Representing Text, Images and Sound
Encoding characters, bitmap images and sampled sound as binary data and explaining quality-storage trade-offs.
How to study for GCSE Computer Science
Move repeatedly between problem, algorithm, trace, code, test evidence and system explanation; use the exact language and assessment format required by your current board.
Core concepts
Concept 1
Character encoding maps characters to numeric codes; the character set determines which symbols can be represented.
Exam cue: Separate the abstract character from its numeric code and binary encoding.
Concept 2
A bitmap records pixel values, with resolution and colour depth influencing detail, colour range and raw size.
Exam cue: Calculate raw image size from dimensions and colour depth using consistent units.
Concept 3
Digital sound samples an analogue signal, with sample rate, sample resolution and duration determining fidelity and raw data size.
Exam cue: Calculate raw sound size from sample rate, sample resolution, channels and duration when supplied.
Risk pitfalls and guardrails
Assuming one character always occupies one byte in every encoding.
Guardrail: Do not substitute one board's syntax, protocol list, language version or extension topic for the multi-board core; check the current specification and exam year.
Confusing image resolution with colour depth.
Guardrail: Do not substitute one board's syntax, protocol list, language version or extension topic for the multi-board core; check the current specification and exam year.
Treating sample rate and sample resolution as the same property.
Guardrail: Do not substitute one board's syntax, protocol list, language version or extension topic for the multi-board core; check the current specification and exam year.
Memory anchors
Character set
The collection of characters an encoding can represent.
Character encoding
A mapping between characters and numeric codes.
Pixel
The smallest addressable picture element in a bitmap.
Colour depth
The number of bits used to represent a pixel's colour.
Sample rate
The number of sound measurements recorded per unit time.
Checkpoint rule
Do the check-up only after you can summarize each concept in one sentence and identify one dangerous pitfall from memory.
Knowledge Check (after reading)
Short check-up to confirm understanding of this module.
Check-up Questions
What does a character set provide?
Why can the same bit pattern display as different characters under different encodings?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
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