Detailing the various calculations that are used to estimate storage requirements of various multimedia types

1. The Memory of GraphicsThe Memory of Graphics
(Calculations involved in(Calculations involved in
displaying multimedia)displaying multimedia)

2. • Images place extra demands upon
multimedia systems.
• The current image being displayed is
stored in a section of memory called the
frame buffer.
• Large, high resolution images may affect
the performance of a multimedia
presentation.
• The relationship between the image on the
screen and the bits in memory is called bit
mapping or memory mapping.

3. • The storage requirements of an image are
dependent upon:
• the number of pixels
• the number of colours / tones
• Bit depth is the number of bits required per
pixel.
• Each extra bit per pixel doubles the
number of possible tones or colours.
• [COPY Table 7.1, p.223]

4. • To calculate the size of an image we must
multiply the number of pixels by the bit
depth.
• E.g. What is the size in kilobytes of a 256
colour image displayed on a screen with a
resolution of 1024 x 768 pixels.
• File size = dimensions x bit depth
= 1024 x 768 x 8 / 8 x 1024
= 768 Kb.

5. • Video of any kind is just a series of still
images that are played one after the other.
• This means that to calculate the memory
requirements of any video/animation we
expand upon the formula we already have.
• We use the file size for one image
multiplied by the number of frames per
second (frame rate) multiplied by how
many seconds of video there is.

6. • E.g. What is the file size, in gigabytes, for a
90 minute video in 32 bit colour with a
resolution of 2048 x 872 being broadcast at
24 fps?
• Number of frames = frame rate x seconds
= 24 x 90 x 60
= 129 600 frames
• Frame file size = resolution x bit depth
= 2048 x 872 x 32
• Total size = 24 x 90 x 60 x 2048 x 872 x 32 /
8 x 1024 x 1024 x 1024

7. • Audio files are different because of how they
are displayed.
• All sound must be converted from an analog
to digital form.
• This digitisation of sound is called sampling.
• The quality of the sound is determined by its
sampling rate and sample size, as well as
whether the sound is mono or stereo.
• The sampling rate is the number of times a
slice (sample) is taken of a sound wave per
second.

8. • Two common sampling rates are 44.1 kHz
(44100 samples per second) and 22.05 kHz
(22050 samples per second).
• The more samples, the better the sound.
• The sample size is the number of bits per
sample.
• The more bits per sample, the higher the
quality.
• Two common bit-rates are 8 bit and 16 bit
sound.

9. • Stereo requires two audio streams while
mono only needs one.
• E.g. Calculate the file size (in Mb) of a three
minute stereo audio track that has been
recorded using 16 bit sound and a sampling
rate of 44.1kHz.
• = sample rate x sample size x time x 2
• = 44100 x 16 x 3 x 60 x 2 /
8 x 1024 x 1024

10. • Stereo requires two audio streams while
mono only needs one.
• E.g. Calculate the file size (in Mb) of a three
minute stereo audio track that has been
recorded using 16 bit sound and a sampling
rate of 44.1kHz.
• = sample rate x sample size x time x 2
• = 44100 x 16 x 3 x 60 x 2 /
8 x 1024 x 1024