X-Message-Number: 8224
Date: Tue, 20 May 1997 10:02:13 -0400 (EDT)
From: Charles Platt <>
Subject: Faded Memories

Personally I can think of other things about cryopreservation that worry 
me more than the prospect of deteriorating color photos; but if someone 
is concerned about preserving true color, clearly the picture should be 
scanned, digitized, and then stored in a NON-magnetic, NON-proprietary, 
simplest-possible format. 

A plain ordinary sheet of letter-size paper can easily store 20,000
characters (i.e. letters and spaces) if we use a small font size. We can
use them in pairs to store hexadecimal numbers from 00 through FF (decimal
values 0 through 255). Thus, the paper can store 10,000 byte values of
one additive primary color (red, green, or blue) from a typical 24-bit 
computer display in which each pixel on the screen is represented by 1 
byte for red, 1 for blue, 1 for green.

Suppose we scan a 4x6 photo into the computer at 300 dpi. That's slightly 
more than 2 million pixels, requiring 6 million bytes if we dump each of 
the red, green, and blue primaries with no image compression. Saving this 
as hexadecimal codes on paper would require 600 sheets of paper.

You don't want to store all that paper? Fine! Microfilm it. Microfilm has 
excellent longevity, and we don't care if it fades, so long as we can 
still read the characters on the pages.

Now, obviously this scheme can be improved. If you compress the image in
high-quality JPEG mode, you can reduce the size to 20 percent or less. 
You could also abandon the very inefficient hex code dump and save,
instead, graphic images of 24 bit planes representing your 24-bit color
image; and once again it won't matter if the images fade, because they
will be binary--black or white, on or off. 

Still, these schemes all entail some encoding. I'm willing to bet that
hexadecimal representation of byte values will still be understood 200
years from now, and provided you remember also to save a note of the
number of pixels per row in your image (!) the image will be reproducible
any time in the foreseeable future. 

Whether you will be there to see it, of course, is another matter.

--CP

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