Binary 4 File Sizes

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

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

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)

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?

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

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

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 = 153.6 kB To convert megabytes, we would divide by 1000 again.

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?

Calculating File Size: Images 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 /1000 = 921.6 kB 921.6kB /1000 = 0.92MB 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 /1000 = 1152 kB 1152 kB /1000 = 1.15MB

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 =

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

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?

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 44000 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 96000 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