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DAVJ277 1.2.4

J277 GCSE CS 1.2.4 b) characters, sound and images

QuestionAnswer
Define a Character set All the characters which are recognised/UNDERSTOOD/can be represented by the computer system. Includes upper and lower case, numbers and symbols on the keyboard.
How does ASCII or Unicode represent text in a computer system 1) Each character is given a unique numeric code including symbols, digits, upper and lower case 2) This code is then stored in binary 10101011 3) Each character takes 1 byte (ascii) or 2 bytes (Unicode) 4) Text is stored as a series of bytes (1 per character ascii) – (2 bytes per character Unicode) 5) Some codes are reserved for control characters (eg TAB, Carriage Return) 6) As ASCII has more bits per character more characters can be stored. All alphabets in the world.
What is the relationship between the number of bits per character and the number of characters in a set (ASCII V UNICODE) ASCII - 1 byte 01010101, Unicode 2 bytes 01010101 10101111 ASCII - smaller character set - 128/256 combinations - Unicode larger character set - 65,536 combinations ASCII - can represent UK alphabet, numbers, symbols and control characters UNICODE - Can represent foreign alphabets, thousands of symbols and EMOJIS
How are bitmap pictures stored on a computer? An image is made up of/consists of pixels Each pixel has a binary number that represents its colour. Each colour has a unique binary number The more bits that are used to store each pixel, the more colours are potentially available. This is known as colour depth.
What is metadata? Data about data. Additional data stored with an image including information such as: Width and height of image in pixels Number of bits per pixel (colour depth). Colour palette. Without this the computer will not know how to display the image
Resolution Resolution is the concentration of pixels or the number of pixels. The higher the resolution the more pixels are required for the picture which will increase the size of the bitmap file.
What is the effect of colour depth on the size of an image file The greater the colour depth the greater the file size as each pixel will require more bits of storage. For an image of height and width 64 x 64 64x64 at 1 bit colour = 4096 bits 64x64 at 8 bit colour = 32,768 bits.
What is colour depth? The number of bits assigned to each pixel. More bits = more possible colours = larger file 1 bit = 2^1 = 2 colours 2 bits=2^2 = 4 colours 3 bits = 2^3 = 8 colours etc.
How is sound sampled and stored in digital form Measurements of amplitude (height of sound wave) taken at regular intervals and stored in binary. Each of these is known as a sample. Frequency of interval = sample rate. Bit depth = sample size
Name and define some key sound terms Sampling rate or sampling frequency - the number of samples per second Sample size (or bit depth) - the number of bits available for each sample Bit rate - the number of bits per second of audio = sampling frequency x sample size REMEMBER! A sample is a measurement of the height/amplitude of the analogue wave
What is bit rate? Bit rate is the number of bits per second of audio. Bit rate = Sample rate multiplied by bit depth.
What is Bit depth? The number of bits used to store each sample. The higher the number the better the quality. The higher the number the larger the file size.
If a sound file is 10 seconds long. It has a bit depth of 8 and a sample rate of 1GHz (1,000,000,000) What is the size of the file? Bit rate = Sample rate multiplied by bit depth. File size =Sample rate x bit depth x duration =1000,000,000 x 8 x 10 =80,000,000,000
How does sampling rate affect the size of the file? A higher sampling rate results in better sound quality but increases the size of the file requires more storage as more samples need to be stored. However the sound is closer to the original analogue wave.
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