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Computer Science > Unit 3 > Flashcards

Unit 3 Flashcards

1
Q

Binary number system

A
  • Computers use a binary number system consisting of only 0s and 1s
  • Everything that a computer needs to process must be converted into binary format
  • This format is used for storing numbers, text, images, sound and program instructions
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2
Q

Bitmap image file formats

A
  • BMP
  • JPG
  • GIF
  • PNG
  • TIFF
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3
Q

What is sample resolution in terms of an image?

A

The number of bits per pixel

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4
Q

What is sample resolution in terms of a sound file?

A

The number of bits per sample

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5
Q

What is the typical screen resolution?

A

72 PPI (Pixels Per Inch)

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6
Q

Increasing the number of colours

A

More bits per pixel = more colour combinations
- 1 bit = 2 colours
- 2 bits = 4 colours
- 3 bits = 8 colours
- 4 bits = 16 colours

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7
Q

What is the relationship between colour and bit depth?

A
  • Each pixel can represent a finite number of colours
  • A pixel is attributed a number of n bits
  • The number of combinations (2^n) dictates the bit depth and therefore the number of colours that can be represented
  • A higher bit depth gives a greater range of colour and a better quality of image
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8
Q

How does the number of colours affect the file size?

A

An increase in the number of colours that are used in an image (the bit depth) will increase the file size

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9
Q

How does the size of the image affect file size?

A
  • Size has two meanings
  • An increase in the number of pixels in the image will increase the file size
  • If an images physical size is increased by making each pixel larger than there is no change in the file size
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10
Q

Difference between analogue and digital sound signals

A
  • Analogue sound signals are continuous
  • Digital signals are discrete, this means the sound wave is sampled at regular intervals
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11
Q

how is sound converted into digital form (what is used to convert the sound waves)?

A
  • Sounds must be converted into a digital from in order to be stored and processed by a computer
  • An Analogue to Digital Converter (ADC) is used to convert inputs to digital signals
  • A Digital to Audio Converter (DAC) is used to convert digital signals to outputs

ADC –> Processing –> DAC

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12
Q

What is a sound sample?

A

A measurement of amplitude of a sound wave at a given time

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13
Q

Sound sampling

A
  • Sound is sampled using a sample resolution (bit depth) and sampling rate
  • The sample resolution determines how closely the wave is sampled on the y-axis
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14
Q

What is the sampling rate?

A
  • The sampling rate is the number of samples taken per second. It is measured in hertz (Hz)
  • The frequency or sample rate per second affects the level of detail in the digital representation
  • The greater the frequency, the greater the accuracy and file size
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15
Q

What is the sample resolution?

A
  • The number of bits used to record each measurement
  • More bits used per sample enables the height of the wave to be more accurately measured but increases the file size
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16
Q

Lossless compression

A

Lossless compression formats are able to reduce the file size when compressed but not lose any information

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17
Q

Examples of lossless music file formats

A
  • FLAC (Free Lossless Audio Codec)
  • ALAC (Apple Lossless Audio Codec)
  • WMA Lossless (Widows Media Audio)
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18
Q

Lossy compression

A
  • Lossy compression removes sounds that we can’t easily hear or that least affect the perceived playback quality
  • Lossy compression leaves out some data from the original so can negatively affect the sound quality
  • Useful for storing, downloading or streaming
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19
Q

What is the formula for calculating the size of an uncompressed music file?

A

sampling rate x bit depth x duration

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20
Q

Examples of lossy file formats

A
  • MP3
  • AAC (Advanced Audio Coding)
21
Q

What is compression?

A

Reducing the size of a file

22
Q

Why is compression software used?

A

Reduces the size of a file so it takes up less disk space, and is quicker to download over the Internet

23
Q

How many bits are in a byte?

A

8 bits = 1 byte

24
Q

How many bits does ASCII use to store each character?

A

7 bits

25
Q

How many characters can ASCII encode?

A

ASCII encodes 128 characters

26
Q

Advantages of using Unicode instead of ASCII

A
  • Can represent a wider range of characters
  • Can represent characters from a wider range of languages
27
Q

What is the result of a binary shift to the left?

A

Doubles the original number

28
Q

What is the result of a binary shift to the right?

A

Halves the original number

29
Q

What is a pixel?

A

Short for picture element, is a single point in an image

30
Q

What is the colour depth of an image?

A

The number of bits used to represent each pixel

31
Q

How do you calculate a bitmap image file size (in bits)?

A

size = width x height x colour bit depth

32
Q

How do you calculate bitmap image file size (in bytes)?

A

size = width x height x colour bit depth / 8

33
Q

What is meant by sampling rate?

A

The number of samples taken in a second, and is measure in Hertz

34
Q

How do you calculate the size of a sound file (in bytes)?

A

size = sampling rate x sampling resolution x duration / 8

35
Q

What is image resolution?

A
  • Refers to the clarity of an image as it appears on a screen or on paper
  • Can be expressed as the number of pixels that an image contains per inch
36
Q

Describe the affect of colour depth on the file size

A
  • When colour depth is increased, the file size increases also
  • The more bits that are used to to represent colours, the larger the storage space required to save the image
37
Q

Describe how analogue sound waves are converted into digital sound

A
  • Analogue sound is received by a microphone
  • This is converted into an electrical analogue signal
  • The signal amplitude is measured at regular intervals
  • The values are rounded to a level (quantisation)
  • The values are stored as a series of binary numbers
38
Q

Sound waves are analogue, what does this mean?

A

Continuously changing

39
Q

Why is file compression used?

A
  • To reduce the amount of storage needed on a computer to save files
  • Allow large files to be transmitted as an email attachment
  • Allow a file to be transmitted in less time
40
Q

What is lossy compression?

A

A data encoding method where files are compressed by removing some of the detail

41
Q

When is lossy compression used?

A

To compress images, audio files and video files

42
Q

What is lossless compression?

A

A data encoding method where files are compressed but no data is lost

43
Q

When is lossless compression used?

A

To compress data and text files

44
Q

What is run length encoding?

A

RLE is a simple form of lossless data compression in which runs of data are stored using frequency/data pairs

45
Q

When is RLE not useful?

A

RLE is not so useful with files that don’t have many runs, and in fact increase the file size

46
Q

When is RLE most useful?

A

On simple images such as icons that contain many pixels that are the same colour

47
Q

What is Huffman coding?

A
  • A compression technique used to reduce the number of bits used to represent each letter
  • The more frequently a letter appears in the text, the fewer bits are used to represent it in a text file
48
Q

State two reasons why data are compressed

A
  • To reduce file size
  • To reduce downloading time, typically used for streaming

Computer Science (9 decks)

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