Re: opening and display large file

[Craig Markwardt <craigmnet(at)cow.physics.wisc.edu>]

Sylvain Carette <sylvainc@total.net> writes:

> Hi
> How do you manage to display very large images? What is the options?
> From the manual, it seem that using "assoc" is a winner but maybe with
> one little example it would be more clear how can this be (It seem to me
> that it is an important aspect of programming with IDL since most of the
> time you'll deal with larger than memory files).
> Even with assoc, dont you still have to copy from the file to an array
> before display?
> I dont decipher exactly why and when to use readu or read_binary, the
> file pointer, assoc or writing to an offscreen buffer.

What you are hearing from people is that you definitely need to do
some kind of chunking, banding, tiling, whatever you want to call it.
This involves only reading a subset of the image at a time, and
operating on it.  For example, I know of no display that can handle
4800x6000 resolution, so you will probably only want to look at
subsets.

ENVI and/or FREELOOK is probably the commercial version of doing this,
since it's specifically designed for large images.

Doing it on your own is not necessarily hard, but it will take some
experimenting to do it right.

Craig

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Craig B. Markwardt, Ph.D.         EMAIL:    craigmnet@cow.physics.wisc.edu
Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
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