What Is Dynamic Contrast Ratio?

Dynamic contrast refers to the contrast value measured by the liquid crystal display under certain specific conditions, such as testing each area of the screen one by one, and using the contrast value of the area with the highest contrast as the contrast parameter of the product. Different manufacturers may have different measurement methods for dynamic contrast, but their essence is also inseparable. Dynamic contrast and true contrast are two different concepts. Generally, the dynamic contrast of the same LCD monitor is 3-5 times the actual contrast. Therefore, the dynamic contrast is just a digital game played by the manufacturer, and has no practical meaning.

Dynamic contrast

Dynamic contrast refers to

At present, the contrast ratio of mainstream LCD monitors is mostly at the level of 50,000: 1 to 70,000: 1. Some first-tier brands, such as Asus, Samsung, LG and other manufacturers, have a contrast ratio of 80,000: 1 or even 100,000: 1. The Canadian company Brightside's DR-37P ultra-high dynamic range liquid crystal display with LED backlight technology claims to have an ultra-high contrast of 200,000: 1, which is really a bit startling.

On September 22, 2009, ViewSonic launched the world's first 10 million: 1 dynamic contrast LCD monitor-VX1932wm. Since then, the dynamic contrast upgrade war has begun. So far, Acer has launched a 100 million: 1 dynamic contrast display.

Dynamic contrast

In simple terms, the dynamic contrast is the same as the full on / full off contrast, and it is also the ratio of the brightness displayed by the monitor when it receives an all-white signal to the brightness of the all-black signal monitor. Different from full on / full off contrast, the display will adjust the brightness of the backlight tube to make the display brighter when receiving an all white signal, and the brightness of the display receiving an all black signal will be lower. Value.

For example, for a display with a full white screen brightness of 200cd / m2, if the brightness of a full black screen is 0.1cd / m2, its dynamic contrast is 2000: 1; if the brightness of a full black screen is reduced to 0.01cd / m2 m2, its dynamic contrast has reached 20000: 1; if the manufacturer completely turns off the backlight for a completely black screen in the control circuit, the brightness is 0cd / m2, and the dynamic contrast will be "infinity"! For example, the recently released MS series LED liquid crystal display from ASUS refreshed the dynamic contrast of the panel to a height of 10 million to 1. Moreover, according to Asus's technical engineers, 10 million to 1 will become the new standard for dynamic contrast ratio of LED liquid crystal displays.

Through the analysis above, we can find that the dynamic contrast is mainly to ensure the brightness of bright scenes and to be dark enough in dim scenes. Therefore, the dynamic contrast has obvious practical significance for those applications that frequently switch between bright and dim scenes. For computer applications, the text processing, Internet access, office, and programming all basically have no significant changes in light and shade; most of the game brightness is within a fixed range, although it can not be said that the bright and dim screen switch , But rarely. Taken together, only video is the need to frequently switch between light and dark scenes in computer applications, so only video is the application with the highest dynamic contrast.

Dynamic contrast grayscale is the key

Since dynamic contrast is a bit unreliable, which index should we use when buying LCD TVs / monitors?

Look at grayscale! In practical applications, we should look at the performance of the display from two aspects: contrast and grayscale.

Grayscale refers to the difference between the light and dark of the display pixels, which appears as a difference in color in a color display. The more grayscale levels, the clearer and more vivid the image level. The gray level depends on the number of refresh memory cells corresponding to each pixel and the performance of the display itself. If the color of each pixel is represented by a 16-bit binary number, we call it a 16-bit image, which can express the 16th power of 2 or 65536 colors. If each pixel is represented by a 24-bit binary number, we call it a 24-bit image. It can express 24 to the power of 2, which is 16,777,216 colors. The higher the number of bits, the richer the transition between light and dark. The details are even better.

It should be noted that grayscale performance and contrast are linked. Without a good contrast as the basis, grayscale performance will not go there. Liquid crystal displays have structural defects in the number of color digits, that is, grayscale expression. Although theoretically it can reach 24-bit color displays, in practice, according to different products produced by different manufacturers, many of them fail to meet this requirement. As a result, the complaint above appeared-the black part was not gray enough to express the details. Even if the same core panel is used, the products produced by different manufacturers are not the same.

A typical gray bar, the last 3 divisions are more difficult to observe, even on displays with high contrast

Please pay attention to the details of the hair. Only when the contrast and grayscale are well matched can the details be enriched, and the picture is not exposed.

A really good product should be a good combination of high contrast and excellent grayscale transition. Such a product has bright and vivid colors, and the details are in place without exaggeration.

Dynamic contrast dynamic backlight system

The introduction of dynamic contrast is actually to make up for the shortcomings in the liquid crystal display mechanism, because both CRT and plasma have the ability to display local peak brightness, DLP devices also have high real contrast, and if the LCD has to achieve the same peak brightness, it has to Increase the brightness of the backlight so that it performs better when displaying bright scenes.

However, after increasing the backlight brightness, it cannot be guaranteed to be sufficiently black in black scenes. Dynamic backlight control solves this problem very well. When the black scene is turned down, the backlight brightness is appropriately reduced to make the black scene sufficiently black. However, it still cannot resolve the contradiction between the dark area and the highlight area on the same screen. It cannot fully take care of the bright lights at night and the shadows in the sun.

Therefore, the introduction of the dynamic backlight system and the identification of the dynamic contrast are indeed helpful to the improvement of the display effect of the liquid crystal display. However, there is always a degree to everything. Too dark things cannot be seen by the human eye. If you simply increase the number of dynamic contrast and greatly reduce the brightness in dark scenes, it is easy to cause the screen to be black and unrecognizable to the human eye.

According to the author's personal experience, when the dynamic backlight system reduces the brightness of a dark scene, it is still acceptable to reduce it to 1/2 to 1/3 of the original scene brightness. Beyond this limit, too low brightness can easily cause the dark scene to become black, and the details are all unclear.

In addition, the adjustment design of the dynamic backlight system is also very important. Some manufacturers do a good job and will design it: after a few seconds into the dark scene, gradually reduce the brightness of the backlight system, so that there is a transition process in the middle. Some of the poorer manufacturers will design the backlight system to reduce the brightness as soon as it enters a dark scene. Once certain movie scenes need to switch back and forth between light and dark environments, users will find that the screen flickers. Or when some movie scenes are switched just when the system design cuts the threshold of brightness reduction, the screen may appear flickering.