.

It’s a sordid business, but deserves exposure, so let’s jump in.

When Contrast Ratio Actually Matters 

A careful, objective measurement of contrast ratio can be very revealing. After the display is accurately calibrated for optimum picture quality, the contrast ratio is determined by dividing the brightness of peak white by the brightness of black. In principle, the greater the ratio the better. Just be aware that contrast ratio is important only for low-ambient-light viewing, which is where black brightness values matter most. (In high-ambient-light settings, reflections off the screen abound, and they’re all brighter than the display’s own internal black.)

Even more to the point, a high contrast ratio really only matters when there is significant dark picture content, like you see in some movies. It’s much less relevant for most TV shows because the picture seldom has much very dark content, and the image never really dips down to black except briefly between scenes. As for games, well, just consider which games really run a lot of “pure” black. If for some reason you’re still playing in the dark, underground worlds of Doom 3, you need a high contrast ratio. But if the colorful world of Plants vs. Zombies is more your speed, you need not worry.

Keeping Up with the Joneses

Contrast-ratio specs are tremendously inflated. For the best LCDs, scientifically measured contrast ratios are actually between 1,500 and 2,000. But manufacturers almost never publish real contrast ratios anymore. You’ll only find these true values in a small number of articles and publications. Yes, contrast-ratio values have been steadily improving over the years, but the year-to-year change is relatively small, which isn’t good for marketing.

Oh, Sony. Even you're playing the absurdly inflated contrast ratio game? A factor of 1,000,000 sure sounds like a lot!

In their quest to quote ever-larger numbers, some manufacturers invented a completely meaningless spec called “dynamic contrast ratio,” which is what’s being prominently advertised now. Sometimes they don’t even bother mentioning the “dynamic” part. Sadly, all manufacturers are now forced to play this game, as consumers wouldn’t be interested in monitors and TVs that tout the true values. Meaningless contrast-ratio specs help substandard manufacturers by making their displays appear to be just as good as those from the best manufacturers, or even better, because the biggest liar wins. This not only hurts consumers, but it also hurts the better manufacturers because they’re unable to publicize their superior technology.

Big but Not Big Enough

So what’s really so “dynamic” about this bastardized contrast-ratio spec? It’s really quite simple: When the display’s video signal is entirely black or very close to black, the display’s electronics go into a standby mode that significantly reduces the light output of the unit. This much darker standby value is then used when computing the contrast ratio—instead of the real value of when a picture is actually present.

Obviously, this trick doesn’t change the true black or true contrast ratio for any picture that’s not all black, so it’s meaningless for picture quality. The primary reason for measuring the spec this way is that published contrast ratios can now go from about 1,500 up to, well, infinity. In 2008, many TVs were advertised with a “dynamic contrast” in the range of 15,000 to 35,000. Now, in 2010, some go into the millions and beyond. There’s no real improvement, of course. It’s just the same trick with a bigger exaggeration.

When Infinite Means Nothing

At my local Walmart in Amherst, New Hampshire, the Sony KDL-52EX700, an LED-based TV, is listed by Walmart as having an “infinite contrast ratio” on its information label. First of all, “dynamic” was left off—it should say “infinite dynamic contrast ratio.” This is then technically correct because the LEDs turn off when an all-black image is present. This results in a division by zero, and produces the infinite result. But this is also nonsense because the LEDs need to be on whenever an actual picture is present!

Labeling like this is intentionally misleading to consumers. Walmart should set an example for other retailers and refuse to show misleading manufacturer specs to its shoppers.

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