Home Theater Projector Buyer's Guide: Contrast

Contrast is the difference in brightness between maximum white and deepest black in an image. The greater the difference, the higher the contrast.

Why is Contrast so important?

With business projectors, lumen output is of primary importance, and contrast is a secondary concern. Home theater projectors are the exact opposite. Contrast is arguably the single most important measurable quality in a home theater projector. A high contrast projector produces a picture with a rich, dynamic look, good shadow definition, and deep color saturation. Contrast gives "depth" to video images. A projector with excellent contrast can make a two-dimensional image appear almost three-dimensional.

Contrast Ratios

The contrast ratios noted on a projector's spec sheet can be reported in one of two ways. If it just says "Contrast," it usually indicates On/Off contrast, which is the ratio of the whitest white and the darkest black that the projector is capable of producing. If it says "ANSI contrast," the ratio has been determined by displaying a checkerboard pattern of white and black squares and measuring the relative brightness of each. On/Off contrast is always a larger number, and more typically listed on projector spec sheets, but ANSI contrast is a more accurate representation of what your projector is actually capable of during normal use.

Typical Contrast Specifications

Some typical On/Off contrast figures for home theater projectors are as follows:

• 2000:1

  There are many entry-level projectors rated at 2000:1 on/off contrast. 2000:1 is typically enough to give satisfying black levels and color saturation, enough to avoid the sense of flatness or muddiness in a picture.

• 5000:1

  Projectors rated at 5000:1 are usually capable of better blacks than 2000:1 projectors, and shadow details are better defined. In today's market, 5000:1 represent the midrange of performance for good home theater projectors.

• 10000:1

  As of this writing, if you want the best contrast that money can buy, you want a projector rated at 10000:1 contrast or higher. These projectors offer deep, inky black levels and excellent shadow detail that should be sufficient for even the most demanding content.

What about a dynamic iris?

A dynamic iris is a device built into some projectors that sits between the lamp and the lens. Many times per second, the projector evaluates the overall brightness of the image being projected at the moment, and then opens or closes the iris to allow more or less light through.

A good dynamic iris will improve on/off contrast. Dark scenes will appear darker, while bright scenes will appear brighter. The contrast ratings will be based on the whitest white with the iris opened, and the blackest black when the iris is closed. That means that the projector will never achieve the rated contrast in any given scene. From a practical perspective, a projector that has no dynamic iris and is rated at 3000:1 contrast may actually appear higher in contrast to the eye than a projector rated at "up to 10,000:1," but with that rating based on its dynamic iris variations.

So once again, as with the ANSI lumen ratings, it is best to take official contrast specifications with a grain of salt. They can be highly misleading.

Dark Room Needed for Best Results

You've noticed that commercial movie theaters are dark, including dark ceilings and walls. That is because any front projection system looks its best when there is no light in the room. Once you introduce ambient light into the room, that light will hit the screen and make blacks look more like dark gray. This reduces the contrast of the image, and makes it look flat or washed out. And this will happen no matter what the contrast capability of your projector is.

Though the ideal viewing room is dark, most people don't want to darken the walls and ceiling of a living room or multipurpose room just to get ideal theater conditions. Today's high contrast gray screens help to hold black levels solid when there is some ambient or reflected light bouncing from light colored surfaces in the room back onto the screen. But for the best possible image quality for any home theater, take whatever steps you can to eliminate ambient light and reduce the reflectivity of the room's walls and ceiling.