1. Binary 4
File Sizes

2. Calculating File Size: Images
An image has a width in pixels and a height in pixels
Start by calculating the number of pixels all up
640 x 480=
640 wide
480 high

3. Calculating File Size: Images
An image has a width in pixels and a height in pixels
Start by calculating the number of pixels all up
640 x 480=
307,200 pixels
640 wide
480 high

4. Calculating File Size: Images
For each pixel in the picture we need to specify a particular colour from a range of possible colours.
We can give either:
The colour depth
e.g. 24-bit colour
The number of colours
e.g. 16 million colours (224=16,777,216)

5. Calculating File Size: Images
Number of colours
If the image is plain black and white (no grey) then it uses 1 bit to represent each pixel
How many bits are needed to represent 16 colours?
How many bits are needed to represent 256 colours?

6. Calculating File Size: Images
Number of colours
If the image is plain black and white (no grey) then it uses 1 bit to represent each pixel
How many bits are needed to represent 16 colours? 24= 16  4 bits
How many bits are needed to represent 256 colours? 28 = 256  8 bits

7. Calculating File Size: Images
So to calculate the file size we multiply the number of pixels by the number of bits to represent each pixel
640 x 480= 307,200 pixels
Using 16 colours = 4 bits
307,200 x 4 =
1, 228, 800 bits

8. Calculating File Size: Images
To convert 1, 228, 800 bits to kilobytes…
There are 8 bits in a byte:
1, 228, 800 bits / 8 = 153, 600 bytes
There are 1000 bytes in a kilobyte
153, 600 bytes / 1000 = kB To convert megabytes, we would divide by 1000 again.

9. Calculating File Size: Images
In MB what is the file size of:
An image 640 x 480 in 24 bit colour?
An image 1280 x 720 using 1024 colours?

10. Calculating File Size: Images
In MB what is the file size of:
An image 640 x 480 in 24 bit colour? x 480 x 24 = 7, 372, 800 bits 7, 372, 800 bits /8 = 921, 600 bytes 921, 600 bytes /1000 = kB kB /1000 = 0.92MB
An image 1280 x 720 using 1024 colours? x 720 x 10 = 9, 216, 000 bits 9, 216, 000 bits /8 = 1, 152, 000 bytes 1, 152, 000 bytes /1000 = 1152 kB kB /1000 = 1.15MB

11. Calculating File Size: Sound
To calculate the size of a sound file we multiply the:
Time length of the audio clip: 20 second
The rate at which it was sampled: 4 kHz (remember that kilo means 1000!!)
The audio quality: 8 bit audio
20 seconds x (4KHz x 1000)hertz x 8 bit =

12. Calculating File Size: Sound
20 seconds x (4KHz x 1000)hertz x 8 bit =
640, 000 bits
640, 000 bits /8 = 80, 000 bytes
80, 000 bytes /1000 = 80 kB

13. Calculating File Size: Sound
In MB what is the file size of:
A 60 second audio clip, sampled at 44KHz, using 16 bit audio?
A 1.5 minute audio clip, sampled at 96KHz, using 24 bit audio?

14. Calculating File Size: Sound
In MB what is the file size of:
A 60 second audio clip, sampled at 44KHz, using 16 bit audio? 60 x x 16 = 42,240,000 bits 42,240,000 bits /8 = 5,280,000 bytes 5,280,000 bytes /1000 = 5,280 kB 5,280 kB / 1000 = 5.28 MB
A 1.5 minute audio clip, sampled at 96KHz, using 24 bit audio? 90 x x 24 = 207,360,000 bits 207,360,000 bits /8 = 25,920,000 bytes 25,920,000 bytes / 1000 = 25,920 kB 25,920 kB / 1000 = 25.9 MB