3.3 Flashcards
What are the different units for bytes?(5)
Kilo, 1kB is 1,000 bytes.
Mega, 1 MB is 1,000 kB
Giga, 1 GB is 1,000 MB
Terra, 1 TB is 1,000 GB
Peta, 1 PT is 1,000 TB
What are some uses of hexadecimal?(2)
Hexadecimal numbers are expressed more compactly than binary numbers and are much easier to understand and remember.
Therefore they are often used in picking colours for a graphic, instead of binary.
How many different values does ASCII and extended ASCII have?
ASCII has 128 different values while extended ASCII uses 8 bits rather than 7, and therefore has 256 unique characters.
What is the advantage of Unicode over ASCII?
Unicode has many more unique characters than ASCII because of the larger number of bits available to store a character code, therefore it allows for multilingual text in any language.
What is a pixel?
A pixel(picture element) is a single point in an image which can have its colour set independently.
Describe the different features of a bitmap image?(3)
The size of the image is expressed directly as the width in pixels by the height in pixels, e.g 600 x 400. Increasing the size of the image will increase the number of pixels to be stored and therefore increase the image file.
The number of bits used to store each pixel dictates how many colours an image can contain.
For example, an image using 4 colours will require 2 bits to record the colour of each pixel(4 different values in 2 bits).
What is colour depth?
The number of bits per pixel is known as colour depth. If the colour depth is increased, more bits are used to represent each pixel and the overall size of the file will increase.
What is pixel density?
Pixel density is measured in pixels per inch(PPI) and is used to describe the resolution of a computer screen, camera, or scanner.
How do you calculate the file size of an image?
Size in bits = image width x image height x colour depth.
To find this in bytes, just divide the final answer by 8.
Why do sound waves have to be converted to be stored on a computer?(2)
Sound waves are analogue, but anything stored on a computer has to be stored in a digital formate as a series of binary numbers.
To device used to convert real-world analogue signals into digital representation is an Analogue-to-Digital Converter or ADC.
Define sample.
A sample is a measure of amplitude at a specific point in time. A sound wave will be stored on a computer as a group of samples across a period of time.
Define sample rate and sample resolution.(4)
Sample resolution is the number of bits used to store each sample.
The more bits used, the greater variety of values that the amplitude can be and therefore a more accurate representation; it also increases the range in frequency’s.
Sample rate is the frequency at which the amplitude is recorded. This is usually measured in hertz, where 1 hertz = 1 sample per second.
The more frequently the sound is sampled, the better the quality and smoother the playback will sound
How do you calculate the size of a sound file?
Sample rate x sample resolution x number of seconds.
Why do we use data compression?(2)
One way of speeding up the rate at which files can be transmitted across the Internet is to compress them to make them smaller.
Therefore we compress files, to allow them to be transmitted quicker, take up less storage space, and allow large files to be sent via email attachment.
What is Lossy Compression?(2)
Lossy compression is a data encoding method(or algorithm) where files are compressed by removing some of the detail. For example, photographs can be stored using less colours and so less bits are needed per pixel. This is used in images, audio files and video files.
