U of S | Mailing List Archive | alt-photo-process-l | Re: Digital Film backup

Re: Digital Film backup

----- Original Message ----- From: "Dan Haygood" <dan@haygoods.org>
To: <alt-photo-process-l@usask.ca>
Sent: Tuesday, June 12, 2007 8:44 PM
Subject: Re: Digital Film backup

An image on a (home made) CD is a dye-based spiral photograph of a digital
encoding of the image. The photograph is not latent; the dye changes
state upon direct application of high-intensity light, so it doesn't need
to be developed. It also seems to stay that way, so it doesn't need to be

Because it's dye-based, it's probably a good idea to copy the image to new
media (i.e. make a new CD) every once in a while. Fortunately, the copy
will be exact, not suffering from generational degradation.

If we (as a species) can still decipher cuneiform now, we'll still be able
to decipher--with the help of a microscope--ISO9660 spiral pictures of
JPEGs for thousands of years into the future, barring intermittent erasure
of all human knowledge in nuclear (or what have you) armageddons. By
then, the majority of historical images, however filtered by various
"social importance" filters through the eons, will have been transferred
to new encodings and new media.

But, one could always store images in a less-intensive simple encoding
(say, a bit map), and hammer the data into titanium. That, along with a
Voyager-style line image of a prism and spectrum with marks for R, G, and
B, should allow the most primitive of species to recover a digitized
image. I doubt the colorguide picture would even be needed, given how
clever we are right now.

So the only issues seems to be the appreciation of the image without
decoding, and whether or not analog chemical images can ever be adequately
digitized, and what to do until then, if they can.

- Dan
A couple of things: Dyes, in general, are fugitive. In particular application of strong UV light can fade many types of dyes.
However, the "image" on a CD or DVD need not be made of dye, in fact, most commercial optical discs have tiny pits which interfere with the transmission of light. The life of these discs seems to be limited mainly by the life of the reflective layer on one side. It seems to me that a lot of improvement could be made by finding better ways of protecting the deposit than are generally employed now. Also, other methods of recording a digital bit stream could be used such as your suggestion of making a CD or a noble metal. Other possibilities suggest themselves.
It is possible to have a very high degree of error immunity by using a holomorphic method of recording the data. Current methods provide a large amount of redundancy to accomplish this but, I suspect, it would be possible to make a recording which could withstand a great deal more physical damage than a CD and still be recoverable.
The problem of maintaining the recovery technology remains but the argument against digital storage because of the need for migrating the information to a new format periodically is partly specious since other forms of data storage also need periodic copying as the strorage media become degraded. Nonetheless, the fact that microfilm can be read with no more aid than a strong magnifying glass suggests such relatively simple technology should continue to have a place in a world increasingly dominated by very complex technology.

Richard Knoppow
Los Angeles, CA, USA