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A-LevelComputer ScienceData representation9618/12 · Oct/Nov 2022 · Q88 Marks

The following bitmap image has a resolution of 4096 × 4096 pixels and a colour depth of 24 bits per pixel. [Figure: Black rectangle with a white arrow extending from its right side.] The image is displayed on a monitor that has a screen resolution of 1920 × 1080 pixels. A second bitmap image is stored using a colour depth of 8 bits per pixel. The file is compressed using run-length encoding (RLE).

  1. (a)Tick (✔) one box in each row to identify the effect of each action on the image file size. [Table: Action, Increases the file size, Decreases the file size, No change to the file size][2]
  2. (b)State two benefits of creating a vector graphic instead of a bitmap image.[2]
  3. (c)(i)The table shows the compressed and uncompressed values for parts of the image file. Each colour of the pixel in the image is represented by a hexadecimal value. Complete the table. The first row has been completed for you. [Table: Uncompressed image, RLE compressed image][2]
  4. (c)(ii)RLE is an example of lossless compression. Explain why lossless compression is more appropriate than lossy compression for a text file.[2]

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2022). The mark or mark type is shown in brackets.

  1. [1] Action: Change the colour depth of the image file to 16 bits per pixel. -> Decreases the file size
  2. [1] Action: Change the screen resolution to 1366 x 768 pixels. -> No change to the file size
  3. [1] Action: Change the colour of the rectangle from black to red. -> No change to the file size
  4. [1] can be enlarged without pixelation / loss of quality
  5. [1] individual components of the image can be edited
  6. [1] generally a smaller file size
  7. [1] Uncompressed sound: AB AB FF FF 1D 67
  8. [1] RLE compressed sound: 232 180 281 (for 32 32 80 81 81)
  9. [1] all the data is required // no data can be lost
  10. [1] otherwise text file will be corrupted / not make sense

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About this question

Topic
Data representation, A-Level Computer Science (syllabus 9618). Structured question, 8 marks.
Source
A-Level Computer Science, Oct/Nov 2022 Paper 1 Variant 2, question 8.

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