Data Representation · 4 question types
Past paper frequency (2018 to 2024)
This topic accounts for approximately 4% of your exam marks.
File size calculations and lossless vs lossy compression are regular 3 to 4 mark questions.
These formulas were introduced in topic 2; they appear constantly in topic-3 questions too.
file size (bits) = sample rate (Hz) × sample resolution (bits) × duration (seconds)
Example — A sound clip lasts 60 seconds, with a sample rate of 100 Hz and a sample resolution of 24 bits. Calculate the file size in kB (1 kB = 1000 bytes).
file size (bits) = image width (pixels) × image height (pixels) × colour depth (bits per pixel)
Example — A bitmap measures 500 × 500 pixels with a colour depth of 24 bits. Calculate the file size in kB (1 kB = 1000 bytes).
Shortcut: since 24 bits = 3 bytes, you can multiply width × height × 3 (bytes per pixel) directly to get bytes without going through bits. The answer is the same.