O LevelComputer ScienceCambridge (CIE)Revision Notes1. Data RepresentationData Storage & CompressionCalculating File Sizes

Calculating File Sizes (Cambridge (CIE) O Level Computer Science)

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Robert Hampton

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Calculating File Sizes

How do you calculate the size of a bitmap image?

Calculating the size of a bitmap image can be carried out with either of the following formulas:
- Resolution x colour depth
- Image width x image height x colour depth

Example

Image Files

(Resolution) x (Colour Depth)

Size of bitmap image =
Resolution	250,000	Resolution = width x height
Colour Depth	24 bits (3 bytes)	24 bits = 3 bytes
250,000 x 24	= (bit to bytes) /8 (bytes to KiB) /1024	6,000,000 bits 750,000 bytes 732 KiB
250000 x 3	= (bytes to KiB) /1024	750,000 bytes 732 KiB

OR

Image Files

(Image width) x (Image height) x (Colour Depth)

Size of bitmap image =
Image width	500
Image height	500
Colour Depth	24 bits	24 bits = 3 bytes
(500 x 500 x 24)	= (bit to bytes) /8 (bytes to KiB) /1024	6,000,000 bits 750,000 bytes 732 KiB
(500 x 500 x 3)	= (bytes to KiB) /1024	750,000 bytes 732 KiB

How do you calculate the size of a sound file?

Calculating the size of a sound file is carried out with the following formula:
- Sample rate x duration x sample resolution

Example

Sound Files

(Sample Rate) x (Duration in seconds) x (Sample Resolution)

Size of sound file =
Sample rate	100	Samples per second
Duration	60	Seconds
Sample resolution	24	Number of bits stored per sample
100 x 60 x 24	= (bit to bytes) /8 (bytes to KiB) /1024	144,000 bits 18,000 bytes 18 KiB

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Robert Hampton

Author: Robert Hampton

Rob has over 16 years' experience teaching Computer Science and ICT at KS3 & GCSE levels. Rob has demonstrated strong leadership as Head of Department since 2012 and previously supported teacher development as a Specialist Leader of Education, empowering departments to excel in Computer Science. Beyond his tech expertise, Robert embraces the virtual world as an avid gamer, conquering digital battlefields when he's not coding.