Everyday thousands of people visit the Digital Forum looking for information about High definition television (HDTV) and every day we try and help our readers out by answering their frequently asked questions.

In this HDTV FAQ article we answer the question – Is Dynamic Contrast Ratio meaningful?

In the consumer electronics industry, bigger numbers sell more products. Why would a consumer buy an HDTV with a dynamic contrast ratio of 20,000:1 when they could buy one with a 30:000:1 ratio for the same price?

The truth is those dynamic contrast ratio numbers you are reading on manufacturers website are meaningless and should never be used when buying a high definition television.

What is Contrast Ratio?

The contrast ratio is a measure of a display system, defined as the ratio of the luminosity of the brightest color (White) to that of the darkest color (black) that the system is capable of producing.
These measures are both expressed in candelas. For example, a monitor with a white at 250 cd/m², and a black at 0.50 cd/m² has a contrast ratio of 250 / 0.50 = 500:1.

A high contrast ratio is a desired aspect of any display, but with the various methods of measurement for a system or its part, remarkably different measured values can sometimes produce similar results.

Their are two methods for measuring contrast ratios: Full On/Off, ANSI and dynamic contrast.

Full On/Off contrast measures the ratio of the light output of an all white image (full on) and the light output of an all black (full off) image. If given a choice, manufacturers favor the use of the full on/full off method of measurement because it yields a much higher contrast ratio than ANSI contrast measurements.

ANSI contrast is measured with a pattern of 16 alternating black and white rectangles in a checkerboard pattern and the luminosity of each rectangle is measured. The average light output from the white areas is divided by the average light output of the black areas to determine the ANSI contrast ratio. This method is generally believed to be a more realistic measure of contrast ratio.

In the marketing literature today, there is typically a third contrast ratio quoted, Dynamic. If the type of contrast ratio is not stated as Full On/Off or ANSI then assume dynamic. The truth is there is no benchmark for measuring dynamic contrast ratios and manufacturers have typically claimed dynamic contrast ratios that bear little or no relation to ANSI contrast ratios.

For example, last year one LCD manufacturer reported a dynamic contrast ratio of 1,000,000:1. Subsequent testing by an independent firm, found its ANSI contrast ratio was just over 3,000:1.

The moral of the story is that if you are hoping to compare display devices by comparing contrast ratios, then you are wasting your time. There is no one method used by manufactures to measure the contrast ratios of their monitors and HDTVs and manufacturers seldom, if ever, report what method was used to calculate contrast ratio.

This lack of standards in measuring contrast ratios makes it impossible for a consumer to make a straightforward comparison of contrast figures between different HDTV’s impossible.

Discuss in Digital Home's High Definition Television (HDTV) forum.