2.3.4 Data Compression Flashcards

1
Q

Data compression

A

Process used to reduce the storage requirements of a file.

Process used algorithms to look for repeating patterns that can be stored with less data.

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2
Q

Reasons to compress files

A
  • reduce amount of storage space needed for storage devices

- reduce bandwidth needed to upload/ download file.

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3
Q

Types of compressions

A

LOSSY

LOSSLESS

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4
Q

Lossy compression

A

Some original data will be lost during compression

Notice difference in quality.

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5
Q

Lossless

A

Algorithms are used but little/ no data lost.

Impossible to notice difference in quality.

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6
Q

Zipping

A

Procedure for compressing data files

Uses an algorithm called LZW

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7
Q

LZW - In zipping

A
  • looks for recurring patterns with data.
  • can be placed with a single character.
  • less bits are used to represent original data.
  • when zipped file decompressed by zipping software the reverse procedure happens.
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8
Q

WAV waveform audio file format

A
  • portable- played by most audio software.
  • uncompressed but can be used to store compressed sounds.
  • used by audio profession to record sounds.
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9
Q

Txt

A
  • only holds letters and numbers.
  • no formatting or images.
  • no compression as already small file.
  • May contain a special symbol to signify the end of file.
  • sometimes used to send basic data between larger applications.
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10
Q

Analogue and digital sounds.

A
  • humans hear in analogue- continuously varying signal.

- computers digital- need to convert sound to digital data.

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11
Q

Converting sound to digital data

A
  • audio captured via input device ie mic.
  • sound travels down wire as an electrical signal.
  • computer changes signal to binary data ADC
  • software saves the data as sound files with the quality being determined by sample rate and sample resolution.
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12
Q

BMP

A
  • map of all the bits
  • details of all the pixels that make up and image are stored.
  • each pixel has the digital representation of its individual colour stored separately.
  • colours that fade into other colours can be accurately represented.
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13
Q

JPEG

A
  • looks for sequences of pixels that repeat and only store data once.
  • used on webpages
  • supports 16million colours.
  • LOSSY compression but amount of detail lost can be varied by user.
  • not support transparency/ animation.
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14
Q

GIF

A
  • restricted to 8 bit colour depth 256 colours.
  • LOSSLESS compression when used on simple images with blocks of colour.
  • LOSSY compression for real or lifelike images.
  • small file sizes
  • can contain transparency pixels and supports animation.
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15
Q

MPEG

A
  • include MP3 audio and MPEG4 video
  • discards sounds that typical human air does not notice for music.
  • for video 24/25 FPS- full frames only stored occasionally- only store data different to previous frame.
  • heavily compresses the source by only storing data about non changing pixels once.
  • designed for online streaming.
  • LOSSY compression but can maintain v high image quality.
  • can contain subtitles
  • default format used by mobile phones and digital cameras.
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16
Q

AVI audio video interleave

A
  • portable and be played by most video software
  • Does not compress video and therefore keeps full quality.
  • can contain multiple streams
  • multiple camera angles
  • v high file sizes.