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DIGITAL Image Projection

Digital Image Projection

• A digital projector, also called a digital projection display system, is a specialized computer display that projects an enlarged image on a movie screen. Such devices are commonly used in presentations.• There are two main types of digital projection display systems.

The Older, less expensive type employs three transparent liquid-crystal-display ( LCD ) panels, one for each of the primary colors (red, green, and blue). The light of each pixel varies depending on the image data received from the computer. The light from a lamp is directed through the LCD panels, collimated using a lens, and projected onto a

screen. The overall construction of the device is similar to that of a slide projector, where the "slide" consists of the three LCD panels placed close together near the focal point of the projection lens. Advantages of LCD technology

include efficiency, ease of brightness and contrast adjustment, and high image resolution .

How does LCD technology work?LCD projectors project light onto mirrors which split it up into its 3 primary colors: red, green and blue. The colors

then pass through three separate glass panels (actually prisms), which is why this technology is referred to as 3LCD. When light is projected through the LCD panels, individual pixels are opened or closed to allow light through or block

it. The separate colors are then converged using another prism and projected on to the screen.

What are the advantages of LCD Projectors?

LCD projectors have historically had three main advantages over DLP projectors.• More accurate colours• DLP projectors often have a clear section in their color wheel which boosts brightness but reduces color saturation.

LCD projectors do not have a color wheel.• Sharper image

• LCD projectors have a slightly sharper image than DLP projectors at equal resolutions. This can actually be a drawback which we will come to below.

• More light-efficient• This means that the same wattage lamp in an LCD and DLP would produce a brighter image in the LCD.

The disadvantages of LCD ProjectorsThe historical disadvantages of LCD are more relevant to video than data applications.• Screen door effect• The sharper image produced by LCD projectors can actually be a disadvantage, since the more precise focusing

makes the pixilation (“chicken wiring” or “screen door effect”) of an image more obvious.• Contrast• LCD contrast may not be as good compared to DLP, meaning that LCDs cannot produce completely black images.

Both of the above are less of a problem with newer, higher resolution 3LCD models.• Portability• LCD projectors have more parts and so are bulkier and less portable than DLPs.• Image degradation• More parts means more parts which can go wrong. LCD panels can experience long term image degradation where

colour balance shifts and overall contrast is reduced. LCD panels can be expensive to replace.• Dead pixels• Dead pixles can become a problem in LCD projectors, where one or more pixels turn permanently on or off. With

one pixel, the effect is hardly noticeable, but it can become an annoyance if this happens in clusters of pixels

A newer, more expensive scheme is known as Digital Light Processing (DLP), a proprietary technology developed by Texas Instruments. In a DLP display, tiny mirrors are used instead of transparent panels. Each mirror represents one pixel. The light, rather than passing through the panel, is reflected from it. The mirrors move back and forth, varying the amount of light that reaches the projection lens from each pixel. Color is obtained by passing the light from the

lamp through a rotating wheel with red, green, and blue filters. This subjects the mirrors to light at each of the primary colors in a rapid rotating sequence. The result is a color-modulated image that the human eye sees as

natural color. Advantages of DLP technology include light weight, high contrast, and lack of pixelation.

How does DLP technology work?Digital Light Processing is a proprietary system developed by Texas Instruments, and works differently to LCD

projection. Most DLP projectors have a single chip instead of glass panels through which light is passed, and this chip has a reflective surface composed of thousands of tiny mirrors which correspond to individual pixels. These mirrors can move back and forth when light is beamed onto the chip to direct the light from individual pixels either towards the projector lens or away from it. In order to define colours, DLP projectors have a colour wheel that consists of red, green and blue filters. This wheel spins between the light source and the DLP chip and alternates the colour of the

light hitting the chip between red, green and blue. The mirrors tilt away from or into the lens path depending on how much of each color is required for each pixel at any given moment.

What are the advantages of DLP Projectors?• DLP projectors are a favourite amongst road warriors and home theatre enthusiasts for several reasons:• Portability• DLP projectors tend to be smaller and easier to transport since they have one chip compared to the LCD’s 3 panels.• Higher Contrast• The deep blacks achievable with DLP projectors make them very popular for home cinema applications.• Reduced Pixilation• This is especially noticeable in comparisons of lower-end LCD and DLPs, and makes DLP a popular choice for

smooth video applications.• Reliability• DLPs tend to fail less often due to fewer parts and are less expensive to repair. DLP projectors have sealed optics,

making them ideal for use in dusty environments.

The disadvantages of DLP Technology• The Rainbow effect• When looking away from the projected image of a DLP projector to an off-screen object, or when looking quickly

from one side of the screen to the other, you may experience a “rainbow” effect – a momentary flash of rainbow-coloured stripes around brighter objects. This is typically only a problem in older DLP projectors without modern, faster 6-colour wheels.

• Light leakage• Some people may also experience “light leakage” from their DLP projector in the form of a grey band around the

outside of the image. This is caused by stray light reflecting off the edges of the mirrors on the DLP chip. This can be avoided by installing black borders around the screen. Again, light leakage is generally only a problem in older DLP projectors.

INSIGHTSAs an education student I am very thankful that our generation is very much literate to technologies, using educational technology is very useful and important as a future educator because it makes our work easier and comfortable, as a future educator I must possess the 21st century skills to be an effective teacher and resourceful. I must be aware of the technologies and use them accordingly. But we must not always depend on the technologies because some situations are out of control or the technologies are not available we must be an adaptor and adapt the situation and think of a way to continue on your lesson, we must be visionary and be able to attain the objectives even if your resource materials or educational materials are not available. As an education student I am a learner, I want to be know more about educational technologies.

REFERENCES:http://www.bambooav.com/the-differences-between-lcd-and-dlp-projector-technology.htmlhttp://whatis.techtarget.com/definition/digital-projector-digital-projection-display-system