Transcript PPT
CSCI-235 Micro-Computers in Science Hardware Part II • Digitizing the Real World Scanner Digital camera Speech recognition Sensing devices Audio and video digitizers • Continuous & Discrete Signals • Representing Sounds Computers are capable of representing much more than numbers and text EXAMPLE: representing sounds • Sounds are inherently analog signals with specific amplitudes and frequencies • When sound waves reach your ear, they cause your eardrum to vibrate, and your brain interprets the vibration as sound • Analog waveforms must be converted to a sequence of discrete values Digital sampling is the process in which the amplitude of a wave is measured at regular intervals, and stored as discrete measurements Frequent measurements must be taken to ensure high quality (e.g., 44,100 readings per second for a CD) • This results in massive amounts of storage • Techniques are used to compress the data and reduce file sizes (e.g., MP3, WAV) • Audio Input Computers can accept input from a microphone An expansion card called a sound card records and plays back sound files A sound card has 2 functions • Play previously recorded sound (translates a digital file into sound) • To record new sound (translate sound into a digital file) Sound files contain digitized sound data Popular sound file formats include: • • • • Windows WAV Moving Pictures Expert Group (MPEG) MP2 and MP3 Musical Instrument Digital Interface (MIDI) • Audio Digitizers Audio digitizers capture spoken words, music and sound effects and convert them to digitized sounds These sounds can be stored in a computer’s memory and modified with computer software • Representing Images Images are stored using a variety of formats and compression techniques The simplest representation is a bitmap Bitmaps partition an image into a grid of picture elements, called pixels, and then convert each pixel into a bit pattern Resolution refers to the sharpness or clarity of an image • Bitmaps that are divided into smaller pixels will yield higher resolution images • The left image is stored using 96 pixels per square inch, and the right image is stored using 48 pixels per square inch • The left image appears sharp, but has twice the storage requirements When creating a bitmap of a color image, more than one bit is required to represent each pixel • The most common system is to translate each pixel into a 24 bit code, known as its RGB value: 8 bits to represent the intensity of each red/green/blue component • Common image formats implement various compression techniques to reduce storage size GIF (Graphics Interchange Format) • A lossless format, meaning no information is lost in the compression • Commonly used for precise pictures, such as line drawings JPEG (Joint Photographic Experts Group) • A lossy format, so the compression is not fully reversible (but more efficient) • Commonly used for photographs • Video Digitizers Video digitizers capture input from video sources such as video camera and convert it to a digital signal that can be stored in memory and displayed on a computer screen • Data Representation Binary Numbers!!! • Sound pitch number binary number • Letter number binary number • Image color at each pixel number binary number But how many bits are needed to store n symbols? Or, how many bits are needed to represent n numbers? log2n • Output Devices: Engaging our Senses Output devices are peripheral devices that enable us to view or hear the computer’s processed data • Visual output – Text, graphics, and video • Audio output – Sounds, music, and synthesized speech • Monitors A monitor is a peripheral device which displays computer output on a screen Types of monitors: • Cathode-ray tube (CRT) • Liquid Crystal Display (LCD or flat-panel) CRT LCD • Screen Talk Monitor size - measured as a diagonal line across the screen Pixels (or picture element) - tiny dots that compose a picture Resolution - the number of pixels displayed on the screen (the higher the resolution, the closer together the dots) • Printers A printer is a peripheral device that produces a physical copy or hard copy of the computer’s output Inkjet printer makes characters by inserting dots of ink • Letter-quality printouts • Cost of printer is inexpensive but ink is costly Laser printer works like a copier • Quality determined by dots per inch (dpi) produced • Color printers available • Expensive initial costs but cheaper to operate per page • Storage Technologies Magnetic – Storage devices that use disks or tapes that are coated with magnetically sensitive material Optical – Storage devices that use laser beams to read patterns etched into plastic disks • Optical Disk Storage Microscopic indentations called pits scatter the laser beam’s light. A light-sensing device receives no light from the pits. A signal is sent to the computer corresponding to a 0 in the binary system Flat, reflective areas, called lands, bounce the light back to the light sensing device, which sends a signal corresponding to a 1 Cross-section of a disk Disk surface magnified • CD-R and CD-RW Discs and Recorders CD-R • Discs can be read and written to • Discs can only be written to “once” • CD-R drives are capable of reading and writing data CD-RW • Discs can be read and written to • Discs are erasable • Discs can be written to many times • CD-RW drives are capable of reading, writing, and erasing data