Huy
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There's a thread in this forum on it.
Calculating time for data transmission!
http://www.boredofstudies.org/community/showthread.php?s=&threadid=13682
The Catholic (CSSA) trial did and asked for the time of transmission, given the transmission rate (speed) and filesize.
You could also be asked to calculate file sizes (such as memory and frame buffers) and the usual file storage sizes for audio and video files (mostly contained in the Multimedia Systems option).
So you should know how to answer things like:
a. Calculating the number of bits
You know that the resolution = horizontal pixels x vertical pixels
Now taking the resolution, multiply that by the bit depth.
Now you've got your file size in bits.
b. Calculating the number of bytes.
Same deal, but take the total number of bits and divide by 8 (8 bits per byte).
c. Calculating the number of kilobytes
Take the number of bytes, and divide by 1024.
Now you've got your file size going from bits, to bytes (divide by 8) to kilobytes (divide by 1024)
For bit-mapped images
Usually, file size questions for bit-mapped images will ask for the number of bytes or kilobytes,
File size for an image = (resolution x bit depth) / (8 * 1024)
The answer is now in kilobytes, if the question asked for bytes, then you would leave out 1024, and have:
File size for an image = (resolution x bit depth) / 8
For audio files
File size = sample rate x bit resolution x time x channels
The sample rate (in hertz) = the number of 'slices' (or sample) taken from a sound wave per second.
The bit resolution (in bits) is the measure of how many bits per sample (this is also known as the sample size)
Time is measured in seconds, it's just how long the audio file is (in duration/length)
The number of channels can be mono (one channel) or stereo (two channels).
For video files
File size = bit resolution x frames per second x time
Where the only difference between audio and video file size calculations lies in the channels and sample rate.
The sample rate can then be compared to the number of frames per second (or 'slices') in an audio file.
This is how I like to remember the three:
Images:
pixels across image times pixels down the image, times the bit depth (or how many bits which can hold a particular colour or shade), all over 8 - leaving my answer in bytes.
Audio:
How many slices/samples times how many bits per slice times how long the audio goes for times the number of channels you have.
Video:
The bit resolution (much like an audio file's sample size, or the number of bits per frame) times it by how fast the video moves (frames per second) times it by how long the video lasts.
