Just as resolution continues to increase on HDTV sets, so it seems does contrast ratio. I few years ago, digital displays were exclaiming how impressive a 1,000:1 contrast ratio was. Now 10,000:1 is not that uncommon. And since contrast ratio is more important to resolution in the production of a great picture, it sounds like these new displays should be amazingly fantastic. Unfortunately, these extremely high contrast ratios have little to do with real world performance and are, to a great extent, marketing hype.
First of all, it’s necessary to understand the difference between the two types of contrast ratio measurements. The one used by pretty much every manufacturer out there is full on (100% white) / full off (100% black). While this can give some amazingly high numbers, people don’t watch all-white or all-black screens. Comparing the brightest whites in one scene to the blackest blacks in another scene is not representative of the picture quality available at the exact instance the viewer is watching each scene. (Measuring the screens at 2 different times also allows further manipulation of the display between tests, such as switching to a different color wheel setting, changing the aperture of an iris, or taking the measurement at a more favorable location on the screen.)
The contrast ratio that matters most for the most common viewing scenarios is ANSI contrast ratio . With ANSI contrast ratio, the black and white levels are measured at the same time on the same screen using a 16-square black and white checkerboard image. What this means is that it is representative of the contrast ratio achievable at any one point in time; this is what is really important to viewers. [Edit: see AlenK's comment below regarding situations where On/Off contrast ratio become important.]
The reason ANSI contrast ratios are not published is because of marketing. ANSI contrast ratios are much lower than on/off contrast ratios. An ANSI contrast ratio of 250:1 would be an impressive result and 600:1 would be outstanding — but much too low of a number if casually compared to an on/off contrast ratio of 6,000:1.
This info is for front projection and does not directly relate to flat panels:
One last point that is critical is the impact ambient light has on perceived contrast ratio. Ambient light kills contrast ratio on any and every display. If you make out the beige carpet below your flat panel, your contrast ratio is being negatively impacted. If there is 1 lux of ambient light in the room (i.e. a small candle), the max perceivable contrast ratio is 500:1. A dimly lighted room with 30 lux of lighting would squash the maximum perceivable contrast ratio to 50:1 . Unless you have a completely dark room covered in black velvet, you’ll never be able to perceive the high on/off contrast ratios claimed by manufacturers — those numbers are meaningless otherwise.
Conclusion: If you’re looking to buy a new HDTV, don’t place much merit on the contrast ratio published by the manufacturer; it is pretty much meaningless for real-world (a little bit of light in the room) viewing. Plus, I’ve never seen a review of a calibrated display meet or exceed the manufacturer published contrast ratios. Look for independent test results that measure both ANSI and On/Off contrast ratio on a properly-calibrated display. If you are always watching TV in a well-lit room, the contrast ratio doesn’t really matter anyway; display brightness is more important the brighter the room is. But if you like to enjoy the full performance of your display by turning the lights off, high contrast ratio is extremely important.
If you’re considering a model for which no reviews listing ANSI and On/Off contrast ratio exist, use this rule of thumb:
- CRT displays are pretty much the king of on/off contrast and give the best black levels, have great color reproduction, but lower ANSI contrast ratios [edited 2007-05-29]
- Plasmas offer almost the same (and often better) on/off contrast ratio performance as compared to CRT and can offer better ANSI contrast ratios.
- DLP is the best for digital front/rear projection displays
- LCoS (aka SXRD, DiLA) are very close to DLP
- LCD (both flat panels and front/rear projection) offers the poorest contrast ratios (especially on/off); however, they can be among the brightest flat panels and that makes them great for bright rooms where it is difficult to perceive contrast ratio.
Like always, there are some exceptions. Always look at a display yourself before you purchase it. LCD flat panels have great bang-for-the buck and look pretty good on a bright show-room floor. See if you can view and compare it in your normal viewing environment (a completely dark room, a very bright room) before you make your final decision. Plasmas have great black levels but are terrible for glare and reflection off the glass front screen; plasma + direct sunlight = unwatchable combination.