Memory & StorageTopic Summary
Knowledge Organiser: Images and Sound
Part of Images & Sound · GCSE GCSE Computer Science revision
This topic summary covers Knowledge Organiser: Images and Sound within Images & Sound for GCSE Computer Science. Revise Images & Sound in Memory & Storage for GCSE Computer Science with 18 exam-style questions and 16 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 12 of 12 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 12 of 12
Practice
18 questions
Recall
16 flashcards
Knowledge Organiser: Images and Sound
Key Terms
- Pixel: Smallest unit of a digital image (picture element)
- Resolution: Number of pixels in an image (width × height)
- Colour depth: Number of bits used to represent each pixel's colour
- Sample rate: Number of audio samples taken per second (measured in Hz)
- Bit depth (audio): Number of bits used to store each audio sample
- Metadata: Additional data stored with an image (e.g. width, height, colour depth)
Must-Know Facts
- Image file size (bits) = Width × Height × Colour depth
- Divide by 8 to convert bits to bytes
- 24-bit colour depth = True Colour (16.7 million colours)
- Sound file size (bits) = Sample rate × Bit depth × Duration × Channels
- CD quality audio: 44,100 Hz sample rate, 16-bit depth, stereo (2 channels)
- Stereo = 2 channels; mono = 1 channel
- Higher resolution/sample rate = better quality but larger file size
Key Concepts
- Image calculation example: 100×100 pixels, 24-bit = 100×100×24 ÷ 8 = 30,000 bytes
- Sound calculation example: 44,100 Hz × 16-bit × 10 sec × 2 channels ÷ 8 = 1,764,000 bytes
- Quality vs file size trade-off: Increasing any factor improves quality but increases file size
- Always divide by 8 to convert from bits to bytes in any file size calculation
Common Mistakes
- Forgetting to divide by 8 to get bytes: The formula gives the answer in bits — divide by 8 to convert to bytes, then by 1,024 for KB etc.; omitting this step loses marks
- Confusing resolution with colour depth: Resolution is the number of pixels (width × height); colour depth is the number of bits per pixel — both affect file size independently
- Saying higher sample rate = more channels: Sample rate (Hz) measures how many times per second sound is sampled; the number of channels (mono/stereo) is a separate factor in the sound file size formula
- Mixing up image and sound file size formulas: Images use width × height × colour depth; sound uses sample rate × bit depth × duration × channels — they are different formulas