What Does "Display Contrast Ratio" Really Mean?

**RedGTiVR6** · 07-25-2006, 05:38 PM

I thought some others might find this interesting:

A high contrast ratio is a desirable feature on any display. By definition, contrast ratio measures the luminosity of the brightest and darkest color that an LCD can display. If a display has a poor contrast ratio there will be a lack of true black and desaturated colors.

There are a variety of methods that can be used to measure a display's contrast ratio and each of these methods can provide a wide array of results for the same display. A typical contrast ratio may be noted as 1000:1 or 100:1. The larger number will result in the best contrast. Display manufacturers and designers prefer different methods of measurements.

Manufacturers measure the contrast ratio based on methods that isolate the display from the system, whereas, designers prefer methods that allow them to factor in the room effect. Ideally a room absorbs all light and the only light displayed would be from the monitor, however, in actual rooms some of the light is reflected back to the display which effectively decreases the contrast ratio.

To further complicate contrast ratio measurements, one must consider both static and dynamic contrast ratios. The static ratio only considers luminosity levels at a single instance in time, whereas, the dynamic ratio considers the luminosity the monitor displays over a period of time. This may be thought of more simply by referring to the static ratio as measuring a static image and the dynamic ratio by considering the affects of a more dynamic or moving image.

Ideal Room Measurement
This type of measurement is typical of manufacturers because it results in the highest possible contrast ratios. This is done by keeping the room at optimum conditions so that the reflective light remains constant. Testing in this manner has no affect on luminance levels, however, it does inflate the light levels.

Real Room Measurement
Contras ratios are more realistic when measured in real rooms that expose the display to conditions where some light is reflected back to the display. ANSI contrast simultaneously measures luminosity values using a checker board patterned test image.

Optimal and Degraded

The Ideal Room Measurement (full on/full off) measurement method effectively measures the dynamic contrast ratio of a display, while the Real Room Measurement (ANSI contrast) is best used to measure static contrast ratio.

Comparing dynamic and static contrast ratios is similar to one trying to compare apples and oranges. These items should never be directly compared. Some manufactures choose to market only the dynamic contrast ratio when the result is better than the display's static ratio. A display with a static contrast ratio of 10000:1 is a much better display than one with a 10000:1 dynamic and 5000:1 static contrast ratio when the input signal contains full range of brightness' from 0 to 100% simultaneously. However the displays will be equal when the input signal range is decreased to a 0 to 20% brightness level.

In order to achieve optimum contrast ratio results, displays are typically measured in completely dark rooms. It will be nearly impossible to achieve these same results during normal viewing conditions. The reduction in contrast ratio will depend on the display luminance and the reflective light in the room.

**senseless228** · 07-25-2006, 06:41 PM

good find, that explains it better than anything i've ever read.

**nameeri** · 07-25-2006, 06:51 PM

Also, just a side note, Transflective screens offer a far superior contrast ratio due to the AR coating and polarizers used as compared to a standard LCD.

**sebberry** · 07-27-2006, 06:06 PM

in layman's terms, the higher the contrast ratio the more levels of color it can display. If you fire up any monitor test app they typically show bands of colors, a gradient from 100% to black. High contrast ratio monitors (CRT for example) won't show any "banding" in that gradient, where low contrast ratio monitors (cheap LCD) will show more. These bands show as steps of colors rather than a smooth transition.

**parksgm** · 07-29-2006, 12:26 PM

Originally Posted by sebberry

in layman's terms, the higher the contrast ratio the more levels of color it can display. If you fire up any monitor test app they typically show bands of colors, a gradient from 100% to black. High contrast ratio monitors (CRT for example) won't show any "banding" in that gradient, where low contrast ratio monitors (cheap LCD) will show more. These bands show as steps of colors rather than a smooth transition.

While it is true that "banding" signifies that a monitor cannot properly display colors that are closely related well, I think your explanation confuses the issue.

The banding you describe could result from a monitor with a perfectly acceptable contrast ratio. An extreme example would be a black and white monitor that displayed pure black and pure white (maximum contrast). A monitor test display pattern would definitely show banding between the two "colors", but it wouldn't because of a lack of contrast. A four, or sixteen color monitor would also show banding if presented with a smooth color or greyscale gradation as a monitor test pattern, but again, this is a seperate issue from contrast.

In my opinion, the banding you describe might result from a color monitor's inability to properly display different color saturation levels on each pixels. I guess that might be consider an inability to properly "contrast" between the colors, but I think in normal usage when discussing monitors, contast implies the contrast ratio betwen the lightest and darkest possible pixels that can be displayed.

Largely a sematic difference to be sure, but just my two cents, anyway. :-)