AQA · GCSE · Computer Science
Course version: 8525 · Version from Sept 2020
Understand what a pixel is and be able to describe how pixels relate to an…
Full specification wording
Representing images: Understand what a pixel is and be able to describe how pixels relate to an image and the way images are displayed.
A pixel is one small square of colour in a bitmap image, and it is the smallest unit the image is built from.
Checked against the AQA 8525 specification (opens in a new tab) on .
- Point 1 of 18
Study notes
From the checked teaching notes for this specification point.
The idea
A pixel is one small square of colour in a bitmap image, and it is the smallest unit the image is built from. An image is stored as a grid of pixels: the width and height are counted in pixels, so a 1920 × 1080 image has 1920 pixels across and 1080 down. Each pixel holds a binary code describing its colour, and the number of bits per pixel (colour depth) controls how many different colours are possible. To display the image, the computer reads each pixel's code and lights the corresponding point on the screen; the screen's resolution decides how many pixels it can show. More pixels across the same physical area means a sharper, more detailed picture, but also a larger file because more codes must be stored.
What earns the marks
- A pixel is a single point (smallest element) in an image, and the term is short for picture element.
- An image is made up of a grid of pixels, with image dimensions given as a number of pixels wide by a number of pixels high.
- Each pixel is represented by a binary code that gives its colour, and colour depth is the number of bits used per pixel.
- When an image is displayed, the computer uses each pixel's stored code to set the colour of the corresponding point on the screen.
- Increasing the number of pixels (resolution) gives more detail but increases file size because more pixel codes must be stored.
Common mistakes and how to put them right
Thinking a pixel is a unit of file size rather than a single point of colour in an image.
Put it right by linking pixel to position and colour, not to storage.
Assuming more pixels always means a better display regardless of screen resolution.
Put it right by noting the screen can only show as many pixels as its resolution allows.
Believing each pixel stores a full colour name as text.
Put it right by explaining that each pixel's colour is held as a binary code.
Exam tips
- Learn the definition precisely: pixel = picture element, a single point in an image.
- When asked about file size, link it to the number of pixels multiplied by the bits per pixel.
- Use a concrete example such as a 1920 × 1080 image to show you understand width and height in pixels.
Try the lesson
The start of the Representing images: Understand what a pixel is and be able to describe how pixels relate to an image and the way images are displayed. lesson, made from checked teaching notes for this specification point.
Have a go first
An image on a screen is made up of many tiny individual coloured squares. What is each of these squares called?
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