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The Digital Camera Trick
The Digital Camera Trick
Your phone camera doesn't actually "take a picture" - it takes millions of tiny measurements! Each pixel (dot) gets 3 numbers: how much red (0-255), how much green (0-255), how much blue (0-255). A 12-megapixel photo = 12 million pixels × 3 colors × 1 byte = 36 MB! Similarly, recording sound means measuring air pressure thousands of times per second. CD quality = 44,100 measurements per second × 2 ears × 2 bytes = 176 KB/second. Digital media isn't magic - it's just lots and lots of numbers!
Deep Dive: Digitizing the Analog World
The real world is analog - continuous, infinite detail. Light bounces everywhere, sound waves are smooth curves. But computers can only store digital data - discrete numbers.
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Exam Tips - Images & Sound
Most common exam questions:
- "Calculate image file size" → Width × Height × Color Depth ÷ 8
- "Calculate sound file size" → Sample Rate × Bit Depth × Duration × Channels ÷ 8
- "What is a pixel?" → Smallest unit of a digital image (picture element)
- "What is sample rate?" → Number of samples per second (Hz)
- "Higher sample rate = ?" → Better quality but larger file
Image calculation tips:
- Always multiply: Width × Height × Color Depth
- Don't forget to divide by 8 to convert bits → bytes
- Watch out for units: KB, MB, or bytes?
- 24-bit color = True Color (most common)
Sound calculation tips:
- Four factors: Sample Rate × Bit Depth × Duration × Channels
- Stereo = ×2 channels (don't forget!)
- Duration must be in seconds
- Divide by 8 for bytes
- CD quality = 44,100 Hz, 16-bit, stereo
Common mistakes to avoid:
- Forgetting to divide by 8 (bits → bytes)
- Missing "× channels" for stereo sound
- Confusing width/height order
- Not converting duration to seconds
- Mixing up sample rate (Hz) with bit depth (bits)
Now try it yourself
Quiz · Question 1 of 18
What does colour depth refer to in a digital image?
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This topic in real past papers
Every real exam question we've found on images & sound, with a full worked answer.