Subject: Re: Second summary of Image Standard for Space Shuttle Program

From: dbriggs at zia.aoc.nrao.edu (Daniel Briggs)
Date: 22 Aug 91 16:30:59 GMT

In article <1991Aug20.050605.324 at aio.jsc.nasa.gov> kjenks at galileo.uucp
(Kenneth C. Jenks [GM2] 483-4368) writes:
>The story so far:
>
>I'm in the Space Shuttle Program Office (Level II), in the
>Management Integration/Information Systems Office at JSC.  My
>office sets information systems standards for the Space Shuttle
>Program.  My boss asked me to put together a draft of a photo
>transmission and storage standard.  
>
>I proposed to the Internet that I was going to make the Shuttle program
>standardize on GIF as the image file storage and interchange format.
>Everybody said no, so I changed by mind and proposed TIFF 5.0.  The
>plan is to impose an interim standard now, then move all our files to
>the official US Gov't standard when it comes out.

I don't flame in public that often, but this is above and beyond....

I didn't reply to your original post because *I THOUGHT IT WAS A JOKE*!

I simply couldn't believe that a) someone would possibly suggest using
GIF as a serious format for interchange of even semi-scientific data
and that b) someone would, in the same message, suggest that this
decision would have serious implications across the entire US space
program, ask questions of a level indicating that essentially *no*
background research has been done ("What are the advantages and
disadvantages of GIF vs. the other color image standards?") and
propose as the standard the single format about which he had
(incomplete) information.

Look, Ken, I'm happy that you've decided to let the net in on an
important decision, and Usenet is a valuable resource for something
like this.  But we are NOT here to do your job for you.  If you look
at your original post, it has more in common with the posts that
begin, "I'm doing a report for my high school science class.  Please
send me all the information you have on the space shuttle." than it
does with a serious scientific proposal.

The next thing you should realize is that while the network is a
useful way to gather large numbers of opinions, it is probably not a
representative sample of the people you need to ask.  If you ask a
teenage hacker with a C64 what image standard he wants you to use, he
will likely tell you GIF or TIFF.  If you ask a researcher at a
scientific institution, she will likely tell you something else.  So
the first question on your list should be "what is the user population
for my standard, and what are their needs?"  I don't know the answer
to that question, so it's hard to suggest an answer to your original
post.  I strongly suspect that you will have at least two
fundamentally different populations of users, and that their desires
will be different and possibly even incompatible.

The scientific community *must* have an imaging standard with header
information.  At a minimum, it must specify such information as how
the axes of the image correspond to real world coordinates on the sky
or on the earth.  It must specify the observing wavelength(s).  It
should specify when the data was taken, by whom, and with what
instrument.  It might include history information on how the data was
processed, (eg. clipping, transformations and deconvolution).  It
might include auxiliary tabular information such as filter
characteristics or gain information.  I'll admit that I'm personally
partial to FITS as a common standard that does all this and more, but
essentially any well thought out scientific standard that preserves
this information would do.  If you go with GIF or TIFF, you'll have to
have some sort of auxiliary header file which will of course need its
own standard.  Two files instead of one then carries the risk that
they can become separated or modified relative to each other.  Better
just to do it right in the first place.

On the other hand, the more complete formats are complicated.  FITS
readers are just now starting to appear for PC class machines, and
aren't exactly common.  (It's probably even worse for the other
scientific imaging standards.)  FITS itself isn't really an ideal
format for the transmission of simple color images.  It essentially
deals with the problem of getting arbitrary numbers into arbitrary
shaped arrays on the target machine, and leaves the problem of display
to the target.  I don't believe that there is a generally accepted
substandard on color table mappings, for instance.  (If I am wrong on
this, someone please tell me?)  While it would certainly be trivial to
put the three RGB planes on the third axis of the data cube, I'm not
even sure if that is standardized.  You might want to get in touch
with STScI, to see if they've adopted any standard for "general
release" images.  Our local FITS guru is Don Wells, (dwells at nrao.edu),
and I'm sure he'd be willing to answer questions if you explained your
situation.  Also, it's true that FITS is not a compressed format.  To
some extent, this can be alleviated with external compressors, but
that's still a pain.  A compressed FITS standard is in the works, but
don't expect it anytime soon.

It really looks to me like you're going to be stuck with two
standards: an internal one for people who need to work with the
images, and an external one for the people who simply want to look at
the pictures.  If you've got to have one single format, I think the
external users lose, since they can go to the more complicated
formats, while the scientists simply cannot put back data that has
been thrown away.

>I'm writing a position paper this week.  I'll post a draft to the net
>for comments.

While I question that you're really ready to write a position paper this
week, please do post what ever you come up with on the net.  You might
seriously think about using that week in email and phone discussions with
the people who are most likely to use your images, though.

-- 
Daniel Briggs  (dbriggs at nrao.edu)
New Mexico Tech / National Radio Astronomy Observatory
P.O. Box O / Socorro, NM 87801   (505) 835-7391