From help-octave-request at bevo dot che dot wisc dot edu Sat Dec 21 00:20:41 2002
Subject: Re: octave and image processing
From: Andy Adler <adler at site dot uottawa dot ca>
To: "John W. Eaton" <jwe at bevo dot che dot wisc dot edu>
cc: Al Niessner <Al dot Niessner at jpl dot nasa dot gov>, <help-octave@bevo.che.wisc.edu>
Date: Sat, 21 Dec 2002 01:17:08 -0500 (EST)

On Fri, 20 Dec 2002, John W. Eaton wrote:
> On 19-Dec-2002, Al Niessner <Al dot Niessner at jpl dot nasa dot gov> wrote:
>
> | How can/should octave be changed to allow for processing very large
> | images?
>
> What do you want to be able to do with the image object?
>
> If you are looking for arbitrary numerical operations on images, then
> I don't see how you will be able to work on them without a lot of
> memory since you will probably want to use double precision
> arithmetic.  Even if single precision is good enough for image
> manipulation, I'm not sure that you will be able to get that in
> Octave, since I think it would be difficult to support both double and
> float arithmetic in Octave.
>
> If you don't need arbitrary numerical operations, then perhaps it
> would help to have int/short/char size matrix objects that can be used
> to store data?  I'm not sure what operations would be useful for these
> objects.  Would we want integer arithmetic rules, or conversion to
> double?
>
> I do think it would be useful for Octave to be able to do more things
> with images and for those operations to use less memory, but I'm
> curious to know why you don't simply use something that is already
> designed for image manipulation (the Gimp?).

I also do lots of image processing with octave. I research medical
image processing algorithms; for developing new image procesing
algorithms, tools like gimp are inappropriate. Until recently,
however, I didn't need to handle very large images - I see myself
doing this fairly soon, now.

I think that two additions would be very useful:

- support for short/char size matrix objects. This would be
  primarily to load images. Subsequent processing would
  then be done on subsections of the image in double precision.

- support for large matrices mapped to disk. The idea of
  Paul Kienzle to unify this with parallel processing support
  is excellent.

I'll try to put together some support for byte matrices as a test
of the first idea. Does anyone who has used the corresponding
feature in Matlab want to comment on the requirements?

My idea is to allow the result to be upcast to double whenever
an operation could potentially overflow.

andy





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