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Re: image.m and scaling


From: Robert A. Macy
Subject: Re: image.m and scaling
Date: Fri, 03 Jun 2005 17:41:31 -0700

Brian,

After initiating octave, at the prompt I typed in...

>> imagesc(rand(20));

...and got a small window that looked like WindowsExplorer
showing my home directory.


The other lines give an error that zoom is undefined.
          running 2.1.50a on win98
too old?  

What were those lines supposed to do?


I've never used the image commands, but once I had a need
to expand a very coarse matrix for better viewing.  The
matix was 7 x 7 and too coarse to even begin to see a
pattern.  

I wrote a small function that doubled the array size to
make better presentations.  Actually 2x-1 each side.

first attempt Rules:  
every data point is preserved.  
values between points is the average of adjacent points 
This produced "rampy" displays

a little smoothing helps...
second complicated rules:
ON index (use 3 points)
BETWEEN index (use 4 points)
EDGES preserved by "tapering" effect

Produced "filled" in displays and patterns were very easy
to see.  

Is this what you need? 
 
           - Robert -


On Fri, 03 Jun 2005 17:59:28 -0400
 Brian Blais <address@hidden> wrote:
> Hello,
> 
> I was wondering what others thought of the following
> observation.  When
> I do an image command, or an imagesc command, the
> resulting image is
> increased in size (IMHO, good) and smoothed (IMHO, bad).
>  Usually when I
> am looking at a small matrix, I am looking at data and
> would like to see
> an honest representation of those data points, more
> similar to matlab's
> image command.  If one changes one word in image.m from:
> 
> im_display = sprintf ("display -geometry %f%% \"%s\"",
> zoom*100, ppm_name);
> 
> to:
> 
> im_display = sprintf ("display -sample %f%% \"%s\"",
> zoom*100, ppm_name);
> 
> using the -sample option, then you get the same increase
> in size, which
> is good for visibility, and the image is not smoothed.
>  Try it with:
> 
> imagesc(rand(20));
> 
> and you'll see the difference.  Is this something that
> others would
> like, or is the present behavior there for some reason?
> 
> 
>                       thanks,
> 
>                               Brian Blais
> 
> 
> -- 
> -----------------
> 
>              address@hidden
>              http://web.bryant.edu/~bblais
> 



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