From: agough@sedona.intel.com (Andy Gough~)
Newsgroups: rec.video,rec.photo,rec.arts.books
Subject: Re: Photo CD
Date: 23 Jan 1993 00:14:45 GMT
Organization: "Intel Corporation"
Distribution: world
Reply-To: agough@sedona.intel.com
NNTP-Posting-Host: tasmania.intel.com
Originator: agough@sedona


In article <C0Czyn.H23@athena.cs.uga.edu>, fuller@athena.cs.uga.edu (James P. H. Fuller) writes:
> CUNY/Spartacus <I18BC@CUNYVM.BITNET> writes:
> 
> >>Digital (mostly magnetic) media seems to go out of fashion very fast.
> >>Have you tried to read a 7-channel tape lately? A punched tape?
> >>Can we be certain that somebody a hundred years from now can read a
> >>PhotoCD?
> >
> >Sorry Per,
> >      But you ought to know better than that being a computer person.
> >If its digital, it can be transfered to many different digital mediums.
> >Just like transfering an old text file from a 160k 5 1/4 floppy
> >to a 2.88mb  3 1/2 floppy.   Or uploading my floppy file to 3380
> >mainframe diskpack or digital tape.  etc etc etc...etc
> >
> >The resolution argument I understand, but this?
> 
> 
>     Sure, it *could* be transferred, but what if nobody bothers to transfer
> it until all the devices that can read it are junked?  I happen to have a
> recording of my grandfather's voice that I can't play.  It's a *wire*
> recording.  Right, like a tape recorder only the stuff on the reels is a
> strand of wire.  Dates from early 1940s, I think.  You got anything that
> will read this?  Or consider the contortions I had to go through when I
> recently wanted to get a file from a 140K Apple II disk, circa 1980, onto
> my 486.  Locate ancient Apple, blow off cobwebs, clean and lubricate disk II
> drive (whoopee, it still works!), locate vendor of serial port cards for
> ancient Apple (whoopee, one or two still exist), rig up null modem, ftp
> Apple II kermit and Unix C-kermit from Columbia to my work host, transfer 
> both to 486 via zmodem, compile C-kermit for SysV, get Apple kermit *to* 
> the Apple *without* a comm program to receive it (a nice trick), get it
> working, dream up a gettydefs entry for 486 serial port to the Apple, start
> Apple kermit, log into Unix from Apple, invoke C-kermit server, shoot file
> over.  It took almost a week of evenings just to teleport this old file
> forward a mere 13 years.  
> 
>     I'd like very much to play with some of the IMMENSE amount of data that
> has been generated by satellites and other space probes over the years but
> I can't because almost all of it is archived offline on reels of tape that
> nobody is EVER going to bother to transcribe onto more recent media.  It
> might as well never have been collected.
> 
>     I've bellowed the following in this forum before:  COMPUTERS ARE NOT A
> SUBSTITUTE FOR BOOKS.  If you want to be sure some archive is readable a
> hundred (let alone a thousand) years hence, you better make sure it's written
> on something that's human-readable *without* any doodads or technical infra-
> structure.
> 
>                                                   -- jf

This view surprised me when I read it, as I had recently been thinking
a lot that Photo CD would be ideal for long-term (generational) archival
storage of photographs.

The advantages I see are:
	1) No degredation of the image over time (due to digital encoding)
	2) Compact storage (takes up less space than prints+negatives)
	3) Ability to create computer database that references photos on PhotoCD
	4) Ability to download images to my computer's hard disk, edit them
	   (cropping, color correction, special effects), and eventually be able
	    to transfer them back to PhotoCD (hopefully).
	5) Digital data makes it easy to update to next storage technology.
	6) Possible use of error correcting codes and redundancy.
	7) Backups of the same quality can be made.

So, I feel that PhotoCD will allow me to gather up all my old family photographs
and create PhotoCD albums for my descendents--so they can know what their great 
great great grandfather looked like.  Granted, when they view it, it may not be on
a "PhotoCD" anymore--it may be stored in a protein crystal--but it will be the same
quality that I see today.

The disadvantages I see are:
	1) Current cost of transferring single slides onto PhotoCD
	2) The need to transfer the data to new storage mediums in the 
	   future.
	3) Currently no way to add edited images back onto the PhotoCD

Storage Obsolescence:
~~~~~~~~~~~~~~~~~~~~
     While one doens't usually think of it at the time, the choice of a storage
medium also carries an implicit choice on how long you want to store something.
Some storage media last longer than others.  "Post-It" notes are for very short-term
storage.  An etched gold plate is for extremely long-term storage.
      So, I think that if one wants to preserve old information, the transfer should
take place when you adopt the new technology.  Note also that most data and books
aren't worth saving for 100 years.

Film Storage:
~~~~~~~~~~~~
     Film degrades over time due to chemical reactions and ultraviolet radiation.  
Specifically, the color dyes in color film fade over time.  To slow this, one can
store the negatives in a humidity-controlled refrigerator.
     To store film images for a long time, one needs to use black and white film,
which doesn't degrade as fast as color film.  Note that one can store separate 
b&w images for the red, green, and blue portions of a color image--this will last
longer.

Paper Storage:
~~~~~~~~~~~~~
     Paper can obviously last a long time.  One should use acid-free paper and
good ink.  This helps prevent the paper falling apart and the ink fading.
      I don't know how long photocopier toner particles will stick to the paper.
      Paper has some disadvantages, of course.  It tends to be degraded the more
it is handled (rips, smudges, creases, etc.).  It's also bulky and heavy.

CD Storage:
~~~~~~~~~~
     There has been a lot of controversy on the lifetime of Compact Discs.  Properly
manufactured, they should last a long time (decades), but they won't last forever.
     The principle mechanism of degradation appears to be chemical change of the 
aluminum reflecting layer.  Oxygen, water, and other reactants (I assume), diffuse 
through the lacquer coating (or through a pinhole) and react with the aluminum, to 
form Al2O3 (otherwise know as safire) that is translucent and not as reflective.
Thermal cycle stress (due to different coefficients of thermal expansion between the
aluminum, lacquer, and polycarbonate) introduces cracks that can 1) facillitate
contaminant diffusion, 2) act on the bit data itself.
      One can greatly extend the life of a CD by:
	1) using gold (Au) as the reflective layer, as gold is less reactive
	2) a thick, pinhole-free, lacquer coating
	3) inks with low diffusion constants through the lacquer.
	4) storing the CD at low temperature and low humidity, with a slow ramp-up
	   to room temperature before use.

I saw some data from Mobil Fidelity (makers of the UltraDisc series) that compared
an UltraDisc (a well manufactured disc, with a gold reflecting layer) to a regular
CD through two types of stress test:  steam and temperature cycling.  As I remember
it, the regular CD lasted only two or three cycles before substantial error rates were
present.  The UltraDisc sailed right through, with little degradation--orders of magnitude
less.  I suppose one can still get the data from Mobil Fidelity.
     Now, if one is concerned about future generations being able to read the "lost
knowledge of our era" from a degraded compact disk (i.e., in 20,000 years), I would
assume that, if the disc is intact, that an electron microscope could be used to read
the presence/absence of pits in the aluminum layer.  This could be kindof slow.

The Arrhenius Equation:
~~~~~~~~~~~~~~~~~~~~~~
     t1 = t2 * exp[(Ea/K)*(1/T1 - 1/T2)]
       where:
	t1 = mean time to failure at T1
	t2 = mean time to failure at T2
	K  = Boltzmann's constant (8.62E-5 eV/K)
	T1 = temperature 1 (in Kelvins)
	T2 = temperature 2 (in Kelvins)
	Ea = thermal activation energy (eV)

     To me, the bottom line for preserving film and compact discs is to store them at
low temperature--say in a refrigerator at 50 'F.  The equation above shows that the 
rate of a chemical reaction will decrease exponentially as temperature is decreased.  So,
one can apply this knowledge and extend the life of a compact disc (say, normally 40 years
at room temperature) and by storing it at low temperature multiply its lifetime by two
or three orders of magnitude.
      Of course, with low temperature storage, one must be careful that:
	1) Humidity is controlled in the refrigerator
	2) No water condensation occurs on the disc during cool down or warm-up
	3) That the disc is gradually cooled and warmed up (to reduce thermal stress)

This is more work than most people will be willing to put up with, though.

Regards,
Andy
-- 
 Andy Gough			|  Internet: agough@sedona.intel.com
 Intel Corporation  CH3-36	|            agough@az.intel.com
 5000 W. Chandler Blvd.		|      "Knowledge is power."
 Chandler, AZ  85226		|                -- Francis Bacon
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