paper 1 - data representation and compression Flashcards
what are alphanumeric characters used for?
they are used to make words and strings. They include uppercase and lowercase letters, the digits 1-9, and symbols like ? + and £
what are character sets?
collections of characters that a computer recognises from their binary representation
what is ASCII?
- ASCII is the most commonly-used character set in the English-speaking world. Each ASCII character is given a 7-bit binary code - this means it can represent a total of 128 different characters, including all the letters in the English alphabet, numbers, symbols and commands
- An extra bit (0) is added to the start of the binary code for each ASCII character. This means each ASCII character fits nicely into 1 byte
what is extended ASCII?
a character set which gives each character an 8-bit binary code, allowing for 256 characters to be represented. The first 128 characters are in exactly the same order as the ASCII characters.
Extended ASCII is particularly useful for many European languages like French and German which include accents on some of the vowels
what is unicode?
- unicode is a character set that comes in several different forms and tries to cover every possible character that might be written. In its most common forms it uses 16-bit and 32-bit binary codes
- Unicode is that covers all major languages , even those that use a completely different alphabet like Greek, Russian and Chinese
what are the 2 types of images?
bitmap and vector
what are bitmap images mainly used for?
photos
how are bitmap images stored as binary?
Bitmap images are made up of lots of tiny dots, called pixels. The colour of each pixel is represented by a binary code. The number or colours available in an image is related to the number of bits the code has
what is colour depth?
the number of bits used for each pixel
what is the formula to work out how many colours can be made in an image?
total number of colours = 2^n (where n = number of bits per pixel, or bpp)
what colour depth do most devices use?
a 24-bit colour depth, with 8 bits used to indicate the levels of red, green and blue needed for each pixel. It is estimated that the human eye can see around 10 million different colours, so a 24-bit colour depth should cover every colour that you could possibly see
what is the resolution of an image? What is resolution normally measured in?
the density of pixels in an image, i.e. how many pixels are within a certain area. It’s normally measured in dots per inch (dpi)
what does increasing the resolution or the colour depth of an image mean?
that there are more bits in the image. This improves the image quality but also increases the file size
what is metadata? (images)
the information stored in an image file which helps the computer recreate the image on the screen from the binary data in each pixel. It usually includes the image’s file format, height, width, colour depth and resolution. It can also include extra information, like the time and date that the image was created or last edited. Without metadata, devices would not be able to display the image on screen as intended
what are the steps to sampling sound and storing it digitally?
- sound is recorded by a microphone as an analogue signal. Analogue signals are pieces of continually changing data
- analogue signals need to be converted into digital data so that computers can read and store sound files. This is done by analogue to digital converters, which are found in most modern recording devices
- the process of converting analogue to digital is called sampling: to convert the analogue recording to digital data, we sample the amplitude of the wave at regular intervals. The amplitude can only take certain values depending on the bit rate.
- once the device has sampled the recording, it creates the curve digitally
