The contrast ratio of a TV set, computer monitor or other device screen measures the difference in brightness between the brightest white and darkest black the monitor can display. For example, a 1,000:1 contrast ratio indicates that white areas of the screen are 1,000 times brighter than the black areas. This measurement gives a rough idea of how well a monitor displays blackness and dark scenes, but in some cases, the advertised number has little bearing on reality.
Why Contrast Matters
To visualize the importance of a high contrast ratio, imagine a monitor with a 10:1 contrast ratio. With pure white only displaying 10 times brighter than blackness, the monitor has very few options for the brightness of an image, so every image would appear gray and washed out. Increase the contrast ratio to 100:1, and the range of possibilities opens up slightly. Move up to 1,000:1 and the monitor can properly display a colorful scene with realistic lighting. Keep in mind that if you watch TV or play games in a well-lit room, the ambient light will wash out the screen more than its own contrast shortcomings.
The Grayness of Space
A high contrast ratio allows a monitor to better display pure blacks. Think of an exterior view of the Enterprise on “Star Trek.” Ideally, the space around the ship should have no lighting apart from the stars, but on many LCD TVs, this "blackness" looks like it's been through the wash a few too many times. Because the backlight behind the screen has to remain bright to light the ship properly, blacks turn into grays. Despite other advantages of LCD TVs, this problem wouldn't have happened if you watched the show when it aired in the 1960s: CRT televisions generate light as they draw pixels on the screen, and so do not require a backlight. Similarly, plasma TVs offer contrast ratios superior to LCD TVs by lighting pixels independently.
Watching for Details
Contrast ratio also plays a role in displaying faint details. When a monitor with a poor contrast ratio shows a dark scene, dimly lit objects in the scene tend to blend in to the darkness. This causes problems with some types of TV shows and games more than others: a low contrast ratio has little effect on watching sports, but if you’re playing a game like “Amnesia” or a “Resident Evil” title, poor contrast can cause you to overlook objectives and enemies lurking in the shadows.
Dynamic Contrast Ratio
Some monitors adjust the brightness of the screen depending on the scene or room lighting. This keeps all-black images looking black instead of gray, but it comes at the cost of reducing brightness to the lit areas in dark scenes. Manufacturers advertise dynamic contrast ratios with extremely high numbers, such as 1,000,000:1 or higher, but these ratings have little use in measuring the quality of dark scenes on a monitor: The manufacturer only achieves these dramatic differences by measuring blackness and whiteness on completely different scenes.
- Maximum PC: Display Myths Shattered: How Monitor & HDTV Companies Cook Their Specs
- CNET: Contrast Ratio (or How Every TV Manufacturer Lies to You)
- Crutchfield Labs: LED-LCD vs. Plasma
- CNET: 'One Million' to One: Why Contrast Ratio Is the Dr. Evil of HDTV Specs
- CNET: Should I Upgrade My CRT HDTV? (Morrison's Mailbag)
- Photo Credit -zlaki-/iStock/Getty Images
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