Representing bitmap images
Lesson details
Learning outcome
I can describe how computers represent bitmap images.
Key learning points
- A pixel is the smallest element in an image.
- A bitmap image is one that is represented by a grid of pixels.
- The colour a pixel should display is described by a binary sequence.
- The colour depth of a bitmap image quantifies the number of bits used to represent each pixel.
- The resolution of an image describes the total pixels an image contains based on its width and height.
Keywords
Pixel - a single element of an image on a computer screen
Colour depth - the number of bits used to represent the colour of each pixel, which is also known as bit depth
Resolution - total amount of pixels an image contains based on its width and height expressed in pixels
Common misconception
Bitmap images that are large on screen are always poor quality.
The quality of a bitmap image depends on its resolution, not just its size on the screen. A high-resolution bitmap can appear sharp and detailed, while a low-resolution bitmap may look pixelated when enlarged.
Teacher tip
A bitmap image can be used to demonstrate changes caused by adapting its physical size. Pupils like to see images they are familiar with get stretched so they can begin to see the individual pixels that make up the image.
Licence
except where otherwise stated. See Oak's terms & conditions (Collection 2).Lesson video
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Prior knowledge starter quiz
6 Questions
Q1.What is a binary digit (bit)?
Q2.What is a group of 8 bits called?
Q3.What does a character set do?
Q4.Which character representation method uses 8 bits per character?
Q5.What is the method of character representation that uses up to 32 bits per character?
Q6.How many possible states are there in a sequence of 3 bits?
Assessment exit quiz
6 Questions
Q1.Which term refers to an image format that is composed of a grid of individual pixels, each with its own colour value?
Q2.What determines the quality of a bitmap image?
Q3.What is the smallest element of a bitmap image?
Q4.Why might a bitmap image look pixelated?
Q5.Which term describes the number of bits used to represent the colour of each pixel in an image?
Q6.Match the term to its definition:
Allows for 256 different colours.
Allows for 65,536 different colours.
Allows for 16.7 million different colours.
To help you plan your 10 computer science lesson on: Representing bitmap images, download all teaching resources for free and adapt to suit your pupils' needs...
To help you plan your 10 computer science lesson on: Representing bitmap 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 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.