KS3 Data and data representation
How does a computer store an image? What happens if we decrease the quality of an image file? Can we recreate the original image if we decrease its' quality? Are there ways to reduce the size of an audio file without losing the quality of the audio when it is played back?
Understanding data and how it is represented within the computer system can help students become better programmers and better able to understand the limitations of the data processing. Knowing that no matter how much an image is enhanced no extra details can be added, or that if an audio track is down sampled data is going to be lost are both fundamental to understanding.
Links and Resources
A lesson plan and series of activities to help students understand that bitmapped images are built up purely of pixels. This includes a spreadsheet designed to represent monochrome and then simple colour images. The effect of increasing the range of colours available and its' effect on file size is discussed in some depth.
Although this resource does not contain any instructions for how to use it in a lesson, or lesson plans to go with it, it could easily be used to support the delivery of other activities as students learn about how images are created and stored, as well as how they are represented in the memory of a computer. Asking students to experiment with the images they are able to generate using this tool should give them a firmer grasp of how pixel data can be encoded in an image file
A series of spreadsheet-based activities to simulate both binary and hexadecimal encoded image files. The students are required to convert between binary and hexadecimal as well as too and from denary as part of the process of solving these puzzles. The worksheet contains a number of example pictures which the students are required to recreate. There are a number of revised spreadsheet files each with slightly modified versions to enable different variants of the basic process to be undertaken by the students.
A resource from CS Unplugged which looks at ways in which images can be represented by black and white pixels. It includes a number of activities to help students look at the way in which Run Length Encoding can be used to minimise the actual size of data which has to be transmitted by a fax machine (or stored on a disk). A discussion of the underlying ideas is included.
A highly technical overview of how sound is represented in a computer, how digitising sound changes the quality of it and how reducing the sample rates can effect the resulting audio. The resource also comes with a number of sound samples to illustrate these concepts, along with both Python and Scratch programs to enable students to investigate further
This resource consists of a presentation which looks in various ways at how digital images and sounds are quantified in such a way that the computer can store and interpret them. This looks at the effects of digitising different types of data, and the effect that this has on both the size and the quality of the resulting files. It may be necessary to produce some supporting activities for students to undertake in lessons, to support their understanding of the content of this presentation.
An introduction to the binary number system, this activity from CS Unplugged explains the theories which underpin the use of base 2, as well as why and how computers use this as their fundamental building block. A series of activities are included to help consolidate students understanding of the binary system, and include discussion of how characters and other types of data can be encoded.
An unplugged activity to convert binary numbers into coordinates that enable students to recreate an image using values given in binary. The resource also includes a spreadsheet which can be used to make more complex images for use with students at a more advanced level. The presentation is more of a discussion of computational thinking and is not really relevant to this activity. Once students have completed the activity for themselves, they could be asked to create their own image in a similar way to the one they have recreated, and generate a coordinate list for their image in binary. The discussions listed in the activity sheet should also be useful to broaden students understanding of the use of binary as well as how it might be possible to speed up a computer system in similar situations.
Reducing the amount of space that information occupies in a computer memory can make it easier to store more data, this activity from CS Unplugged looks at how text can be compressed so that no information is lost, but the overall file size can be significantly reduced. A series of activities to consolidate these ideas are presented along with an in depth discussion of what is going on in terms of the underlying computer science.