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Compression - Coggle Diagram
Compression
Lossless compression
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It works by identifying patterns in the information and restructuring how the data is stored - there is no effect on the quality of the information.
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text file - create a list of all the characters and the binary codes that represent them - then record where and how many times each character is used
image file - create an list of all the pixel colours and the binary codes that represent them - then record where and how many times each pixel colour is used
audio file - make a note of the binary codes that represent silence - then record where each period of silence occurs and how long it lasts for
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The binary codes that record location and frequency will be considerably shorter than if you had to record the codes for every single occurrence of silence/character/pixel.
How compression works
Original (uncompressed) data files are called RAW files (not an acronym - just means that the file has not been altered in any way)
Compression works by detecting patterns in the RAW file’s information. This is true of text, image, video or music files.
A pattern means that some of the data is identical, but is just located in different places in the file.
Compression works by analysing the patterns in the information and making changes to to the data. This can involve:
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Lossy compression
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It works by identifying patterns in the information and deciding how much data it can throw away without noticeably affecting the quality of the information.
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audio files - reduce sample frequency (no. of samples taken per second), bit depth (bits per sample) or no. of channels (e.g. stereo [2 channels] to mono [1 channel]) - all of these changes reduce the bit rate (no. of bits processed per second)
compression
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Compression means to reduce the size of a data file whilst still retaining most, or even all, of the original information.
Commonly used file types that can be compressed are documents, music files, video and image files.
Compression may change various attributes of a file. These attributes include: file type, resolution, dimensions, metadata, bit depth, sample frequency, number of channels
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Compression ratios
efficiency of video and sound compression:
compression ratio = original data rate/compressed data rate
efficiency of text and image compression:
compression ratio = Original data size/compressed data size
the higher the ratio, the more efficient the compression
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data
In terms of data storage, data is the bits (1s and 0s) used to store a file - it has no meaning for the user.
Information
Original (uncompressed) data files are called RAW files (not an acronym - just means that the file has not been altered in any way)