--- title: "Bitmap Images: Pixels, Resolution and Colour Depth" description: "A picture stored as a grid of pixels, each one a binary colour value. Resolution and colour depth decide both how it looks and how big the file is." canonical: https://lightmysky.com/learn/computing/bitmap-images-pixels-resolution-and-colour-depth-mt_-Tr40QK8sN source: https://lightmysky.com/learn/computing/bitmap-images-pixels-resolution-and-colour-depth-mt_-Tr40QK8sN.md retrieved: 2026-11-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Bitmap Images: Pixels, Resolution and Colour Depth A picture stored as a grid of pixels, each one a binary colour value. Resolution and colour depth decide both how it looks and how big the file is. Subject: Computing · Area: Computer Systems · Ages 14 to 16 Page: https://lightmysky.com/learn/computing/bitmap-images-pixels-resolution-and-colour-depth-mt_-Tr40QK8sN ## Ready when they can - Explain what resolution controls and what colour depth controls - Work out the size of an uncompressed image from its dimensions and colour depth - Predict what happens to a picture blown up past its resolution ## Lesson: Pictures made of tiny squares A digital picture is a grid of pixels. Each pixel is one small square with a stored colour value. In a two-colour bitmap, one bit can mark one colour as 0 and the other as 1. **Example.** For an uncompressed image, multiply width by height by colour depth. An 80 by 50 image with 4 bits per pixel takes 80 times 50 times 4, or 16,000 bits. Doubling the depth to 8 bits doubles the bit count. **Example.** A 16 by 16 two-colour icon has 256 pixels. With one bit per pixel, its uncompressed data takes 256 bits. **Example.** A 30 by 20 image uses 2 bits per pixel. It has 600 pixels, so it takes 1,200 bits before compression. Resolution describes the pixel dimensions of an image, such as 100 by 100. More pixels packed into the same space can show finer detail. Colour depth is the number of bits stored for each pixel. More bits allow more possible colours and make the uncompressed file larger. When a low-resolution picture is enlarged, each stored pixel must cover more space. The computer may guess values between pixels, so the picture can look blurry or blocky. **Recap.** Resolution describes pixel dimensions, colour depth describes bits per pixel, and width times height times depth gives uncompressed size. *Original lesson wording, examples, assessment items, and worked steps authored for the P12 computing curriculum.* ## Practice 8 questions on this page, each with its working shown. ## Needs first - [Character Sets: Storing Text as Numbers](https://lightmysky.com/learn/computing/character-sets-storing-text-as-numbers-mt_839VNNZlp2) ## Opens up - [Digital Images as an Art Medium](https://lightmysky.com/learn/arts-and-music/digital-images-as-an-art-medium-mt_UwgfEOMPk5) - [Sampling Sound into Numbers](https://lightmysky.com/learn/computing/sampling-sound-into-numbers-mt_yTA4W-yFjy)