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Re: Importing a large image...

  • To: mathgroup at smc.vnet.net
  • Subject: [mg98595] Re: Importing a large image...
  • From: Szabolcs Horvát <szhorvat at gmail.com>
  • Date: Mon, 13 Apr 2009 03:37:23 -0400 (EDT)
  • References: <grpiih$lqm$1@smc.vnet.net>

David Reiss wrote:
> So, my fellow denizens of the group.
> 
> I have a very large TIFF image--roughly 700MB in size.
> 
> Its dimension are 43201 by 15601.  It is single color with a bit depth
> of 8.
> 
> Mathematica is unable to Import this file on my 6 GM RAM powerbook
> without maxing out the memory.
> 
> I actually do not need to read in the whole file: I'd be happen with
> being able to break the file into a number of smaller TIFFs which tile
> it completely and then process each on independently (I am needing to
> act on the data in various ways to yield a processed result for
> further analysis down the line).   This is all for a larger project
> for a consulting client of mine.
> 
> Any suggestions for how to programmatically carve up the image without
> having to completely read it in first?   I am looking for quick
> solutions rather than ones that require a lot of programming.  Either
> it can be done pretty simply, or (more likely) Mathematica chokes on
> these very large files.
> 
> (Photoshop, on the other hand, does not choke on it at all, nor do
> some other programs that are optimized for image analysis such as ENVI
> (http://www.ittvis.com/ProductServices/ENVI.aspx): but I don't want to
> work with these...  nor do I have them....)

Naturally, Mathematica can't be good for any task.  Sometimes you have 
to use other programs too :)

So I'd recommend trying ImageMagick's convert tool:

http://www.imagemagick.org/

convert -crop 200x200 yourfile.tiff out%d.png

will break the image into 200x200 pixel tiles.  Now I can't guarantee 
that it won't run out of memory, and I did have trouble with the TIFF 
files ImageMagick generated in the past (that's why I used PNG as the 
output in the example), but it's certainly worth a try.

> 
> Of course this leads to a suggestion for the Import function: to allow
> reading in only a part of an image at a time.
> 
> Feel free to respond to the list, but also CC me on the replies so
> that I get them sooner than the usual turnaround.
> 



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