ICT Chapter 3: Number Systems, Encoding, and Multimedia

3.1 number system and representation - - A\) Unit of data Bit - the most basic unit of data. Byte - 1B = 8 bits Kilobyte - 1KB = 1024 B Megabyte - 1MB = 1024KB Gigabyte - 1GB = 1024MB Terabyte - 1TB = 1024GB Bitrate / data transfer rate : the amount of data transferred per unit time in...

3.1 number system and representation - - A\) Unit of data Bit - the most basic unit of data. Byte - 1B = 8 bits Kilobyte - 1KB = 1024 B Megabyte - 1MB = 1024KB Gigabyte - 1GB = 1024MB Terabyte - 1TB = 1024GB Bitrate / data transfer rate : the amount of data transferred per unit time in data transmission system Bit per second(bps) - one bit of data is transferred every second Kilobit per second(kbps) - 1 kbps = 1000 bps Megabit per second(mbps) - 1 mbps = 1000 kbps Gigabit per second(gbps) - 1 gbps = 1000 mbps Terabit per second(tbps) - 1 tbps = 1000 gbps Units of data - usually binary based , units of bitrate - usually decimal based B\) Binary number - - C\) Hexadecimal number Decimal: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Hexadecimal: 1 2 3 4 5 6 7 8 9 A B C D E F (after F there's no more) D\) representation of unsigned integers - Two's complement - - F\) Overflow error Occurs when result of calculations is out of range, thus results will be wrong 3.2 Character encoding A\) English American Standard Code for Information Exchange (ASCII) - - - Sometimes, ASCII is extended to 8 bits (1 byte) because - - - Since the storage size of ASCII is small, it is still used nowadays Characteristics of ASCII - - B\) Chinese There are two sets of chinese characters - - (both use 2 bytes (16 bits) to store and contain over 10k characters) Both encoding systems represent Chinese, but they aren't interchangeable. So if a text file or website is encoded by big-5 but is decoded by Guobiao, instead of being translated, the text will be displayed as garbled text. (traditional code does not share the same code as simplified code) C\) Multi-language Unicode - - - (due to the large number of unicode characters, it may use up to 4 bytes, depending on the language) 3.3 Barcode encoding A\) barcode - - Scanning a barcode - only area covered by the red line (from scanner) is scanned , so the height of the bars don\'t matter , only width and space matters A readable barcode must - B\) Quick Response Code (QR code)  Comparison between QR code and barcode Technology enables both to be scanned by a smartphone with specific applications installed Barcode - - - - QR code - - - - QR codes can still be scanned even if - - - - - - (This shows how high the error correction capability a QR code has is) 3.4 analog and digital data - - Comparison between analog and digital data Analog data - - - - - Digital data - - - - A\) Digitalisation - conversion of analog to digital data - -  Now the signals are stored as a sequence of integers, this sequence is digital data Example of digitalisation of text and images - converting Physical books to electronic books 3.5 multimedia Introduction to file Format Multimedia can be stored in various file formats and have different attributes Most of the time, the file Format is indicated by its file extension (.txt ,.png etc) But changing the name of the file does not change the file format, to change the file format properly, we should use an editing software to export the file in another file format or use a file format converting software Compression since Multimedia files tend to have a larger size, they are usually compressed to allow file transmission and save storage There are many compression methods and the essential details of the compression method are usually stored in the file header to help the computer decompress the file - - Compression ratio : uncompressed size / compressed size File size calculation : file size per character x number of characters File formats for plain text - File formats for formatted texts - - - - A text file format is not tied to any character encoding system, it\'s possible to change the character encoding system as much as we want B)Image An image file has 4 important attributes : resolution, color depth, aspect ratio, transparency Color Depth - number of bits used to represent the color of a pixel 8-bit color - more details and shading 3-bit color - colors are flat with not much detail 3-bit grayscale - shades of gray 1-bit color - black and white Resolution - total number of pixels in an image High resolution - clear and detailed (vector) Low resolution - pixels (bitmap) Aspect ratio - ratio of width to height Transparency - whether the image can be / have transparent Areas or not A digital image in a format that doesn\'t support transparency Is always rectangle C)Audio 3 important attributes : bit depth, sampling rate, the number of channels Bit depth - number of bits used to represent an audio sample, the higher the bit depth, the more sound levels it can represent and better the quality High bit depth = 50 levels between -100 and 150 medium bit depth = 25 levels Low bit depth = 10 levels Sampling rate - number of audio samples taken per second Higher sampling rates means the audio is closer To the original soundwave and better quality Number of channels - sometimes an audio file has more than one channel (stereo audio has 2 channels while 5.1 surround sound has more than 2)