RE: Help with matrix replication

[Richardson, Anthony]

> On Behalf Of Carnë Draug
> > Subject: Help with matrix replication
> >
> > By the way, imresize(a, 2, 'nearest') will do what I want, but this is a
> function from the image package and I'm trying to write some routines that
> duplicate the functionality of the image package without using any of those
> functions.
> 
> Why are you avoiding the image package? It's the second time this week
> someone tries to solve something that is already on a package but does not
> want to use it. I don't understand the aversion.
> 
> You know that you can at least just look into imresize, see how it works and
> use it.

I'm not averse to using it.  I'm using it a lot, but I'm also studying image 
processing and most of the study involves implementing many image processing 
algorithms in Octave.  Most (all?) of the algorithms are already implemented in 
the image package.  We aren't allowed to use routines from the image package 
except to compare the results from our routines to those from the image package.

Also, imresize appears to fit the image matrix to a grid and then uses one of 
several different interpolation methods (user selectable) to generate a new 
(larger or smaller) image matrix.  I'm interested only in the specific case of 
generating a larger matrix by pixel replication (at this point) and thought 
that clever indexing might provide a "better" solution than the more general 
interpolation method used by imresize.  That appears to be the case.  On my 
machine resizing a 2x3 double matrix by a factor of 1000 using indexing is over 
50 times faster than using imresize.  Also, I can increase the same matrix by a 
factor of 5000 using indexing, but get a "memory exhausted" error when using 
imresize with a factor of 2000.  (I'm not complaining about imresize.  It is 
great, but it might not be the best method to use when you are interested only 
in pixel replication.)

Tony