Bitmap file size calculation
Lesson details
Learning outcome
I can explain how resolution and colour depth affect the file size of an image.
Key learning points
- The file size of a bitmap is determined from its colour depth and resolution.
- Increasing the colour depth of an image will increase its file size.
- Increasing the resoultion of an image will increase its file size.
- Selection of image resolution and colour depth depend on the use of the image and limitations imposed by the file size.
Keywords
Trade-off - accepting a limitation to achieve a beneficial outcome
Common misconception
Using a low resoultion or colour depth for an image makes it unusable.
A low resolution or colour depth does not necessarily make an image unusable. It depends on the purpose. Lower settings can be suitable for web use, icons or thumbnails, while higher quality is needed for printing or detailed graphics.
Teacher tip
Draw from pupils' examples of where they have seen poor quality digital images or delays in loading images on digital devices due to large file sizes. Ask pupils to articulate effects on their opinions of the image or the source providing the image.
Licence
Lesson video
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Prior knowledge starter quiz
6 Questions
Q1.What is the basic unit of data in a computer system?
Q2.What does a character set do?
Q3.Which character encoding system uses up to 32 bits per character?
Q4.Match the terms to their definitions:
smallest element of an image
number of bits used per pixel
total number of pixels in an image
a group of 8 bits
Q5.How many states are possible with a sequence of 4 bits?
Q6.What does colour depth quantify?
Assessment exit quiz
6 Questions
Q1.Place the following file sizes in order from smallest to largest:
Q2.What determines the file size of a bitmap image?
Q3.Match the terms to their definitions:
accepting a limitation to achieve a beneficial outcome
total number of pixels in an image
number of bits used per pixel
suitable for web use or thumbnails
suitable for printing or detailed graphics
Q4.What happens when the colour depth of an image is increased?
Q5.What is the effect of increasing the resolution of an image?
Q6.Which of the following is a trade-off when reducing image resolution?
To help you plan your 10 computer science lesson on: Bitmap file size calculation, download all teaching resources for free and adapt to suit your pupils' needs...
To help you plan your 10 computer science lesson on: Bitmap file size calculation, 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 4 computer science lessons from the Representation of text, images and sound unit, dive into the full secondary computer science curriculum, or learn more about lesson planning.