Summary
Summary AQA A-Level Computer Science Revision Notes
- Institution
- AQA
Summarised revision notes of the specification topics, helping students achieve top grades in exams.
[Show more]
Seller
Follow
Content preview
CompressionWhat are the benefits of compression?
The amount of space required to store informations is reduced, meaning that
more files can be stored on a computer system or on external storage
The amount if data required to transmit data is reduced, meaning that less
bandwidth is used and this will reduce congestion and increase transmission
speed
Using compressed images on webpages reduces load times
Due to its reduced size, compressing video and audio streams improves
playback with less buffering/stuttering
Multiple files can be compressed into a single archive, simplifying their storage
and exchange
Lossy and Lossless Compression
What is lossy compression?
Unnecessary detail is permanently removed from the original data
This results in a permanent loss of quality but also the greatest reduction in file
size
Ideal for compressing images and audio, especially for transmission over the
Internet
Used for MP3, JPG and MP4
What is lossless compression?
Uses algorithms to efficiently represent repeating patterns within the original
data
No original data is lost, making it possible to perfectly restore the original data
Less reduction in file size than lossy compression but the only option where
data cannot be lost
Compression 1
, Used for compressing text, program files and other binary data
Used for TXT, EXE and HTML
Compression in Images
What types of compression works on images?
Images can be compressed using both lossy and lossless compression methods;
the method chosen depends on the type and purpose of the image being
compressed
What do JPEG images use?
The JPEG image format compresses files through the use of lossy compression by
permanently removing detail by ‘averaging’ similar colours across adjacent pixels,
JPEG is suitable for photographs but not images that contain ‘crisp’ details such as
text as the ‘averaging’ results in a ‘smudgy’ appearance on sharp edges.
What do PNG images use?
The PNG format, however, uses lossless compression by efficiently encoding
repeating patterns in the image to compress it; this results in higher quality images,
particularly for those that include sharp edges such as logos, icons and text, but
also results in larger files.
Run Length Encoding
What is it?
RLE is a simple form of lossless compression that represents repeating patterns of
data more efficiently
Compressing Audio
Why do we usually compress audio?
Digital audio files are relatively large, in order to store thousands on a computer or
phone or to stream audio over a 4G connection, compression is used
What format do we usually use?
MP3 is a very common audio compression format as it reduces the size of an audio
file without reducing the quality significantly by removing detail from an audio
Compression 2
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller r3njj. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for £4.49. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
60904 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy revision notes and other study material for 14 years now
