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Data units, images and sound
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How big is a photo or a song file? You can calculate it from how the data is stored.
Units of size
8 bits = 1 byte.
In binary units, 1 kibibyte (KiB) = 1024 bytes, 1 mebibyte (MiB) = 1024 KiB, and so on.
In decimal units, 1 kilobyte (kB) = 1000 bytes. Use whichever the question asks for.
In binary units, 1 kibibyte (KiB) = 1024 bytes, 1 mebibyte (MiB) = 1024 KiB, and so on.
In decimal units, 1 kilobyte (kB) = 1000 bytes. Use whichever the question asks for.
Images
A bitmap image is a grid of pixels. Colour depth is the number of bits per pixel.
File size (bits) = width × height × colour depth
More pixels (higher resolution) or more colours means a bigger file.
File size (bits) = width × height × colour depth
More pixels (higher resolution) or more colours means a bigger file.
Sound
Sound is sampled. Sample rate is samples per second (Hz). Bit depth is bits per sample.
File size (bits) = sample rate × bit depth × seconds (for one channel)
Divide bits by 8 to get bytes.
File size (bits) = sample rate × bit depth × seconds (for one channel)
Divide bits by 8 to get bytes.
An image is 100 × 100 pixels with a colour depth of 8 bits. Find its size in bytes.
- bits = 100 × 100 × 8 = 80 000 bits
- bytes = 80 000 ÷ 8
- = 10 000 bytes
Answer: 10 000 bytes
8 bits = 1 byte; 1 KiB = 1024 bytes. Image bits = width × height × colour depth. Sound bits = sample rate × bit depth × seconds. Divide by 8 for bytes.
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