#Screen-Dooreffect

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LCoS projectors

The rapid development of innovations based on digital technology is the main trend for all segments of consumer electronics. Of course, high-tech projectors are no exception. For several decades, the projector has become a complex digital device with huge media capabilities. The projector in the smartphone, miniature Pico and Cube projectors with semiconductor light sources (LEDs or laser LEDs) perfectly illustrate this trend. As known, modern models form a projection image using DLP, 3LCD or LCoS technology. DLP and LCoS technologies use reflected light, while LCD works on the light pass. Of course, each of them has its pros and cons, but they all have been successfully competing in the market for many years.

LCoS (Liquid Crystal on Silicon) operation principle

LCoS can be positioned as a hybrid of 3LCD and DLP technologies. In fact, the LCoS matrix is an LCD matrix that is glued to the mirror. The control semiconductor layer on the substrate with a reflective surface is under the matrix with an array of liquid crystals, protective glass and a polarizer. The spatial orientation of the liquid crystal in the semiconductor layer depends on the control signal.

In fact, it adjusts the transparency of the cell, ensuring control of the light flux passing to the reflective layer and back.

Thus, the liquid crystal matrix modulates the luminous flux, using not the light pass, but its reflection. The light from the source is divided by a system of dichroic and simple mirrors into three light streams corresponding to red, green and blue. Further, each of them falls on its own Polarizing Beam Splitter (PBS) and on the reflecting matrix. The matrix modulates the light, forming the color components for each color channel. They pass back through the PBS and come together in a dichroic prism, forming a color image. The resulting picture is projected through the lens on the screen.

Today several companies use this principle of image formation, having patented their own developments. The list of the most popular includes SXRD (Silicon X-tal Reflective Display) from Sony, D-ILA (Direct Drive Image Light Amplifier) from JVC.

PROS & CONS

The developers of LCoS technology initially set themselves the task of combining the advantages of 3LCD and DLP technologies, of course, without their cons. LCoS projectors provide very high image quality, high brightness and contrast. Moreover, they support the projection with very large image format. In addition, the production technology of reflective matrices allows companies to place the control conductors and electronics behind the reflective layer, increasing the coverage area of the pixels. As a result, these models do not have a screen-door effect.

In addition, LCoS technology allows companies to create matrices with a very high resolution, which certainly corresponds to the modern trend. Of course, these projectors use many other innovative solutions. For example, JVC projectors control an array of points with analog signals, providing smoother color gradients. PROS - a high coefficient of useful filling the matrix surface (the distance between adjacent elements is only a few tens of micrometers) reduces the Screen-door effect and increases the resolution; - LCoS chip is more resistant to high temperature due to placement on the cooling substrate. As a result, powerful installation projectors use mainly LcoS technology; - deeper black and high contrast compared to 3LCD; - fast response time; - lack of flicker and rainbow effect. CONS - high price; - great weight; - large weight and size; - high fan noise for cooling a powerful lamp; - limited lamp life requires additional costs for its replacement. Of course, these features significantly influence the choice of the optimal projector. Today BenQ, JVC, Viewsonic, Canon, Aser, Epson, Sony, LG, Barco, CrystalView, DreamVision lead in this segment. This video demonstrates the Sony SXRD (LCoS technology) VPL-VW870ES, VW570ES and VW270ES projectors. Read the full article

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DLP vs LCD vs LCoS projectors

As known, the whole history of the consumer electronics development is accompanied by fierce competition. It forces companies to constantly increase competitiveness, expanding the functionality of their models and reducing its costs. Of course, the solution of this problem requires the active use of innovative technologies. As a result, companies are investing heavily in their development. As a consequence, today the market often offers similar in consumer qualities models using different technologies. LED LCD, OLED (LG), QLED(Samsung) and NanoCell (LG), Micro LED models in a TV segment perfectly illustrate this trend. High-tech projectors are no exception. Today, models with DLP, 3LCD, and LCoS (D-ILA, SXRD) projection technologies successfully compete in the market. In addition, the development of the segment with LEDs and laser LEDs as light sources initiated the rapid development of portable models of various form factors (pico, cubed, micro, pocket). Moreover, advances in precision technology for manufacturing aspherical lenses and reflective mirrors pushed the development of very popular Ultra Short Throw (UST) projectors, which are able to create huge high-quality projections at a distance of several tens of inches. LG PF1000UW perfectly demonstrates these possibilities. Of course, this situation provides a very rapid improvement of household appliances that pleases consumers. Unfortunately, this wonderful trend has a side effect. Today, the conscious choice of the optimal device requires some effort from the consumer. Of course, the price and functionality remain the main criteria. The price depends entirely on company policy and we cannot influence it. But assessing the price / quality ratio is sometimes a difficult task because of the abundance of offers, which often contain a marketing component. Therefore, even a simplified classification can partially simplify this task.

Operation principle

As known, DLP (Digital Light Processing) uses a semiconductor DMD (Digital Micromirror Device) chip from Texas Instrument with an array of micromirrors to reflect light. In fact, each micromirror corresponds to one pixel. The control signal tilts the micromirror at an angle of ± 12 °, forming a white or black dot on the screen. The frequency of control signals in modern models reaches several kHz. Today, the company produces a wide range of DMD, including, for example, DLP 2000 (0.20 "), DLP 2010 (0.21"), DLP 230GP (0.23"), DLP 230KP (0.23"), DLP 230NP ( 0.23"), DLP 3010 (0.31"), DLP 3310 (0.33") and DLP 4710 (0.47"). They support display resolution from 640 x 360 (nHD) to 1920 x 1080 (1080 p or Full HD). But DLP projectors form a color image on the screen, alternating a sequence of projections with different colors and creating the illusion of a color image due to the high frame rate. The color wheel with segments of different colors serves as a color filter. As known, 3LCD technology was developed by Epson. It uses the influence of electricity on the spatial orientation of liquid crystal molecules. In fact, its matrixes work in the same way as traditional LCD matrices in TVs. But unlike the DLP projector, the 3LCD models form a color image with the help of special prism from three mono-color images. The LCoS (Liquid Crystal on Silicon) projectors combine the best qualities of DLP and 3LCD technologies. Today, its versions of SXRD (Silicon X-tal Reflective Display) from Sony and D-ILA (Direct Drive Image Light Amplifier) from JVC are the most popular.

Contrast ratio

Of course, the image quality dependents on the contrast. As known, this value characterizes the ratio of the brightness of the brightest and darkest pixels. Specs of projectors or TVs contain it in the form of, for example, 60,000: 1. Accordingly, the contrast depends on the maximum brightness and depth of black. In fact, contrast provides depth and dimension of the image, which affect the realism of perception. Today DLP technology in the DLP and LCoS projectors provides higher contrast compared to LCD models. The use of reflection allows engineers to achieve very deep black due to the complete cut-off of light. LCD matrixes use the light pass and cannot ensure its complete blocking. But on the other hand, powerful lamp 3LCD projectors partially compensate for this factor with higher brightness. Many models use effective Auto Iris technology, which adjusts the aperture depending on the illumination of the scene in the frame.

Brightness and color

The brightness characterizes the light intensity in ANSI lm or lm. It has several names, including the light output or lumens rating. This value mainly depends on the type of the light source in the projector. Today, lamps and lasers provide maximum brightness. But the lamps are quite expensive and have a limited service life (4,000-6,000 hours). Laser LEDs provide high power and long service life, but are expensive (mainly due to expensive green lasers). LEDs have a very long service life (20,000-30,000 hours) and are relatively inexpensive, but do not provide sufficient brightness. In turn, brightness affects viewing comfort. Low brightness requires dimming the room to produce acceptable image quality. High brightness provides it even in daylight. Unfortunately, powerful lamps get very hot during operation and require efficient cooling. In turn, the noise during the operation of powerful fan reduces the viewing comfort. Therefore, the choice of brightness represents a trade-off between durability, dimming requirements and noise level. The type of light source mainly depends on the positioning model (portable, home theater, etc) and does not depend on technology. But in general, the 3LCD models often use lamps, and DLP and LCoS - semiconductor light sources (LEDs or laser LEDs). Color accuracy, color range and saturation depend only on the model class.

Motion Blur and Input Lag

As known, this effect is visualized in highly dynamic scenes. Companies solve this problem by increasing the frequency or using the interpolation method that TV manufacturers have been using for years. This technology is based on the formation of intermediate frames by the processor. Today, almost all leading companies use this technology and own indexes for TVs, including Motion Clarity Index (MCI), Clear motion rate (CMR), Picture Quality Index (PQI), Perfect Motion Rate (PMR), Motionflow XR, etc. Unfortunately, increasing the processor load significantly increases Input Lag. Therefore, some projectors automatically disable it in game mode. As known, Input Lag is especially important in games. This value in many modern projectors does not exceed several tens of milliseconds. But some projectors provide an unprecedented low Input Lag, which allows them to be positioned as game models. For example, the Input Lag of UST ViewSonic PX800HD does not exceed 16 ms with 3X Fast Input option. With other things being equal, DLP projectors are confidently leading in this aspect compared to 3LCD and LCoS models.

Rainbow and Screen Door Effects, and Dust Resistance

Rainbow effect appears as multicolored points along the contour of contrasting objects in the frame. It's caused by using a color wheel and shown only in 1-chip DLP projectors. Increasing the speed of its rotation reduces the effect. However, today companies successfully solve this problem in various ways, including, for example, using the innovative RGBRGB color wheel. Of course, LCD and LCoS projectors do not have this effect due to the lack of a color wheel. Screen Door Effect is a visualization of pixels on the screen at a short distance. The high pixel fill factorI duu to the minimum distance between micro mirrors in the DMD chip almost completely eliminates this effect in DLP projectors. Unfortunately, 3LCD models, especially inexpensive, form an image with this effect due to the rather large distance between the matrix crystals. However, more expensive models successfully compensate for it by high resolution. LCoS projectors form an image without this effect. Of course, dust significantly reduces the quality of optics, which is one of the main components of any projector. From this point of view, DLP projectors have a great advantage, because DMD chips are superbly sealed. 3LCD and LCoS models use sealed or non-sealed chips. More expensive models have additional protection.

Conclusion

1. DLP projectors have minimum dimensions and weight. As a result, this technology dominates among portable models. LCoS projectors are the most heavy and large. 2) DLP models provide excellent deep black, but only medium contrast due to the relatively low brightness. LCoS provides better contrast. 3) Low-cost 3LCD models require periodic cleaning of LCD matrices due to insufficient dust resistance. 4)The pixels on the matrices of 3LCD models can burn out over time. 5) With the same specs, today LCoS models are the most expensive, and DLP projectors have a minimal price. Of course, all these factors affect the choice of the optimal projector. This video offers the review of all technologies in modern projectors, including DLP vs 3LCD vs LCoS. Read the full article

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What is projector and its types?

The development of digital technologies for several decades provokes the rapid development of almost all segments of consumer electronics. Today, even a relatively simple household appliances is a complex multi-functional device. Smart coffee machines, robotic vacuum cleaners, washing machines, etc with Wifi support and complex algorithms for auto modes perfectly illustrate this trend. Of course, high-tech projectors are no exception. Modern projectors have evolved from simple devices to project an image into sophisticated digital equipment with huge media capabilities. The projector in the smartphone, miniature Pico and Cube projectors, 4K HDR models, etc perfectly illustrate this trend. Modern technologies have successfully solved the problems of their image quality, compactness, brightness, durability, noise and cost. Today, the market already offers 4K HDR models with a price range of $ 1,000 - 1,500. As a result, many consumers increasingly perceive the projector as an alternative to TV, increasing demand in this segment. Of course, companies are adequately responding to the market conditions by expanding their model lines. But the abundance of proposals sometimes complicates the choice of the optimal model. Therefore, even a simplified classification can help solve this problem.

The number of matrices

As known, the projector matrix provides filtering the luminous flux, passing or blocking it. Therefore, the matrix can form only a single-color image. This is fundamentally different from the matrix of the TV or monitor, which forms a color image. Three-color matrixes are not used in projectors for several reasons. First, almost all the first projectors used high-power bulbs with high heat dissipation for illumination. Therefore, the LCD matrix requires very powerful cooling, which affects the noise, size and cost. Secondly, the three-color matrix does not provide an ideal square pixel. A single-color matrix forms a color image, combining three separate images. 3-chip projectors combine the images and display the finished color picture. Single-matrix models alternately project mono-color images onto the screen, creating the illusion of a color image due to the high frame rate. PROS and CONS 1. 1-chip projector is more compact, but uses more complicated and more expensive matrix. 2. 1-chip projector provides lower brightness due to less efficient use of the bulb luminous flux. 3. Playback in 1-chip models is often accompanied by the rainbow effect due to the non-synchronous speed of changing the image color components. 4. A 1-chip projector provides a perfectly accurate pixel shape, which depends only on the projector optics. The accuracy of the borders of the individual pixels in the 3-chip projector depends on the accuracy of manufacturing and placement of the matrixes. This problem sometimes occurs in budget 3-chip models from lesser-known manufacturers.

Light source and sizes

Modern models use UHP (mercury) or powerful xenon lamps or semiconductor light sources (LEDs, LED lasers). Often, vendors use the name of a laser projector for models with LED lasers as a light source. Of course, this is not entirely correct. Developed in 1991, LDT (Laser Display Technology) technology really uses lasers to form images. The working prototype of the LDT projector was introduced in 1997, and the serial prototype in 1999. Today, these models belong to the professional segment of very expensive installation projectors. Laser in the name of DLP and LCoS models only indicates the use of LED lasers as a light source. Of course, the use of only one chip provides the advantage of DLP technology in terms of compactness. Combined with the LED light source, it provides the production of portable projectors. Their enormous popularity even provoked the formation of a separate segment of compact projectors (mini, pocket, cube, pico).

Projection image formation technologies

Modern projectors form a projection image using DLP, LCD or LCoS technology. DLP and LCoS with DMD chip use the reflected luminous flux, and the LCD works on the light pass. Of course, each of them has its own features, pros and cons, but all of them have been successfully competing in the market for many years. PROS and CONS of DLP and 3LCD projectors Some 3LCD models can have Screen-Door effect (SDE) The control elements of DLP matrices are located under the mirrors, but in the 3LCD matrices they occupy some space around the pixel, forming a small gap between them. As a result, the image on the screen can display the edging of each pixel, creating the effect of looking through the screen-door. In fact, this effect is sometimes present in budget models, regardless of technology. More expensive models usually use various compensation technologies to eliminate it. Some low-cost DLP projectors can display sharp color transitions (the “posterization effect”), generating digital noise when displaying a single-color field. This problem is caused by DMD chip control features. Almost all 3-chip projectors can have this problem due to the not perfect placement of the three matrices. As a result, this factor reduces the image clarity on the screen. But the optics quality affects the image clarity much more. A DLP projectors optical unit usually has a reliable seal and does not need air filters. On the other hand, other components, including the bulb and the board, require periodic cleaning from dust. Therefore, expensive DLP projectors of popular brands use filters. This video demonstrates the visualization of the rainbow effect (color artifacts along the contour of fast-moving objects) in 1-chip DLP projectors. Read the full article