Image file sizes

To work out the file size for an image you need to know 3 things:

its width, its height, and its colour depth

What do you do with these 3 numbers to find the number of bits needed to store the image?

• Add them

• Multiply them

• Divide them

• Subtract them

Work out the number of bits needed to store an image with these properties:

Width 30 pixels

Height 10 pixels

Colour depth 4

Work out the number of bytes needed to store an image with these properties:

Width 50 pixels

Height 10 pixels

Colour depth 4

Work out the number of bytes needed to store an image with these properties:

Width 160 pixels

Height 95 pixels

Colour depth 16

Work out the number of bytes needed to store an image with these properties:

Width 2500 pixels

Height 1800 pixels

Colour depth 12

• 275000 B

• 275 KB

• 0.275 MB

• 0.000275 GB

Answer explanation

The file size should be a number between 1 and 999, so 275 KB is the best option.

• 3800000 B

• 3800 KB

• 3.8 MB

• 0.0038 GB

Answer explanation

The file size should be a number between 1 and 999, so 3.8 MB is the best option.

Work out the most appropriate file size for an image with these properties:

Width 240 pixels

Height 250 pixels

Colour depth 4

Work out the most appropriate file size for an image with these properties:

Width 3600 pixels

Height 2700 pixels

Colour depth 16

A designer creates a square image that is 600 pixels wide.

The file size for the image is 720 KB.

What colour depth did the designer use?