Transcript Book Title
CSCI-235 Micro-Computer Applications 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 to ensure high quality (e.g., 44,100 readings per second for a CD) • This results in massive amounts of storage • Techniques to compress the data and reduce file sizes (e.g., MP3, WAV) Figure 4.6 Recovery of a sampled sine wave for different sampling rates Audio Input Computers can accept input from a microphone An expansion card called a sound card records and plays back sound files 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 Input: Speech Recognition Speech recognition is a type of input in which the computer recognizes words spoken into a microphone Special software and a microphone are required Latest technology uses continuous speech recognition where the user does not have to pause between words 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 Digital Input: Digital Cameras and Digital Video Digital Video Digital Cameras 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 CRT LCD 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) Cathode-ray tube (CRT) Resemble televisions Use picture tube technology Less expensive than a LCD monitor Take up more desk space and use more energy than LCD monitors 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) Monitor Specifications Screen size – The diagonal measurement of the screen surface in inches (15, 17, 19, 21) Resolution – The sharpness of the image determined by the number of horizontal and vertical dots (pixels) that the screen can display (800 x 600, 1024 x 768, 1600 x 1200) Refresh rate – The speed at which the screen is redrawn (refreshed) and measured in Hertz (Hz) (60Hz, 75Hz) Image Quality Image quality is affected by resolution and color depth (or bit depth) Color depth refers to the number of different colors a monitor displays at the same time Printers A printer is a peripheral device that produces a physical copy or hard copy of the computer’s output Types of Printers Laser Inkjet Inkjet printer, also called a bubble-jet, makes characters by inserting dots of ink onto paper 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 Devices Storage devices are categorized by: The type of operations they perform The method they use to access the information The technology they use Their location in the storage hierarchy Their capacity and speed Sequential vs. Random Access Storage Hard Disk – Tape Drive – Floppy Disk Drive – sequential storage random-access storage random-access storage – Storage devices that read and write data in a serial (one after the other) fashion Sequential – Storage devices that read and write data without going through a sequence of locations Random-Access Storage Technologies: Magnetic and OpticalOptical Storage – Magnetic Storage CD/DVD drive – Storage devices 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 Magnetic Magnetic Disk Storage A disk is formatted; it is divided into tracks and sectors, and a file allocation table (FAT) is created Track – circular band Sector – pie shaped section Cluster – two or more adjacent sectors FAT – keeps track of specific locations of files Track Sector Cluster Optical Disk Storage Cross-section of a disk Disk surface magnified 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 CD-ROM Discs and Drives CD-ROM stands for Compact Disc-Read Only Memory CD-ROM drives can not write data to discs They are capable of storing ~700 MB of data They are used for storing operating systems, large application programs, and multimedia programs 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 DVD-ROM Discs and Drives DVD stands for Digital Video Disc DVD technology is similar to CDROM technology DVDs are capable of storing up to 17GB of data The data transfer rate of DVD drives is comparable to that of hard disk drives DVD-R and DVD-RW drives have the ability to read/write data