Teach Computing

Revision notes, activities, lesson plans, teaching ideas, and other resources for GCSE, A-Level, and IB Computer Science teachers and students.

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Resources discount offer

Representing images, sound and other data

Click here for recommended AQA A-Level Computer Science textbooks.

4.5.6.1 Bit patterns, images, sound and other data

4.5.6.2 Analogue and digital

4.5.6.3 Analogue/digital conversion

4.5.6.4 Bitmapped graphics

Bitmap lesson plan

Bitmaps Activity

These activities involve students converting between bitmap images and numeric representations of them in binary and hexadecimal. This is a great way to see how relatively complex information can still be represented as binary. You can download the worksheet with guidance and an additional blank worksheet.

The activities were created by Gary Kacmarcik at the Computer Science & Engineering for K-12 site, which contains an excellent range of activities. They are licensed under the Creative Commons Attribution-Share Alike 3.0 Unported License.


Updated: 2015-04-15
Image representation

Image Representation - Flash activity

This Flash activity lets students draw a simple bitmap image and represents it using a simple run-length encoding (RLE) algorithm in real time. Students can also important text representations of the compressed data and the application will draw the corresponding image. The web page is not in English but the application is still perfectly usable.


Updated: 2015-04-15
Hexadecimal colour codes

Hexadecimal colour codes

Section 5.5.2 of this much bigger page on data representation covers the uses of hexadecimal numbers to represent colours in images. It explains the correlation between the hexadecimal digits and the number of bits available, and the effect the bit depth has on the appearance of the image. The excellent interactives really make the concept come alive and visually highlight these differences to students. A highly recommended resource.


Updated: 2015-06-03

4.5.6.5 Vector graphics

4.5.6.6 Vector graphics versus bitmapped graphics

4.5.6.7 Digital representation of sound

4.5.6.8 Musical Instrument Digital Interface (MIDI)

4.5.6.9 Data compression

Image, audio, and text compression

Image, audio, and text compression

This very comprehensive page from the Computer Science Field Guide has extensive but clear notes on lossless and lossy compression. The page is well written and designed for a high school audience, with easy to understand examples, video, and even interactive sections. There are also extension "Extra for Experts" sections. The page covers image compression, audio compression, and text compression.


Updated: 2015-04-16
Text and image compression

Compression

A short Computerphile video which explains basic compression techniques and how they can be applied to text files and image files. The video also addresses the differences between lossy and lossless compression.


Updated: 2015-05-27
Compression

Compression: Crash Course Computer Science

This video explains compression techniques in the context of images. It is recommended that students have an understanding of how image data is stored (e.g. bit depths) before watching this video. The video is very comprehensive and so it may take a couple of viewings to fully understand the details of the examples being presented, but it is worth it.


Updated: 2018-02-17
Compression

Lossy and Lossless (RLE) Compression

These videos from Computer Science Tutor make great revision sources. This particular videos covers the theory behind the two types of compression - lossless and lossy.


Updated: 2018-02-17

4.5.6.10 Encryption

Encryption techniques

Encryption (National Codes Centre)

The National Codes Centre at Bletchley Park (who know a thing or two about ciphers) have comprehensive lesson plans, teacher's notes, and student activities for various types of encryption, from simple substitution ciphers (Caesar ciphers) through the infamous Enigma and Lorenz ciphers to modern day methods.


Updated: 2015-04-16
Encryption

Encryption

Very detailed but clear explanations of the various types of encryption systems, from simple substitution ciphers (Caesar ciphers) to modern public key encryption systems. The page also explains the types of attacks that can be performed against ciphers, such as known plaintext attacks and frequency analysis attacks. A variety of interactive applets held improve understanding.


Updated: 2015-04-19
Encryption systems

Braingle: Codes, Ciphers, Encryption and Cryptography

Braingle contains extensive notes on many different types of cipher systems from Caesar ciphers to four-square ciphers. There are dozens of examples and some interactives to help students understand the different ways plaintext can be encrypted. This could be a good site to support a lesson starter activity or extension activities for more advanced students who are interested in encryption systems.


Updated: 2015-04-25
Encryption

Encryption and Caesar Cipher

An overview of the encryption process, from plain text to cipher text, along with a clear explanation of the Caesar cipher algorithm (which is sufficient for most GCSE Computer Science courses). A good revision resource.


Updated: 2018-02-17