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AQA · GCSE · Computer Science · Higher

Bitmap storage size calculation

Q05.3 2 marks

Figure 2 shows four bitmap images.

Figure 2
Figure 2

Figure 2

Enlarged question image

Figure 2

Calculate the minimum amount of storage required to store Image D from Figure 2.

Give your answer in bytes.

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Marking points

  1. 1 For full credit, reaches 10 bytes.
  2. 2 If the final answer is wrong, check for one official working-mark step.

Full-mark answer

Image D contains 40 pixels and needs 2 bits per pixel, so it needs 40 × 2 = 80 bits. 80 ÷ 8 = 10 bytes.

Why this answer loses marks

I multiplied the pixels by the colour depth and stopped at bits.

That finds bit storage, but the question asks for bytes, so the unit conversion is still needed.

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