GANDHINAGAR INSTITUTE OF TECHNOLOGY PREPARED BY: Mihir Hathi Komal Kumari GUIDED BY: Prof. Gunjan Jani Audio video system Active Learning Assignment

PROJECTION DISPLAY SYSTEM

Introduction  A projection screen is an installation consisting of a surface and a support structure used for displaying a projected image for the view of an audience.  Projection screens may be permanently installed, as in a movie theater; painted on the wall; or portable with tripod or floor rising models. as in a conference room or other non-dedicated viewing space.  Screens can be further designed for front or back projection, the more common being front projection systems, which have the image source situated on the same side of the screen as the audience.

Types of Projection Display System:  Rear-projection televisions System  CRT rear-projection television  LCD rear-projection television  DLP rear-projection television  Front-projection television System

Rear-projection televisions System  Rear-projection television (RPTV) is a type of large-screen television display technology. Until approximately 2005, most of the relatively affordable consumer large screen TVs up to 100 in (250 cm) used rear-projection technology.  A variation is a video projector, using similar technology, which projects onto a screen.  Rear-projection systems look more like traditional televisions.  They display images on the back of a screen and the projector is completely contained within the television itself.

 There are five basic elements in the construction of a rear-projection television.  First, there is the type of projector technology used to produce a video image.  Second, the type of lens assembly used to magnify the projected image.  Third, the necessity to employ a mirror to reflect the projected image.  Fourth, the screen upon which the reflected image is presented.  Fifth, the sealed box that contains all of the previous elements.

CRT rear-projection television  The cathode ray tube (CRT) is a vacuum tube containing one or more electron guns, and a phosphorescent screen used to view images.  It has a means to accelerate and deflect the electron beam(s) onto the screen to create the images.  Cathode ray tubes create the image by firing a beam of electrons onto a phosphor- coated screen; the image is projected onto a large screen.  The projection cathode ray tubes can be arranged in various ways.  One arrangement is to use one tube and three phosphor (red, green, blue) coatings.  Alternatively, one black-and-white tube can be used with a spinning color wheel.  A third option is to use three CRT's, one each for red, green, and blue.  The vacuum level inside the tube is high vacuum on the order of 0.01 Pa to 133 nPa.

Advantages  Achieves excellent black level and contrast ratio  Achieves excellent color reproduction  CRTs have generally very long lifetimes  Greater viewing angles than those of LCDs Disadvantages 1. Heavy and large, especially depth- wise 2. If one CRT fails the other two should be replaced for optimal color and brightness balance 3. Susceptible to burn-in because CRT is phosphor-based

LCD rear-projection television  A lamp transmits light through a small LCD chip made up of individual pixels to create an image.  The LCD projector uses dichroic mirrors to take the light and create three separate red, green, and blue beams, which are then passed through three separate LCD panels.  The liquid crystals are manipulated using electric current to control the amount of light passing through.  The lens system combines the three color images and projects them.

Advantages  Smaller than CRT projectors  LCD chip can be easily repaired or replaced  Is not susceptible to burn-in  The Screen-door effect: Individual pixels may be visible on the large screen, giving the appearance that the viewer is looking through a screen door.  Possibility of defective pixels  Poor black level  Not as slim as DLP projection television  Uses lamps for light, lamps may need to be replaced  Limited viewing angles Disadvantages

DLP rear-projection television  Digital Light Processing (DLP) is a display device based on micro-electro-mechanical technology that uses a digital micromirror device.  It was originally developed in 1987 by Dr. 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  Digital Projection and Texas Instruments were both awarded Emmy Awards in 1998 for the DLP projector technology.  It creates an image using a Digital Micromirror Device (DMD chip) that has on its surface several hundred thousand microscopic mirrors arranged in a rectangular array which correspond to the pixels in the image to be displayed.

 In the on state, light from the projector bulb is reflected into the lens making the pixel appear bright on the screen.  In the off state, the light is directed elsewhere, making the pixel appear dark.  Mirrors flip between light and dark positions, so subpixel brightness is controlled by proportionally varying the amount of time a mirror is in the bright position; its pulse-width modulation.  The mirror is made of aluminum and is mounted on a torsion-supported yoke.

InFocus IN34 DLP video projector Texas Instuments digital micromirror device (DMD chip).

Advantages  Slimmest of all types of projection televisions  Achieves excellent black level and contrast ratio  DMD chip can be easily repaired or replaced  Is not susceptible to burn-in  Better viewing angles than those of CRT projectors  Image brightness only decreases due to the age of the lamp  defective pixels are rare and no screen-door effect  Smooth (at 1080p resolution), jitter-free images  Perfect geometry and excellent grayscale linearity achievable  The use of a replaceable light source means a potentially longer life than CRTs and plasma displays  New LED and laser DLP display systems more or less eliminate the need for lamp replacement.  Lighter weight than LCD and plasma televisions  DLP projectors can process up to 7 separate colors, giving them a wider color gamut.

Disadvantages  Uses lamps for light, lamps need to be replaced on average once every year and a half to two years.  Fixed number of pixels, other resolutions need to be scaled to fit this. This is a limitation only when compared with CRT displays.  The Rainbow Effect: This is an unwanted visual artifact that is described as flashes of colored light seen when the viewer looks across the display from one side to the other.  Some viewers are bothered by the "rainbow effect" present in colour-wheel models - particularly in older models (explained above).  Rear projection DLP TVs are not as thin as LCD or plasma flat-panel displays (although approximately comparable in weight), although some models as of 2008 are becoming wall-mountable (while still being 10" to 14" thick)  Replacement of the lamp / light bulb in lamp-based units. The life span of a mercury lamp averages 2000–5000 hours and the replacement cost for these range from $99 – 350, depending on the brand and model. Newer generations' units use LEDs or lasers which effectively eliminate this issue, although replacement LED chips could potentially be required over the extended lifespan of the television set.

 Dithering noise may be noticeable, especially in dark image areas. Newer (post ~2004) chip generations have less noise than older ones.  Response time in video games may be affected by upscaling lag. While all HDTVs have some lag when upscaling lower resolution input to their native resolution, DLPs are commonly reported to have longer delays. Newer consoles such as the Wii do not have this problem as long as they are connected with HD-capable cables.  May use more electricity, and generate more heat, than competing technologies.

Rear Projection Television

Advantages  Significantly cheaper than flat-panel counterparts  Projectors that are not phosphor-based (LCD/DLP) are not susceptible to burn- in  Rear-projection is not subject to glare  Rear-projection televisions are much bulkier than flat-panel televisions  Lamp may need to be replaced after heavy usage  Rear-projection has smaller viewing angles than those of flat-panel displays Disadvantages

Comparision Between LCD, DLP and LCOS

Front-projection television System  A front-projection system uses a projector and a separate screen, and it projects images onto the front of that screen.  The projector can be placed on a table or mounted to the ceiling.  The picture looks best when displayed on a high-quality screen, but a specially painted, flat wall will work as well.

Advantages  Front-projection picture quality approaches that of movie theater  Front-projection televisions take up very little space because a projector screen is extremely slim, and even a suitably prepared wall can be used  Display size can be extremely large, typically limited by room height.  Front-projection more difficult to set up because projector is separate and must be placed in front of the screen, typically on the ceiling  Lamp may need to be replaced after heavy usage  Image brightness is an issue, may require darkened room. Disadvantages