[Insight-users] A Few Questions and Problems

[Karthik Krishnan]

Hi Amitesh,

I agree with Jens: opening is erode followed by dilate. Maybe I am mistaken.

As far as noise removal and minimum erosion followed by maximum dilation.

While erosion can be used to eliminate small clumps and salt noise, it 
has the big disadvantage that it will affect// all foreground pixels 
indiscriminately. Opening gets around this by performing both an erosion 
and a dilation on the image.

If you use Binary dilate with minimum erosion and maximum dilation, ie 
different sized structuring elements, idempotency is lost (ie further 
opertations of opening on the same image will start having an effect 
closer to dilation rather than have no effect). Some regions will start 
merging with each other.

Maybe I am missing the point.

thanks
karthik

Amitesh Agarwal wrote:

>Hi Jens,
>
>Well if you refer to the book "Digital Image Processing" by Rafeal C.
>Gonzalez & Richard E. Woods Section 9.2 & 9.3 specifically 9.3 It says
>"Dilation expands an image and erosion shrinks it ........ Opening
>Generally Smoothes the contour of an object, breaks narrow isthumuses
>and eliminates thin protrusion. Closing also tends to smooth sections
>of countour, as opposed to opening, it generally fuses narrow breaks
>and long thin gulfs, eliminates small holes, and fills gaps in the
>countour"
>
>Moreover in certain situtations, as I have experienced while working
>with binary image of skull and brain,  a combination of BinaryErode
>and BinaryDilate doesn't completly solve the problem of opening and
>closing in some regions. Some regions actually start merging with each
>other if I use a bigger BinaryStructuralBallBearingElement (5x5x5) for
>better removal of undesirable noise in the data in the order first
>BinaryErode and then BinaryDilate with minimum erosion and maximum
>dilation for best results.
>
>I hope this clarifies my point.
>
>Amitesh
>
>
>On Wed, 5 Jan 2005 08:47:04 +0100, Jens Eickmeyer <eickmeyer at gmail.com> wrote:
>  
>
>>Hi!
>>
>>On Tue, 4 Jan 2005 15:40:43 -0600, Amitesh Agarwal
>><amiteshagarwal at gmail.com> wrote:
>>    
>>
>>>4) Opening and closing operation in a binary image
>>>
>>>I just wanted to know if there is any filter present in ITK for
>>>performing opening and closing operation in a given Binary Image. It
>>>is my understanding that BinaryErode and BinaryDilate do similar
>>>operation in effect but not exactly the same.
>>>      
>>>
>>I haven't found such a filter, too. I use BinaryDilate and BinaryErode
>>to apply closing to a binary image. But why are you thinking that this
>>hasn't the same effect? Closing is just a dilation followed by am
>>erosion and opening is just an erosion followed by a dilation. If
>>BinaryErode and BinaryDilate work correctly - and I think we can
>>assume this - the combined execution should lead to the right results.
>>
>>Jens
>>
>>    
>>
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>

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