Input & Output DevicesDisplay DevicesKocaeli University Computer EngineeringAdvanced Computer Graphics
Input DevicesAlphanumeric Input Keyboards2D Inputs (Joystick, Mouse, etc)3D InputsGlove, Space, ballImage InputsCamera, Scanner
Output Graphic DevicesColor Raster CRTCalligraphic (vector) CRTFlat-panel displays:Color LCD (Liquid Crystal) Plasma DisplayHardcopy DevicesPrinters
CRTCathode Ray TubeEnclosed vacuum tube; electron beam is focused toward front surface of the tube, which is coated in phosphorSingle gun for monochrome and three guns for colorHigh voltage reduces the electron density and thus brightnessVertical and horizantal reflection plates
CRT -ContTechnology relatively old; has disadvantagesPhysical size and weightPower consumptionRandom scan display (Vector Display) & Rater scan display
Vector DisplaysRandom scan displayAlso called vector, stroke-writing, or calligraphic displays.
The electron beam directly draws the picture in any specified order. A pen plotter is an example of such a system
Raster DisplaysThe image is stored in a frame buffer containing the total screen area and where each memory location corresponds to a pixel.In a monochrome system, each bit is 1 or 0 for the corresponding pixel to be on or off (bitmap).Image is represented as a bitmap (1 bit/pixel) or as a pixmap (8 or 24 bits/pixel)
A raster-scan system displays an object as a set of points across each screen scan line(a)(b)(d)(c)
Buffers in Raster DisplayImage description is stored in a memory area called refresh buffer or frame bufferThe video controller sweeps the beam across the screen, one row at a time, from top to bottom and back to the top again.Three beams are controlled (red, green, blue) and the intensity of each color is stored in the frame bufferTo give an idea: refreshing is carried out at the rate of 60 to 80 frames/second
Buffers in Raster Display
Buffers in Raster Display
N-bit plane Frame bufferChoice of the number of gray scales and colors depend on the value of N (bit plane size)N = 1 two colors (B&W)N = 3 8 gray scales or colorsN = 8 256 gray scales or colorsN = 24 16 million colours
A single bit-plane frame BufferFor colored displays (raster-scan), three separate color guns must be used.Each bit plane drives a color gun
An N-bit plane gray level frame buffer
Simple color frame buffer
N-bit plane gray level Frame bufferIn case of one-bit for each color frame buffer, we get 8 colors
LCDContains matrix of liquid crystals sandwiched between two polarizing filter panelsActive and passive matrix displaysManufactured with thin film transistor (TFT) technologyCompared with CRTsLess contrastReduced size, weight, and power consumptionHigher costenergy-efficient, have sharp pictureContrast: how big the difference between "white" and "black"
Plasma DisplayCombine elements of CRT and LCD technologyFlat panel, active matrix devicesActively generate colored light near surface of the display; good brightness and viewingRequire more power than LCDs, less than CRTsShortcomingsLimited operational lifetimeLarger pixel size reduces comparative image quality when viewed from short distances
How Plasma Display WorksPlasma displays have no backlight and no color filters; each pixel contains a gas that emits ultraviolet light when electricity is applied.
Plasma Plasma technology consists of hundreds of thousands of individual pixel cells, which allow electric pulses to excite rare natural gases-usually xenon and neon-causing them to glow and produce light. This light illuminates the proper balance of red, green, or blue phosphors contained in each cell to display the proper color sequence from the light. Each pixel cell is essentially an individual microscopic florescent light bulb, receiving instruction from software contained on the rear electrostatic silicon board. Look very closely at a plasma TV and you can actually see the individual pixel cell coloration of red, green, and blue bars. You can also see the black ribs which separate each.
LED TVLED (light emitting diode)LED TVs are a new form of LCD Television. The panel on an LED TV is still an LCD TV panel and operates with the same twisting crystals matrix. The backlight is the difference - changing from fluorescent to LED based backlightingHave better contrast and more accurate colors than LCD
Digital Images from Scanners and CamerasThe color and brightness of each tiny area seen by a sensor is "sampled", meaning the color value of each area is measured and recorded as a numeric value which represents the color there
Each one of these sampled numeric color data values is called a pixel
A 6 inch photograph scanned at 100 dpi will produce 600 pixels across that dimension of the image.
The scanner scanning resolution (pixels per inch) and the size of the area being scanned (inches) determine the image size (pixels) created from the inches scanned.If we scan 8x10 inch paper at 300 dpi, we will create (8 inches x 300 ppi) x (10 inches x 300 ppi) = 2400x3000 pixels
For the past 75 years, the vast majority of televisions have been built around the same technology: the cathode ray tube (CRT). In a CRT television, a gun fires a beam of electrons (negatively-charged particles) inside a large glass tube. The electrons excite phosphor atoms along the wide end of the tube (the screen), which causes the phosphor atoms to light up. The television image is produced by lighting up different areas of the phosphor coating with different colors at different intensities.**Actually, LCD images are inferior to CRT images, color uniformity, image sharpness and viewing angle are poor compared to a CRT and fast moving images appear blurred because the crystals can't quite keep up and react quickly enough. They are getting better, but will never beat the image quality of a CRT. But obviously are smaller and lighter, so it's worthing having one anyway
*The two transparent panels are polarised, which means they will only pass light waves in one plane. These two polarised panels at 90 to each other so that light filtered from one plane cannot get through the other panel because it only lets light through in a plane at 90 to the first plane. So the panel appears to be "black" (or at least very dark). However, when electricity is applied to one of the segments of liquid crystals (segments are switched on and off to form the images you see on the screen). The crystals line up in such a way as to make the light turn through 90 in between the two panels. So now the light "TWISTS" through the panels and is visible on the other side. Does having a "Super-Twist" display mean more to you now?
*The basic idea of a plasma display is to illuminate tiny, colored fluorescent lights to form an image. Each pixel is made up of three fluorescent lights -- a red light, a green light and a blue light. Just like a CRT television, the plasma display varies the intensities of the different lights to produce a full range of colors. On the next page, learn how the plasma works*Xenon and neon atoms, the atoms used in plasma screens, release light photons when they are excited*This is not a new display technology. LED TVs are actually just LCD HDTVs that use an LED backlight instead of a conventional fluorescent one.
While the display technology is the same, these "LED-LCD" TVs generally have better contrast and more accurate colors than fluorescent-backlit models.***