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Data

Bitmap images

  • 3 things to know
  • Paper 1

Overview

Pixels, resolution and colour depth, how many colours a given depth allows, the bitmap file size expression, and worked calculations in bytes and KiB.

What you need to know

Answer each one before you reveal it.

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Numbers

What is colour depth, and how many bits are needed for 16 or 256 colours?

Key term

How is a bitmap image represented in binary?

Key term

What is a pixel?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    How is a bitmap image represented in binary?

    Model answer

    A bitmap image is a grid of pixels. Each pixel's colour is stored as a binary number.

  2. 2

    What is a pixel?

    Model answer

    A pixel is the smallest single dot of colour in a bitmap image. The name is short for picture element.

  3. 3

    What is meant by the resolution of a bitmap image?

    Model answer

    Resolution is the number of pixels in an image, given as width × height. An image of 1920 × 1080 has 1,080 rows of 1,920 pixels.

  4. 4

    What is colour depth?

    Model answer

    Colour depth is the number of bits used to store the colour of each pixel.

  5. 5

    How many colours can an image with a colour depth of 4 bits show?

    Model answer

    A colour depth of 4 bits allows 16 different colours. Four bits give 2⁴ = 16 patterns.

  6. 6

    What colour depth does an image need to show 256 colours?

    Model answer

    A 256-colour image needs a colour depth of 8 bits. Eight bits give 2⁸ = 256 patterns.

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