ALEX Classroom Resource

  

Coding - Compression

  Classroom Resource Information  

Title:

Coding - Compression

URL:

https://csfieldguide.org.nz/en/chapters/coding-compression/

Content Source:

Other
CS Field Guide
Type: Lesson/Unit Plan

Overview:

Data compression reduces the amount of space needed to store files. If you can halve the size of a file, you can store twice as many files for the same cost, or you can download the files twice as fast (and at half the cost if you're paying for the download). Even though disks are getting bigger and high bandwidth is becoming common, it's nice to get even more value by working with smaller, compressed files. For large data warehouses, like those kept by Google and Facebook, halving the amount of space taken can represent a massive reduction in the space and computing required, and consequently big savings in power consumption and cooling, and a huge reduction in the impact on the environment.

Common forms of compression that are currently in use include JPEG (used for photos), MP3 (used for audio), MPEG (used for videos including DVDs), and ZIP (for many kinds of data). For example, the JPEG method reduces photos to a tenth or smaller of their original size, which means that a camera can store 10 times as many photos, and images on the web can be downloaded 10 times faster.

So what's the catch? Well, there can be an issue with the quality of the data – for example, a highly compressed JPEG image doesn't look as sharp as an image that hasn't been compressed. Also, it takes processing time to compress and decompress the data. In most cases, the tradeoff is worth it, but not always.

Content Standard(s):
Digital Literacy and Computer Science
DLIT (2018)
Grade: 9-12
28) Develop a model that reflects the methods, procedures and concepts used by computing devices in translating digital bits as real-world phenomena, such as print characters, sound, images, and video.

Insight Unpacked Content
Evidence Of Student Attainment:
Students will:
  • develop a model that demonstrates a method used by computing devices to translate digital bits as real-world phenomena.
  • develop a model that demonstrates a procedure used by computing devices to translate digital bits as real-world phenomena.
  • develop a model that demonstrates a concept used by computing devices to translate digital bits as real-world phenomena.
Knowledge:
Students know:
  • computing devices use methods, procedures, and concepts to translate digital bits from an abstract form into real-world phenomena such as sound, images, etc.
  • each device has a process for translating from computational information to real-world phenomena.
Skills:
Students are able to:
  • model the translation of digital information to real-world phenomena.
  • understand that this process is that way in which computing devices and humans interact.
Understanding:
Students understand that:
  • for computing devices to communicate in a way in which humans understand, there is a process (methods, procedures, and concepts) used to translate computational information to real-world phenomena.
Digital Literacy and Computer Science
DLIT (2018)
Grade: 9-12
29) Summarize the role of compression and encryption in modifying the structure of digital artifacts and the varieties of information carried in the metadata of these artifacts.

Insight Unpacked Content
Evidence Of Student Attainment:
Students will:
  • summarize the roles of compression and encryption.
  • examine how the structure of digital artifacts may be modified when compressed or encrypted.
  • describe the effects on the metadata of an artifact when compressing or encrypting the file.
Teacher Vocabulary:
  • compression
  • encryption
  • metadata
Knowledge:
Students know:
  • that when a file is altered in any way, changes may be seen in the file metadata.
  • compression and encryption are two methods used when sharing data.
Skills:
Students are able to:
  • explain the roles of compression and encryption.
  • summarize the effects of compression and encryption on the metadata of a digital artifact.
Understanding:
Students understand that:
  • any process applied to data has the potential to alter the structure of the data.
  • it is important to be aware of potential changes to data structure when electing to use a process.
Tags: compression, decoding, encoding, Huffman tree, interpolation, JPEG, lossless compression, lossy compression, MP3
License Type: Attribution Non-Commercial Share Alike
For full descriptions of license types and a guide to usage, visit :
https://creativecommons.org/licenses
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Author: Aimee Bates