Lecture #5: презентация

Lecture #5: Data Formats

Data Formats Computers Process and store all forms of data in binary format Human communication Includes language, images and sounds Data formats: Specifications for converting data into computer-usable form Define the different ways human data may be represented, stored and processed by a computer

Sources of Data Binary input Begins as discrete input Example: keyboard input such as A 1+2=3 math Keyboard generates a binary number code for each key Analog Continuous data such as sound or images Requires hardware to convert data into binary numbers

Common Data Representations

Internal Data Representation Reflects the Complexity of input source Type of processing required Trade-offs Accuracy and resolution Simple photo vs. painting in an art book Compactness (storage and transmission) More data required for improved accuracy and resolution Compression represents data in a more compact form Metadata: data that describes or interprets the meaning of data Ease of manipulation: Processing simple audio vs. high-fidelity sound Standardization Proprietary formats for storing and processing data (WordPerfect vs. Word) De facto standards: proprietary standards based on general user acceptance (PostScript)

Data Types: Numeric Used for mathematical manipulation Add, subtract, multiply, divide Types Integer (whole number) Real (contains a decimal point) Covered in Chapters 4 and 5

Data Types: Alphanumeric Alphanumeric: Characters: b T Number digits: 7 9 Punctuation marks: ! ; Special-purpose characters: $ & Numeric characters vs. numbers Both entered as ordinary characters Computer converts into numbers for calculation Examples: Variables declared as numbers by the programmer (Salary$ in BASIC) Treated as characters if processed as text Examples: Phone numbers, ZIP codes

Alphanumeric Codes Arbitrary choice of bits to represent characters Consistency: input and output device must recognize same code Value of binary number representing character corresponds to placement in the alphabet Facilitates sorting and searching

Representing Characters ASCII - most widely used coding scheme EBCDIC: IBM mainframe (legacy) Unicode: developed for worldwide use

ASCII Developed by ANSI (American National Standards Institute) Represents Latin alphabet, Arabic numerals, standard punctuation characters Plus small set of accents and other European special characters ASCII 7-bit code: 128 characters

ASCII Reference Table

EBCDIC Extended Binary Coded Decimal Interchange Code developed by IBM Restricted mainly to IBM or IBM compatible mainframes Conversion software to/from ASCII available Common in archival data Character codes differ from ASCII

Unicode Most common 16-bit form represents 65,536 characters ASCII Latin-I subset of Unicode Values 0 to 255 in Unicode table Multilingual: defines codes for Nearly every character-based alphabet Large set of ideographs for Chinese, Japanese and Korean Composite characters for vowels and syllabic clusters required by some languages Allows software modifications for local-languages

Collating Sequence Alphabetic sorting if software handles mixed upper- and lowercase codes In ASCII, numbers collate first; in EBCDIC, last ASCII collating sequence for string of characters

2 Classes of Codes Printing characters Produced on the screen or printer Control characters Control position of output on screen or printer Cause action to occur Communicate status between computer and I/O device

Control Code Definitions

Keyboard Input Scan code Two different scan codes on keyboard One generated when key is struck and another when key is released Converted to Unicode, ASCII or EBCDIC by software in terminal or PC Advantage Easily adapted to different languages or keyboard layout Separate scan codes for key press/release for multiple key combinations Examples: shift and control keys

Other Alphanumeric Input OCR (optical character reader) Scans text and inputs it as character data Used to read specially encoded characters Example: magnetically printed check numbers General use limited by high error rate Bar Code Readers Used in applications that require fast, accurate and repetitive input with minimal employee training Examples: supermarket checkout counters and inventory control Alphanumeric data in bar code read optically using wand Magnetic stripe reader: alphanumeric data from credit cards Voice Digitized audio recording common but conversion to alphanumeric data difficult Requires knowledge of sound patterns in a language (phonemes) plus rules for pronunciation, grammar, and syntax

Image Data Photographs, figures, icons, drawings, charts and graphs Two approaches: Bitmap or raster images of photos and paintings with continuous variation Object or vector images composed of graphical objects like lines and curves defined geometrically Differences include: Quality of the image Storage space required Time to transmit Ease of modification

Bitmap Images Used for realistic images with continuous variations in shading, color, shape and texture Examples: Scanned photos Clip art generated by a paint program Preferred when image contains large amount of detail and processing requirements are fairly simple Input devices: Scanners Digital cameras and video capture devices Graphical input devices like mice and pens Managed by photo editing software or paint software Editing tools to make tedious bit by bit process easier

Bitmap Images Each individual pixel (pi(x)cture element) in a graphic stored as a binary number Pixel: A small area with associated coordinate location Example: each point below represented by a 4-bit code corresponding to 1 of 16 shades of gray

Bitmap Display Monochrome: black or white 1 bit per pixel Gray scale: black, white or 254 shades of gray 1 byte per pixel Color graphics: 16 colors, 256 colors, or 24-bit true color (16.7 million colors) 4, 8, and 24 bits respectively

Storing Bitmap Images Frequently large files Example: 600 rows of 800 pixels with 1 byte for each of 3 colors ~1.5MB file File size affected by Resolution (the number of pixels per inch) Amount of detail affecting clarity and sharpness of an image Levels: number of bits for displaying shades of gray or multiple colors Palette: color translation table that uses a code for each pixel rather than actual color value Data compression

GIF (Graphics Interchange Format) First developed by CompuServe in 1987 GIF89a enabled animated images allows images to be displayed sequentially at fixed time sequences Color limitation: 256 Image compressed by LZW (Lempel-Zif-Welch) algorithm Preferred for line drawings, clip art and pictures with large blocks of solid color Lossless compression

GIF (Graphics Interchange Format)

JPEG (Joint Photographers Expert Group) Allows more than 16 million colors Suitable for highly detailed photographs and paintings Employs lossy compression algorithm that Discards data to decreases file size and transmission speed May reduce image resolution, tends to distort sharp lines

Other Bitmap Formats TIFF (Tagged Image File Format): .tif (pronounced tif) Used in high-quality image processing, particularly in publishing BMP (BitMaPped): .bmp (pronounced dot bmp) Device-independent format for Microsoft Windows environment: pixel colors stored independent of output device PCX: .pcx (pronounced dot p c x) Windows Paintbrush software PNG: (Portable Network Graphics): .png (pronounced ping) Designed to replace GIF and JPEG for Internet applications Patent-free Improved lossless compression No animation support

Object Images Created by drawing packages or output from spreadsheet data graphs Composed of lines and shapes in various colors Computer translates geometric formulas to create the graphic Storage space depends on image complexity number of instructions to create lines, shapes, fill patterns Movies Shrek and Toy Story use object images

Object Images Based on mathematical formulas Easy to move, scale and rotate without losing shape and identity as bitmap images may Require less storage space than bitmap images Cannot represent photos or paintings Cannot be displayed or printed directly Must be converted to bitmap since output devices except plotters are bitmap

Popular Object Graphics Software Most object image formats are proprietary Files extensions include .wmf, .dxf, .mgx, and .cgm Macromedia Flash: low-bandwidth animation Micrographx Designer: technical drawings to illustrate products CorelDraw: vector illustration, layout, bitmap creation, image-editing, painting and animation software Autodesk AutoCAD: for architects, engineers, drafters, and design-related professionals W3C SVG (Scalable Vector Graphics) based on XML Web description language Not proprietary

PostScript Page description language: list of procedures and statements that describe each of the objects to be printed on a page Stored in ASCII or Unicode text file Interpreter program in computer or output device reads PostScript to generate image Scalable font support Font outline objects specified like other objects

PostScript Program

Representing Characters Characters stored in format like Unicode or ASCII Text processed and stored primarily for content Presentation requirements like font stored with the character Text appearance is primary factor Example: screen fonts in Windows Glyphs: Macintosh coding scheme that includes both identification and presentation requirement for characters

Bitmap vs. Object Images

Video Images Require massive amount of data Video camera producing full screen 640 x 480 pixel true color image at 30 frames/sec 27.65 MB of data/sec 1-minute film clip 1.6 GB storage Options for reducing file size: decrease size of image, limit number of colors, reduce frame rate Method depends on how video delivered to users Streaming video: video displayed as it is downloaded from the Web server Example: video conferencing Local data (file on DVD or downloaded onto system) for higher quality MPEG-2: movie quality images with high compression require substantial processing capability

Audio Data Transmission and processing requirements less demanding than those for video Waveform audio: digital representation of sound MIDI (Musical Instrument Digital Interface): instructions to recreate or synthesize sounds Analog sound converted to digital values by A-to-D converter

Waveform Audio

Sampling Rate Number of times per second that sound is measured during the recording process. 1000 samples per second = 1 KHz (kilohertz) Example: Audio CD sampling rate = 44.1KHz Height of each sample saved as: 8-bit number for radio-quality recordings 16-bit number for high-fidelity recordings 2 x 16-bits for stereo

MIDI Music notation system that allows computers to communicate with music synthesizers Instructions that MIDI instruments and MIDI sound cards use to recreate or synthesize sounds. Do not store or recreate speaking or singing voices More compact than waveform 3 minutes = 10 KB

Audio Formats MP3 Derivative of MPEG-2 (ISO Moving Picture Experts Group) Uses psychoacoustic compression techniques to reduce storage requirements Discards sounds outside human hearing range: lossy compression WAV Developed by Microsoft as part of its multimedia specification General-purpose format for storing and reproducing small snippets of sound

.WAV Sound Format

Data Compression Compression: recoding data so that it requires fewer bytes of storage space. Compression ratio: the amount file is shrunk Lossless: inverse algorithm restores data to exact original form Examples: GIF, PCX, TIFF Lossy: trades off data degradation for file size and download speed Much higher compression ratios, often 10 to 1 Example: JPEG Common in multimedia MPEG-2: uses both forms for ratios of 100:1

Compression Algorithms Repetition 0 5 8 7 0 0 0 0 3 4 0 0 0 0 1 5 8 7 0 4 3 4 0 3 Example: large blocks of the same color Pattern Substitution Scans data for patterns Substitutes new pattern, makes dictionary entry Example: 45 to 30 bytes plus dictionary Peter Piper picked a peck of pickled peppers.  t   p    a   of  l   pp  s.

Internal Computer Data Format All data stored as binary numbers Interpreted based on Operations computer can perform Data types supported by programming language used to create application

5 Simple Data Types Boolean: 2-valued variables or constants with values of true or false Char: Variable or constant that holds alphanumeric character Enumerated User-defined data types with possible values listed in definition Type DayOfWeek = Mon, Tues, Wed, Thurs, Fri, Sat, Sun Integer: positive or negative whole numbers Real Numbers with a decimal point Numbers whose magnitude, large or small, exceeds computer’s capability to store as an integer