[Insight-users] What is the *correct* way to downsample an image with ITK?

[poireau]

Xiaofeng Z wrote:
> 
> Let me get the question right.  You started with a uniform image and down
> sampled it.  The image the URL point to is the down sampled image,
> correct?
> What is the size of the downsized image?  What software do you use to see
> the checkerboard?  Could the alias a result of the view software?
> 

Hi Xiaofeng,

No, I started with the checkerboard image I linked to (try to view it with a
decent program, such as vv or even gimp), and tried downsampling it with
several different methods. Using a checkerboard pattern is a good way to
test a resampling algorithm, because it has a lot of high frequences.

The aliasing I observe is not a result of the software I use, as I have
studied the values of the individual pixels of the output image.

My conclusion is that you indeed need a low-pass filter before you
downsample an image. While a Gaussian filter may be OK if you want a
scale-space representation, it is clearly not the best when what you want is
an approximation of the original image at a lower resolution. However, since
ITK doesn't seem to provide the adequate filters, I think I will have to go
with the Gaussian for the time being. 
http://www.google.fr/url?sa=t&source=web&cd=1&ved=0CBcQFjAA&url=http%3A%2F%2Fwww.worldserver.com%2Fturk%2Fcomputergraphics%2FResamplingFilters.pdf&ei=ad0VTKSXFtGT4gb6od3IDA&usg=AFQjCNErH2yYYjbTVImVBeDM16blDdsL1w
This article , by a guy working for Apple, seems to have a couple answers on
the problem.
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