File Sizes & Storage Requirements

 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

 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

 Each pixel in the picture represents a colour.  When referring to colours we will either say: X colours X-bit colour

 X 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?

 X 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? 2 4 = 16  4 bits How many bits are needed to represent 256 colours? 2 8 = 256  8 bits

 X-bit Colours 16 bit colour 24 bit colour (We are told the number of bits required to produce the colour)

 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

 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 1024 bytes in a kilobyte 153, 600 bytes / 1024 = 150 kB To convert megabytes, we would divide by 1024 again.

 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?

 In MB what is the file size of: An image 640 x 480 in 24 bit colour? 640 x 480 x 24 = 7, 372, 800 bits 7, 372, 800 bits /8 = 921, 600 bytes 921, 600 bytes /1024 = 900 KB 900KB /1024 = 0.88MB An image 1280 x 720 using 1024 colours? 1280 x 720 x 10 = 9, 216, 000 bits 9, 216, 000 bits /8 = 1, 152, 000 bytes 1, 152, 000 bytes /1024 = 1125 KB 1125 KB /1024 = 1.1MB

 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 =

640, 000 bits 640, 000 bits /8 = 80, 000 bytes 80, 000 bytes /1024 = 78.1 KB

 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?

 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 /1024 = 5, KB 5, KB /1024 = 5 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 /1024 = 25, KB 25, KB /1024 = 24.7 MB

 Practice calculating file sizes by working through Binary Worksheet 2 in One Note. Notes: Yes you can use a calculator BUT you MUST show each step of the calculations to get full marks!!