What is Dynamic Contrast Ratio?

Television, or what most parents and teachers describe as the 'Idiot Box', has undergone a quantum leap since its invention. Some of us who have witnessed black and white TVs sans remote, will vaguely remember fidgeting with the contrast, brightness, and sharpness knobs of the television.

The gray images on the screen were adjusted according to what your eyes perceived as a balanced contrast ratio.

Contrast ratio is the ratio of luminance of the brightest color, that is, white, to that of the darkest color, that is, black, a system can produce. This measurement of the brightest color to that of the darkest color is seen on computer monitors, cathode ray televisions, LCD televisions, and other similar electronic displays.

In an all white screen compared to an all black screen, a full on/full off approach of measurement of static or dynamic contrast ratio is used. This method cancels out the effect of the room and gives the ideal ratio.

As long as the room effects remain the same, equal light proportions are reflected from the display in black' and 'white' measurements to the room and back. This causes the black to white luminance ratio to remain unaffected as the light levels of both the measurements inflate proportionally.

The other methods of measurement include a clear sector of the color filter wheel for the 'on' part and disabling it for the 'off' part. Another method is use of the ANSI contrast, where a checkerboard pattern test image luminosity is measured simultaneously.

In case of dynamic contrast ratio, the most effective method of measurement is the full on/ full off method. Static contrast ratio is measured by the ANSI contrast method.

The number of the brightest white in a bright scene or image is taken and compared to the darkest black in a low-lit scene. When a dark image is displayed, the backlight is underpowered by the display which proportionately amplifies the transmission through the LCD panel.

So if the image is watched in a dark room, the potential static contrast ratio of the LCD panel in dark scenes is benefited. The emitted luminous intensity or brightness is measured in candela per square meter (cd/m²). Thus, higher the number, the screen will appear even brighter.

When considering the best dynamic contrast ratio, you need to consider the human eye first and foremost. The human eye can resolve a contrast ratio of 1000:1 at any point of time. The human eye can also change its sensitivity to light with time.

For example, if you happen to enter a dark room directly from sunlight, the eyes will take about half an hour to adjust. The overall contrast ratio it can resolve is 1,000,000:1 over this time. So, a good dynamic contrast ratio should be anything over 1500:1. The best for LCD TV will be above 10,000:1.