Calculate file sizes of image

1.2.4c Data Storage: Images

Data Storage: Images — Note 1 of 4

What you need to know

Image file size is calculated using the formula: colour depth x image height (pixels) x image width (pixels). The result is usually in bits and may need converting to bytes or larger units.

What to know

Image file size = colour depth × image height × image width (pixels).
Example: 100×200 pixels, colour depth of 24 bits = 100 × 200 × 24 = 480,000 bits = 60,000 bytes = 60 KB.
This formula gives the RAW/uncompressed file size — actual file sizes may be smaller due to compression.

Exam technique

Tip:Always show your working and check which UNITS the answer requires (bits, bytes, KB, MB).
Mistake:Forgetting to convert between bits and bytes. Divide by 8 to go from bits to bytes.

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