File size of digital images
Lesson details
Learning outcome
I can describe how image file sizes are calculated and how changes to image quality and colour accuracy adjusts this.
Key learning points
- The colour of each element in a digital image is represented using binary digits.
- Changing image quality (resolution) affects file size: higher quality increases size, lower quality decreases it.
- Changing colour depth affects file size: higher colour accuracy increases size, lower accuracy decreases it.
Keywords
Resolution - total amount of pixels an image contains based on its width and height expressed in pixels
Colour depth - the number of bits used to represent the colour of each pixel, which is also known as bit depth
File size - a measure of how much binary data a file contains
Common misconception
1 bit is always used to represent 1 pixel.
While bits are used to represent the colour of pixels, it's not always a one-to-one relationship. The number of bits used can vary depending on the colour depth of the image.
Teacher tip
You can use a microscope to view and phone screen and see the individual pixels that make up the display.
Licence
Lesson video
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Prior knowledge starter quiz
6 Questions
Q1.What is a pixel?
Q2.How are digital images arranged?
Q3.What does RGB stand for in digital imaging?
Q4.What unit is used to measure data in a computer system?
Q5.Which is the smallest file size?
Q6.What can happen to an image if you make it bigger?
Assessment exit quiz
6 Questions
Q1.Match the term to its definition:
dimensions of an image in pixels
number of bits used to represent colour
amount of data a file contains
Q2.Match the concept to its effect:
enhances image clarity
decreases image clarity
enhances colour accuracy and richness
decreases colour accuracy and richness
Q3.What happens when you increase the colour depth of an image?
Q4.What does file size measure?
Q5.How can file size be reduced without changing resolution?
Q6.What is the file size of a file measuring 10 x 10 pixels and which allows 4 colours?
To help you plan your 9 computing lesson on: File size of digital images, download all teaching resources for free and adapt to suit your pupils' needs...
To help you plan your 9 computing lesson on: File size of digital images, download all teaching resources for free and adapt to suit your pupils' needs.
The starter quiz will activate and check your pupils' prior knowledge, with versions available both with and without answers in PDF format.
We use learning cycles to break down learning into key concepts or ideas linked to the learning outcome. Each learning cycle features explanations with checks for understanding and practice tasks with feedback. All of this is found in our slide decks, ready for you to download and edit. The practice tasks are also available as printable worksheets and some lessons have additional materials with extra material you might need for teaching the lesson.
The assessment exit quiz will test your pupils' understanding of the key learning points.
Our video is a tool for planning, showing how other teachers might teach the lesson, offering helpful tips, modelled explanations and inspiration for your own delivery in the classroom. Plus, you can set it as homework or revision for pupils and keep their learning on track by sharing an online pupil version of this lesson.
Explore more key stage 3 computing lessons from the Data representation: images and sound unit, dive into the full secondary computing curriculum, or learn more about lesson planning.