SLR 12 - coding texts and graphics Flashcards
What is character code?
a decimal digit to represent a character
What does ASCII stand for?
American Standard Code for Information Interchange
What are the two most widely used information coding systems?
- ASCII
- Unicode
How did ASCII develop over time?
- originally had 7 bits (128 different characters)
- created extended ASCII = 8 bit (256 characters)
What was Unicode?
character set that can represent the widest variety of alphabets and symbols universally, using 8 to 48 bits per character
What happens when data is transmitted?
errors occur due to changes during transmission
What are the four different types of error checking?
- parity bit
- majority voting
- checksums
- check digits
How do parity bits work?
- at the start of the byte you send a parity bit
- this makes the total number or bits in the binary number odd (odd number of ones) or even (even number of ones)
- if after transmission the total number of ones is even but you stated the parity was odd you know there has been an error in transmission
What is the con of parity bits?
- if one or more bits are wrong the parity bit is ineffective
What is majority voting?
- each bit gets sent three times
- whichever number occurs most times for each bit is taken as the correct value
- erroneous data is ignored
What are the cons of majority voting?
- There could be an instant where the data is wrong three times
- Also its no the best as you have to send the data three times so more storage
What is a checksum?
- you add up the sum of the binary numbers
- if the sum = the value transmitted then it is correct
What are the cons of a checksum?
if two pieces or multiple pieces of data change but they still add up to the checksum, it might be wrong but you don’t realise
What is a check digit?
- Most commonly in barcodes
- Normally referred to with ISBN, when you give a device a very long number - ISBN number multiplied by weight
- Add all the values
- Divide the value by 10
- Take the remainder away from 10 and that is your check digit
How many bits does an RGB colour pallet use?
24 bits
How do bitmapped images work?
- images are broken into pixels
- each pixel is assigned a binary value
- the value assigned to a pixel determines it colour
What is image resolution?
- the number of dots per square inch, where a dot is a pixel
- resolution can also refer to the number of pixels in an image
What is the calculation for the number of different pixels that can be represented?
2^n
What are vector images?
- geometric objects and shapes are used to create images
- properties for each geometric shape or object in the image are stored within a drawing list
What are the pros of a vector image?
- Can be scaled without losing quality
- Well suited to simple images which use shapes but no good for photograph
- Frequently use less storage space than bitmapped graphics
Pros of bitmap images?
- Used for storing photographs
- Often use more storage space than vector graphics
How do computers represent sound?
as a sequence of samples, each taking a discrete digital value
What is a sampling rate and what is it measured in?
the number of samples per second (hertz)
How do you calculate the file size of an image?
pixel length x pixel width x colour depth
What is bitmap metadata?
- data about data
- it stored alongside bits which make up the image and increase the overall file size
What are some examples of bitmap image metadata?
- dimensions
- colour depth
- file depth
- locations
- creation date
- last modified date
- author
- etc.
What do you need to store about a vector image?
- coordinates for the centre of the circle
- radius
- fill colour
- outline colour
- outline width
What are vector graphics usually used for?
simple images like company logos
can’t be used for photographs
