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A-level Computer Science > SLR 12 - coding texts and graphics > Flashcards

SLR 12 - coding texts and graphics Flashcards

1
Q

What is character code?

A

a decimal digit to represent a character

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2
Q

What does ASCII stand for?

A

American Standard Code for Information Interchange

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3
Q

What are the two most widely used information coding systems?

A
  • ASCII
  • Unicode
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4
Q

How did ASCII develop over time?

A
  • originally had 7 bits (128 different characters)
  • created extended ASCII = 8 bit (256 characters)
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5
Q

What was Unicode?

A

character set that can represent the widest variety of alphabets and symbols universally, using 8 to 48 bits per character

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6
Q

What happens when data is transmitted?

A

errors occur due to changes during transmission

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7
Q

What are the four different types of error checking?

A
  • parity bit
  • majority voting
  • checksums
  • check digits
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8
Q

How do parity bits work?

A
  • 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
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9
Q

What is the con of parity bits?

A
  • if one or more bits are wrong the parity bit is ineffective
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10
Q

What is majority voting?

A
  • each bit gets sent three times
  • whichever number occurs most times for each bit is taken as the correct value
  • erroneous data is ignored
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11
Q

What are the cons of majority voting?

A
  • 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
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12
Q

What is a checksum?

A
  • you add up the sum of the binary numbers
  • if the sum = the value transmitted then it is correct
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13
Q

What are the cons of a checksum?

A

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

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14
Q

What is a check digit?

A
  • 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
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15
Q

How many bits does an RGB colour pallet use?

A

24 bits

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16
Q

How do bitmapped images work?

A
  • images are broken into pixels
  • each pixel is assigned a binary value
  • the value assigned to a pixel determines it colour
17
Q

What is image resolution?

A
  • 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
18
Q

What is the calculation for the number of different pixels that can be represented?

A

2^n

19
Q

What are vector images?

A
  • 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
20
Q

What are the pros of a vector image?

A
  • 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
21
Q

Pros of bitmap images?

A
  • Used for storing photographs
  • Often use more storage space than vector graphics
22
Q

How do computers represent sound?

A

as a sequence of samples, each taking a discrete digital value

23
Q

What is a sampling rate and what is it measured in?

A

the number of samples per second (hertz)

24
Q

How do you calculate the file size of an image?

A

pixel length x pixel width x colour depth

25
Q

What is bitmap metadata?

A
  • data about data
  • it stored alongside bits which make up the image and increase the overall file size
26
Q

What are some examples of bitmap image metadata?

A
  • dimensions
  • colour depth
  • file depth
  • locations
  • creation date
  • last modified date
  • author
  • etc.
27
Q

What do you need to store about a vector image?

A
  • coordinates for the centre of the circle
  • radius
  • fill colour
  • outline colour
  • outline width
28
Q

What are vector graphics usually used for?

A

simple images like company logos
can’t be used for photographs

A-level Computer Science (11 decks)

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