Digital light processing
Digital light processing is a set of chipsets based on optical micro-electro-mechanical technology that uses a digital micromirror device. It was originally developed in 1987 by Larry Hornbeck of Texas Instruments. While the DLP imaging device was invented by Texas Instruments, the first DLP-based projector was introduced by Digital Projection Ltd in 1997. Digital Projection and Texas Instruments were both awarded Emmy Awards in 1998 for the DLP projector technology.
DLP technology is used in DLP front projectors, DLP rear projection television sets, and digital signs. It was also used in about 85% of digital cinema projection as of around 2011, and in additive manufacturing as a light source in some printers to cure resins into solid 3D objects.
DLP was used in a variety of display applications from traditional static displays to interactive displays and also non-traditional embedded applications including medical, security, and industrial uses. Smaller "pico" chipsets were used in mobile devices including cell phone accessories and projection display functions embedded directly into phones.
Digital micromirror device
In DLP projectors, the image is created by microscopically small mirrors laid out in a matrix on a semiconductor chip, known as a digital micromirror device. These mirrors are so small that DMD pixel pitch may be 5.4 μm or less. Each mirror represents one or more pixels in the projected image. The number of mirrors corresponds to the resolution of the projected image. 800×600, 1024×768, 1280×720, and 1920×1080 matrices are some common DMD sizes. These mirrors can be repositioned rapidly to reflect light either through the lens or onto a heat sink.Rapidly toggling the mirror between these two orientations produces grayscales, controlled by the ratio of on-time to off-time.
Color in DLP projection
There are two primary methods by which DLP projection systems create a color image: those used by single-chip DLP projectors, and those used by three-chip projectors. A third method, sequential illumination by three colored light-emitting diodes, is being developed, and is currently used in televisions manufactured by Samsung.Single-chip projectors
In a projector with a single DLP chip, colors are produced either by placing a color wheel between a white lamp and the DLP chip or by using individual light sources to produce the primary colors, LEDs or lasers for example. The color wheel is divided into multiple sectors: the primary additive colors: red, green, and blue, and in many cases white. Newer systems substitute the primary subtractive colors cyan, magenta, and yellow for white. The use of the subtractive colors is part of the newer color performance system called BrilliantColor which processes the additive colors along with the subtractive colors to create a broader spectrum of possible color combinations on the screen.The DLP chip is synchronized with the rotating motion of the color wheel so that the green component is displayed on the DMD when the green section of the color wheel is in front of the lamp. The same is true for the red, blue and other sections. The colors are thus displayed sequentially at a sufficiently high rate that the observer sees a composite "full color" image. In early models, this was one rotation per frame. Now, most systems operate at up to 10× the frame rate.
The black level of a single-chip DLP depends on how unused light is being disposed of. If the unused light is scattered to reflect and dissipate on the rough interior walls of the DMD and lens chamber, this scattered light will be visible as a dim gray on the projection screen, when the image is fully dark. Deeper blacks and higher contrast ratios are possible by directing unused HID light away from the DMD and lens chamber into a separate area for dissipation and shielding the light path from unwanted internal secondary reflections.
Color wheel "rainbow effect"
Single-chip DLP projectors utilizing a mechanical spinning color wheel may exhibit an anomaly known as the "rainbow effect". This is best described as brief flashes of perceived red, blue, and green "shadows" observed most often when the projected content features high contrast areas of moving bright or white objects on a mostly dark or black background. Common examples are the scrolling end credits of many movies, and also animations with moving objects surrounded by a thick black outline. Brief visible separation of the colors can also be apparent when the viewer's gaze is moved quickly across the projected image. Some people perceive these rainbow artifacts frequently, while others may never see them at all.This effect is caused by the way the eye follows a moving object on the projection. When an object on the screen moves, the eye follows the object with a constant motion, but the projector displays each alternating color of the frame at the same location for the duration of the whole frame. So, while the eye is moving, it sees a frame of a specific color. Then, when the next color is displayed, although it gets displayed at the same location overlapping the previous color, the eye has moved toward the object's next frame target. Thus, the eye sees that specific frame color slightly shifted. Then, the third color gets displayed, and the eye sees that frame's color slightly shifted again. This effect is not perceived only for the moving object, but the whole picture. Multi-color LED-based and laser-based single-chip projectors are able to eliminate the spinning wheel and minimize the rainbow effect since the pulse rates of LEDs and lasers are not limited by physical motion. Three-chip DLP projectors function without color wheels, and therefore do not manifest this rainbow artifact."
Three-chip projectors
A three-chip DLP projector uses a prism to split light from the lamp, and each primary color of light is then routed to its own DMD chip, then recombined and routed out through the lens. Three-chip systems are found in higher-end home theater projectors, large venue projectors, and DLP Cinema projection systems found in digital movie theaters.According to DLP.com, the three-chip projectors used in movie theaters can produce 35 trillion colors. The human eye is suggested to be able to detect around 16 million colors, which is theoretically possible with the single chip solution. However, this high color precision does not mean that three-chip DLP projectors are capable of displaying the entire gamut of colors we can distinguish. In comparison, it is the one-chip DLP projectors that have the advantage of allowing any number of primary colors in a sufficiently fast color filter wheel, and so the possibility of improved color gamuts is available.
Light-source
DLP technology is independent of the light-source and as such can be used effectively with a variety of light sources. Historically, the main light source used on DLP display systems has been a replaceable high-pressure xenon arc lamp unit, whereas most pico category DLP projectors use high-power LEDs or lasers as a source of illumination.Since 2021 a laser light source has become very common on many professional projectors, for example the Panasonic PT-RZ990.
Xenon arc lamps
For xenon arc lamps, a constant-current supply is used, which starts with a sufficiently high open-circuit voltage to cause an arc to strike between the electrodes, and once the arc is established, the voltage across the lamp drops to a given value while the current increases to a level required to maintain the arc at optimal brightness. As the lamp ages, its efficiency declines, due to electrode wear, resulting in a reduction in visible light and an increase in the amount of waste heat. The lamp's end of life is typically indicated by an LED on the unit or an onscreen text warning, necessitating replacement of the lamp unit.Continued operation of the lamp past its rated lifespan may result in a further decrease in efficiency, the lightcast may become uneven, and the lamp may eventually become hot enough to the point that the power wires can melt off the lamp terminals. Eventually, the required start-up voltage will also rise to the point where ignition can no longer occur. Secondary protections such as a temperature monitor may shut down the projector, but a thermally overstressed quartz arc tube can also crack or explode. Practically all lamp housings contain heat-resistant barriers to prevent the red-hot quartz fragments from leaving the area.
LED-based DLPs
The first commercially available LED-based DLP HDTV was the Samsung HL-S5679W in 2006, which also eliminated the use of a color wheel. Besides long lifetime eliminating the need for lamp replacement and elimination of the color wheel, other advantages of LED illumination include instant-on operation and improved color, with increased color saturation and improved color gamut to over 140% of the NTSC color gamut. Samsung expanded the LED model line-up in 2007 with products available in 50-, 56- and 61-inch screen sizes. In 2008, the third generation of Samsung LED DLP products were available in 61- and 67-inch screen sizes.Ordinary LED technology does not produce the intensity and high-lumen output characteristics required to replace arc lamps. The special LEDs used in all of the Samsung DLP TVs are PhlatLight LEDs, designed and manufactured by US-based Luminus Devices. A single RGB PhlatLight LED chipset illuminates these projection TVs. The PhlatLight LEDs are also used in a new class of ultra-compact DLP front projector commonly referred to as a "pocket projector" and have been introduced in new models from LG Electronics, Samsung and Casio. Home theater projectors will be the next category of DLP projectors that will use PhlatLight LED technology. At InfoComm in June 2008, Luminus and TI announced their collaboration on using their technology on home theater and business projectors and demonstrated a prototype PhlatLight LED-based DLP home theater front projector. They also announced products will be available in the marketplace later in 2008 from Optoma and other companies to be named later in the year.
Luminus Devices PhlatLight LEDs were also used by Christie Digital in their DLP-based MicroTiles display system. It is a modular system built from small rear projection cubes, which can be stacked and tiled together to form large display canvasses with very small seams. The scale and shape of the display can have any size, only constrained by practical limits.