*** This is the version with the Jim's answers.  *** 

 Term review : bandwidth and file size questions 

 A. Images

   You take a high quality photo with a digital still camera.
   You'd like the 4 inch x 6 inch image to print on 
   a 300dpi (dots per inch) color laser printer, with as 
   much color resolution as you can (24 bits per pixel).
 
     1) How big a file is the raw data for this image?

        > Well, 1MB = 1 Mega Byte = 8 * 1024 * 1024 bits
        > Then multiplying out the inches, pix/inch, and bits/pix gives
        > 
        > 4 inch * 6 inch * 300 pix/inch * 300 pix/inch
        > * 24 bits / square pixel / ( 8*1024*1024)
        > = 6 MB

     2) How big would you expect it to be when saved as 
        a medium quality jpeg?

        > We saw in class that jpeg compression can give
        > a variety of compression ratios; 20 times is typical.
	> so the final file might be 300kB or so.

 B. Audio

   You record 10 minutes of CD quality music.
   Your original data is pretty high quality, 
   without any compression.

     3) What file format might you use?

       > As describe on the wikipedia among other places,
       > .wav is a typical format.
     
     4) How big is the raw data file?

       > We need to sample at a rate of something like 44kHz
       > (44,000 samples/sec) with about 16 bits (or more) per sample.

       > So the size is something like
       > 10 min * 60 sec/min * 44,000 samples/sec
       > * 2 channels * 16 bits / (8*1024*1024 bits/MB) = 100 MB


   Now you decide to move that high quality data over the network 
   to a friend's computer.

     5) How long does it take to do that over a 56kbps phone line?

        > 100 MB = 800 Mb = 800*1024 kb where kb = "kilo-bit"
        > 56 kbps means 56 kb per second so the time is
        > 800*1024 kb / ( 56 kb / sec) = 800*1024/56 sec = 15000 sec
        > = 4 hours

     6) How long would it take over a 10Mbps intranet?

        > 800 Mb / (10 Mb / sec) = 80 seconds = a minute and a half

   Next you compress it to an mp3 file.

     7) How big is the mp3 file?

        > mp3 gives about 10 times compression, so the file is about 10MB = 80Mb
 
   And finally you decide to stream it to your friends.

     8) How much bandwidth do you need (in bps) to stream the audio?
        (Divide the size of the file in bits by the time to play it.)

        > We want to send a 10MB file in 10 min = 600 sec
        > The required bandwidth is something like 
        > (8 bits/Byte * 10MegByte *1024 k/M) / (10*60 sec)
        > = (8*10*1024/600) kbps = 130 kbps
        > which is well within intra-net speeds, but beyond dial-up (56kbps) speeds.

 C. Video

   So let's do some of those calculations with video, eh?

   You record with your camcorder 10 minutes of 
   DV quality video, with one of our school digital cameras.
   The raw data is in a form that FinalCut can edit.

     9) How big is the DV (what comes off the miniDV tape) file?
        Will that fit on a CD?  On a DVD?

        > From our class notes, the miniDV format is 25Mbps.
        > Note that this is about a quarter of the raw data rate of 
        > (720x480 pixels ) x 30 frames/sec x ( 8 greyscale bits + 4 color bits) 
        > = 120 Mbits/sec

        > That means that 10 minutes is 
        > 10*60*25Mbps / 8 bits/Byte / 1024 Gig/Meg = 1.8 GB (GigaBytes)
        > A typical CD holds about 700 MB (or 0.7 GB) 
        > while a DVD holds 10GB or so.

        > So it won't fit on a CD.  It will fit on a DVD.

    10) How long would it take to move that to another
        computer on the campus intranet, at 10Mbps?

        > 1.8GB * 1024 MB/GB * 8b/B / (10 Mb / sec) = 1500 sec = 25 min

   Now you compress that 10 minutes to DivX format (e.g. mpeg4).

    11) How big is it as a DivX file?  Will that fit on a CD?

        > From our class notes (or the wikipedia),
        > DivX is an MPEG-4 compression scheme which uses 3 to 15 Mbps,
        > which means its about 5 times faster or smaller than the miniDV format.

        > So the file is about 1.8GB/5 = 350 MB which is about half of a CD

   And again you decide to stream it.

    12) How much bandwidth do you need (in bps) to stream the video?
        (Again, divide the size of the file in bits by its run time.)

        > We already have the bandwidth directly from the class notes, 
        > 5 Mbps or so, or about half of a 10Mbps intranet line.