Images & Sound Representation — GCSE Computer Science Revision
Revise Images & Sound Representation for GCSE Computer Science. Step-by-step explanation, worked examples, common mistakes and exam-style practice aligned to AQA, Edexcel, OCR, WJEC, Eduqas, CCEA, Cambridge International (CIE), SQA, IB, AP.
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Go to Compression & EncryptionWhat is Images & Sound Representation?
Digital images and sound are stored by converting physical properties into binary data. For images, this is done by sampling the colour of the image at regular points, called pixels, and storing the colour as a binary number (bit depth). For sound, the amplitude of the sound wave is sampled at regular time intervals (sample rate), and this amplitude is stored as a binary number (bit depth).
Board notes: Covered by all major boards (AQA, Edexcel, OCR). You need to be able to calculate image and sound file sizes and explain how resolution, colour depth, and sample rate affect quality and file size.
Step-by-step explanationWorked example
A 1-bit black and white image of 4x4 pixels could be represented by 16 bits. A '1' could be a white pixel and a '0' a black pixel. The binary data 1111001100111111 would represent a grid with a white border and a 2x2 black square in the middle. The file size would be 16 bits (plus metadata). If we used 8 bits per pixel (colour depth), the file size would be 4 * 4 * 8 = 128 bits.
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Common mistakes
- 1Confusing image resolution with colour depth. Resolution is the number of pixels (width x height), while colour depth is the number of bits used to store the colour of each pixel.
- 2Not understanding the trade-off between quality and file size. Higher resolution, colour depth, and sample rates all lead to better quality but create much larger files.
- 3Forgetting what metadata is. This is extra data stored in the file, such as the image dimensions, date taken, or artist name, which is not part of the image or sound data itself.
Images & Sound Representation exam questions
Exam-style questions for Images & Sound Representation with mark-scheme style solutions and timing practice. Aligned to AQA, Edexcel, OCR, WJEC, Eduqas, CCEA, Cambridge International (CIE), SQA, IB, AP specifications.
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Step-by-step method
Step-by-step explanation
4 steps · Worked method for Images & Sound Representation
Core concept
Digital images and sound are stored by converting physical properties into binary data. For images, this is done by sampling the colour of the image at regular points, called pixels, and storing the c…
Frequently asked questions
How does colour depth affect an image?
Colour depth determines the number of colours available for each pixel. A 1-bit colour depth allows only 2 colours (e.g., black and white). An 8-bit colour depth allows 2^8 = 256 colours. A 24-bit colour depth (True Colour) allows over 16 million colours.
How is sound quality affected by sample rate and bit depth?
A higher sample rate means the sound wave is measured more frequently, capturing higher frequency sounds more accurately. A higher bit depth means the amplitude of each sample is stored more precisely, resulting in a greater dynamic range and less distortion.