--- 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: 2026-09-12 --- > **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 tiny squares called pixels, and each pixel stores its colour as binary numbers, just as letters are stored as numbers with an agreed table. A simple 16 by 16 heart in two colours can map red to 1 and white to 0, which is called a bitmap. That long list of numbers is why a photo can fill storage or turn blocky when it grows too large. **Example.** Size comes from three numbers multiplied: width times height times colour depth. A 100 by 100 image with 8-bit colour takes 100 times 100 times 8, which is 80,000 bits. Double the depth to 16 and the file doubles too, since every pixel carries twice the bits. Resolution is how many pixels build the picture, and more pixels in the same space look sharper. Colour depth is how many bits store each pixel, and more depth means more possible colours. Stretch a low-resolution picture too far and it turns blurry or blocky, because the computer must guess colours it never stored. **Tip.** Work out the bit size before you save or send. Multiply the sides by the depth and you will never be surprised by a giant file. **Recap.** Resolution sets the pixel count, depth sets the bits per pixel, and their product sets the size. ## 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)