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Images, sound and the limits of bits
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The number of bits you use decides how much detail you can store. More bits means better quality but bigger files.
States from bits
n bits can represent 2n different values (states).
1 bit: 2 states. 4 bits: 16. 8 bits: 256.
To store at least 50 different values you need 6 bits, because 25 = 32 is too few and 26 = 64 is enough.
1 bit: 2 states. 4 bits: 16. 8 bits: 256.
To store at least 50 different values you need 6 bits, because 25 = 32 is too few and 26 = 64 is enough.
Bitmap images
A bitmap is a grid of pixels. Resolution is the number of pixels (width × height).
Colour depth is the number of bits per pixel: 1 bit gives 2 colours, 8 bits give 256, 24 bits give over 16 million.
Higher resolution or colour depth: better image, bigger file.
Colour depth is the number of bits per pixel: 1 bit gives 2 colours, 8 bits give 256, 24 bits give over 16 million.
Higher resolution or colour depth: better image, bigger file.
Sound
Sound is an analogue wave. The computer measures its amplitude (height) at regular intervals: sampling.
Sample rate: samples per second (Hz). Sample interval: time between samples = 1 ÷ sample rate.
Bit depth: bits per sample. More bits give more possible amplitude levels, so the recording is closer to the original.
Limitation: too few bits or samples gives a poorer copy of the original sound.
Sample rate: samples per second (Hz). Sample interval: time between samples = 1 ÷ sample rate.
Bit depth: bits per sample. More bits give more possible amplitude levels, so the recording is closer to the original.
Limitation: too few bits or samples gives a poorer copy of the original sound.
A sound is sampled at 50 000 Hz. What is the sample interval in microseconds?
- Sample interval = 1 ÷ 50 000 s = 0.00002 s
- 0.00002 s × 1 000 000 = 20 microseconds
Answer: 20 microseconds
n bits give 2n states. Image quality depends on resolution and colour depth. Sound quality depends on sample rate and bit depth. Sample interval = 1 ÷ sample rate.
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