[Insight-users] Linear Vs Non-linear filters

[Luis Ibanez]

Hi Neha,

Your list of question will generate good material
for a course in image processing.

The ITK theory book "Insight into Images" that will
be published soon will certainly give you a good
overview of these concepts.

In the meantime here are some comments:

1) Yes, you should consider if a filter is linear
    or non-linear.  In practice, linear filter are
    only useful a preprocessing and postprocessing
    filters. They lack the capabilities for performing
    image analysis.

2) In a real application you will combine linear and
    non-linear filters. Most people in image processing
    is very pragmatic and will actually not care much
    about whether the filter is linear or not, as long
    as the filter contributes to produce the desired
    result.

3) There are not frequency domain filters in ITK at
    this point.  This will certainly change with the
    recent introduction of efficient FFT methods.

4) In practice, Segmentation is mostly a space-based
    activity rather than a frequency one. You could
    of course imagine cases in which pixel texture
    could contribute to define anatomical regions,
    and in such cases frequency-base analysis could
    help to enhance the delineation of such regions.

The current trend in medical image analysis points
more in the direction of creating models that contain
anatomical information. In that trend, frequency based
filters have only a secondary role, as preprocessing
enhancement filters.

In other words, if you are planning what book to buy
next, an "Anatomy Atlas" should be top on your list
before any other image processing book.



Regards,



     Luis



---------------
Neha D wrote:
> Hello All,
> 
> While applying filters for specific purpose, should we consider if that 
> filter is linear or non-linear. When to use linear and when to use 
> non-linear filter?
> 
> Also, among the filters in ITK, which are spatial filters and which one 
> are frequency domain filters.
> 
> What is more useful for medical images ? why ?
> 
> thanks,
> 
> neha
> 
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