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Chapter 7 Input/Output Technology

Chapter 7 Input/Output Technology. 240. Communications between people and computers Manual Input Devices Keyboard

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Chapter 7 Input/Output Technology

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  1. Chapter 7Input/Output Technology 240 Communications between people and computers Manual Input Devices Keyboard Keystrokes generate electrical signals (scan code) Controller (microprocessor) covert signal to digital code Code used for lookup table – determine command Software program is executed dependent upon command Pointing Devices Mouse, trackball, joystick, digitizer tablet Translate spatial position of one point to another into digital code Movement generates signals sent to controller Controller coverts analog signal to digital number Software determines the action dependent upon the digital number Digitizers: A pen or stylus and a digitizing tablet Tablet is sensitive to the placement of the stylus at any point on its surface 240

  2. Print and Display Matrix-Oriented Image Composition Display surface is divided into rows and columns Each matrix cell = one component of an image Picture Element (pixel) = one component of an image Printing: a pixel is empty or contains one or more inks or dyes Pixel size is the smallest drop of ink that can be accurately placed on the page Display: a pixel is empty or display light of varying color and intensity Number of pixels depends upon surface size (Height and width) and size of pixel Typical pixel size (pitch) = .2 and .3 millimeters (thousandths of a meter) Example: 300 x 200 image size = 60,000 pixels 300 rows, 200 columns Pixel pitch .3 millimeters 300 x .3 = 90 mm height 200 x .3 = 60 mm width 90 x 60 = 5,400 mm2 total Smaller the pixel the higher the quality displayResolution: number of pixels displayed per linear measurement unit 243

  3. Print and Display Font: a collection of characters of similar style and appearance Point: Measurement of a font size The distance between the top of the highest character to the bottom of the lowest character in the font Color: Any color can be represented as a mixture of varying intensities of colors Computer displays: red, green, blue (RGB) combinations Pixel Content: Described numerically bit map: set of pixel descriptions Monochrome (black & white) display Single bit (on or off) Grayscale Shades of gray between pure black and pure white Number of shades depends upon the number of bits used to represent a single pixel Chromatic depth (chromatic resolution): the number of distinct colors or gray shades that can be displayed 4 bits to represent the color/shade of a pixel = 16 colors/shades8 bits to represent the color/shade of a pixel = 256 colors/shades 244 245

  4. Print and Display Color displays 3 numbers to represent a pixel color Colors are red, green, and blue (RGB) Each number represent the intensity of a color format: red#:green#:blue# 255:230:25 Sample: 8 bits to identify a single color intensity 3 colors x 8 bits = 24 bits = 224 = 16,777,216 color combinations Palette: table of colors identified by a number Dithering: applying multiple amounts of one color in a single pixel area Sample: A device (i.e. Inkjet printer) can place four (4) different intensities of a single color in one (1) pixel different intensities = 4 colors = 3 (RGB) 43 = 64 different colors can be generated 246 247 246

  5. Print and Display Image Storage Requirements Memory required to store an image is dependent upon: Number of bits used to represent a pixel intensity/color Image height (in pixels) Image width (in pixels) Sample: 1) Determine total image size in pixels Image has 800 rows Image has 600 columns 800 x 600 = 480,000 pixels for the total image 2) Determine memory required to store the image Monochrome Each pixel is represented by a single bit Formula: # of pixels divided by # of bits in a byte 480,000 / 8 bits = 60,000 bytes of storage Color Each pixel is represented by 3 bytes (RGB) Formula: # of pixels X # of bytes to store the color 480,000 pixels x 3 bytes = 1,440,000 bytes of storage 1.4 million bytes 247

  6. Image Compression Techniques Common techniques Static images Graphics Interchange Format (GIF) Joint Photographic Experts Group (JPEG, JPG) Moving images Moving Pictures Experts Group (MPEG, MPG) Image Description Languages (IDL) Bit map drawbacks 1) Require large amounts of storage 2) No standard storage format - are device dependent for displaying IDL resolve these issues Vector: a line segment that has a specific angle and length with respect to a point of origin Vector lists: a group of vector descriptions that define a drawing Advanced Image Description Languages (AIDL) Can describe complex images such as shapes and fonts. Display list: describes an image as a collection of display objects such as circles, triangles, rectangles Adobe’s PostScript and HP Printer Control Language (PCL) 247 248 Sample 249 Sample 251

  7. Video Display Graphics Video Display Devices Monitors Controlled by a video controller Data is converted by the controller from digital to analog Analog signals display data to the screen 252

  8. Printers Dot Matrix Mechanical contact between ink and paper Print head Columns and rows of pins Pins selected (fired) create a pattern (character) on the paper Motor moves paper (form fed) Paper moves on sprockets Generally poor output quality Noisy operation Good for preprinted forms Ink Jet Print single unattached sheets of paper No direct physical contact between print head and paper Print head has nozzle opening similar to the dot matrix pins Electrical charge shoots ink out of the nozzle openings Very close proximity to the paper 256 257

  9. Printers Laser Printers No print head No ink ribbon 1) A rotating drum is lightly charged 2) Print driver writes the contents of the printer buffer (via laser) to the rotating drum 3) Repeat step 2) until entire buffer is on the drum 4) The drum rotates past the an arm where toner is applied Charged areas receive toner (ink) Uncharged areas do not receive toner (ink) 5) Paper is moved and synchronized with the drum rotation 6) The paper is given a high electric charge 7) The toner on the drum is attracted to the charged paper 8) The paper (with toner attached) is fed through heated rollers which fuse the toner to the paper 9) Another arm removes the charge from the drum 10) Excess toner is removed from the drum Color laser printers use a separate laser, drum, and laser modulators for each color 258 258 Fig 7-11

  10. Mark Sensors and Bar Code Scanners Optical devices Mark Sensors Scan for light or dark marks at specific locations Locations are marked on the page with circles or boxes Preprinted bars on the edge of the page to establish reference points Bar Code Readers Series of vertical bars Varying thickness Varying space between bars There are numerous ‘variations’ for formats Bar widths and spacing must be very precise 260

  11. Audio I/O Devices Sound is analog data Computers use digital data Sampling: converting analog sound waves to digital representation The audio spectrum is analyzed many times per second then converted to a digital number Sound characteristics Frequency – pitch (distinct separate notes on a piano) Human frequency identification: 20 Hz to 20KHz Must be sampled at lease 40,000 per second to get an accurate representation 16 bit sample minimal for human quality Intensity - loudness Storage requirement computation 262

  12. Audio I/O Devices Formula: storage bytes per second (sample rate x (bytes per = (total storage bytes per second) sample) per second) 48,000 x 2 = 96,000 Formula: storage bytes per minute (Total storage bytes x 60 seconds = (total storage bytes per second) per minute) 96,000 x 60 = 56,760,000 Storage bytes per hour of sound sampled (total storage bytes x 60 minutes = (total storage bytes per minute) per hour) 56,760,000 x 60 = 3,405,600,000 3.4 billion bytes 262misprint in book: .0125 should be .125

  13. Audio I/O Devices Speech Recognition Phonemes: a series of individual sounds Analog sound captured (sampling) and converted to digital Digital result cross-referenced to a digital library of sounds Digital Signal Processor Specialized CPU Usually in sound cards Process streams of audio or graphical data Audio Response Unit Generates spoken messages based on textual input Problems: Frequency and pitch problems Voice input changes (get a cold) 263 265

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