Simply put, Dolby local dimming technology has greatly improved the visual effect of LCD screens. Compared to HDTV monitors, these technologies stand out quickly, demonstrating surprisingly realistic images, which have almost all the contrast in nature, colorful colors, pure black, and dark lines with only slight differences. Such an inviting visual experience is undoubtedly superior to traditional monitors.
Using local LED backlight instead of the current traditional cold cathode fluorescent tube (CCFL), Dolby High Dynamic Range technology specifically addresses the limitations of LCD displays through a unique design. Our technology enables the image to reach the full visual dynamic range that can be seen by the naked eye. It is achieved by controlling the local brightness in order to provide the precise level required by each small block in the image.
LCD panel performance advantages and disadvantages
Basically, an LCD screen is composed of an LCD array plus various shielding and diffusion arrays and a backlight module. The LCD itself does not emit light, and depends on the brightness of the backlight to generate an image on the screen.
The advantage of the current LCD technology is the resolution, but there are also shortcomings, so that it can not restore a completely realistic image. Even in its closed state, the LCD cannot completely cut off the bright light from the CCFL, and some faint light always escapes. Therefore, LCD flat panel displays cannot be true black, and are limited to a contrast ratio of 1200: 1. The black level can be improved by lowering the backlight, but at the expense of brightness. Even when the image only needs a very small brightness, the brightness and power consumption (of the LED) remain constant.
Although high-definition images are more prominent than standard-definition images, the inherent characteristics of the backlight make some colors, especially skin tone, color depth, and texture look less realistic.
Alternative to LED-CCFL backlight
CCFL backlight prices are relatively low, and the process has been improving. Due to the defects of CCFL, the display industry is beginning to shift to an alternative process, namely LED technology. This new technology has begun to be applied to the LCD screens of a large number of small laptop computers, and a manufacturer has established an LED-backlit TV production line.
LED has inherent advantages. It is environmentally friendly because it does not contain mercury and has a long life. Its response time is shorter than CCFL, and RGB LED can be used to increase the chromaticity range. According to the amount of light emitted per unit power consumption, the energy efficiency of LEDs has increased exponentially. From an economic point of view, the cost of LEDs (US dollars per lumen per watt) is falling rapidly, in fact, faster than the cost of CCFL.
The main point of the current trend is that not only is the backlight of the display, but also some other requirements jointly promoted, LED process improvement and cost reduction will continue. More industries are exploring applications that are beneficial to LEDs, for example, in the headlights and taillights of high-end cars.
Figure 1: Traditional display processing architecture
Restore realistic dynamic range
From the brightest to no light at all, the difference between light and dark, the dynamic range that the human eye can perceive is 14 orders of magnitude (logarithm).
At the moment of entering the visual environment, the dynamic range that the eye can perceive is about 5 orders of magnitude, and it will gradually adapt to it. The display of the traditional craft still in use today can only restore 3 orders of magnitude, which is the main factor that the image on the screen looks unrealistic. Nowadays, LCD technology can match the human eye's perception ability in most fields, such as sharpness and motion capture (refresh rate of displayed image), but it still can't get close to our eyes in brightness range.
The Dolby Contrast process greatly improves the dynamic range by simultaneously increasing transient contrast and black level fineness. Dolby Video Technology restores the dynamic range of brightness that can be recognized by the naked eye at the same instant, and also greatly enhances the dynamic contrast, while providing excellent black level fineness. Dolby Vision technology even further makes the image so real that the image becomes a window in the real world.
Figure 2: Comparison table of LCD performance
Advantages of Dolby local dimming technology
Dolby local dimming technology provides many obvious benefits, for a variety of reasons, the use of Dolby contrast and Dolby Vision displays can achieve unexpected outstanding results.
Dolby local dimming technology can produce pure black by turning off the black local backlight in the image.
Using Dolby technology can produce bright white. The image that appears in our eyes is the exact reproduction of the reflected light of an object (just as sunlight is reflected by water). The traditional LCD cannot do this because its backlight brightness is not enough. Dolby contrast and Dolby Vision technology can selectively brighten the bright local backlight in the image, making the emitted light more realistic.
Dolby Vision technology greatly improves the dynamic range of chroma and brings vivid colors. The extra red is red, followed by bright blue, pure black and all colors in between. It has made minor improvements in quite a few places to improve the image quality.
Dolby Vision technology improves the characterizable chromaticity fineness by several orders of magnitude, approaching the range of color depth in real life. For example, it accurately restores the delicate skin tone. Because the human eye uses the depth of color to assist the perception of the stereo vision range with a depth of more than about one meter, Dolby Vision images have 3-dimensional quality, including additional color depth and fineness, which are discarded in traditional displays.
In addition to the fascinating image quality, Dolby local dimming technology can also reduce considerable power consumption, depending on the content of the image.
Figure 3: Dolby visual experience solution block diagram
Using LED backlight to solve the limitation of LCD
Traditional LED backlight has not been used to solve the limitations of LCD performance. In current mainstream applications, LED backlights with constant brightness have failed to improve contrast and black gray levels. A relatively compromised improvement method is unified dimming, commonly known as OD dimming or backlight modulation. In this method, the entire backlight is darkened to present a basic black and brightened to highlight the bright scene. In any case, because the brightness of most images is relatively average, this approach can only provide limited improvements in improving the quality of the image.
Dolby has developed a breakthrough technology that can lower the backlight brightness to a new level. Dolby ’s patented development covers all implementations of local dimming, so-called 1D and 2D dimming. Through these, the backlight is divided into a series of areas. These areas are dimmed or brightened independently according to the brightness requirements of the corresponding areas in the image. The finer the number of independent local areas, the better the overall contrast.
Many new display technologies also use some degree of local dimming technology, but they still cannot achieve the performance of Dolby technology. In particular, it cannot match the additional benefits of Dolby Vision imaging technology.
Dolby Contrast and Dolby Vision complete solutions
The patented Dolby Contrast technology focuses on solving the limitations of the current LCD, and replaces the unified backlight control with the local backlight control. This can adjust a single LED, or several LEDs, considerably enhancing the static and dynamic contrast.
Dolby Contrast Technology utilizes LED backlights that are optimized for location. Dolby technology first analyzes a standard 8-bit video frame to match the higher contrast levels that can be achieved with local brightness backlight control. Then analyze each video image frame and calculate the backlight driving level of each LED. For each frame, each image is generated by multiple LEDs, as well as the influence of the adjacent LEDs and the optical characteristics of the display.
Dolby Video Technology has added advanced high dynamic range processing technology. Expanding 8-bit video frames to 16-bit frames realizes dynamic compensation of image grayscale. In addition to some other Dolby contrast processing, Dolby Video Technology also implements LCD image generation compensation based on LED backlight and some display parameters.
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