[Insight-developers] performance of image iterators and pixel buffer storage

[Dan Mueller]

Hi David,

I had just assumed you were meaning itk::Image::SetDirection(..)...
Sorry if I caused any confusion.

Regards, Dan

2008/11/4 David Fuentes <fuentesdt at gmail.com>:
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> Luis, Dan,
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> Thank you very much for clarifying this for me!
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> David
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> On Tue, 4 Nov 2008, Luis Ibanez wrote:
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>>
>> Hi David,
>>
>>
>> If by "SetDirection()" you are referring to the methods
>> in the Line Iterator and the Slice Iterator, then: Yes.
>> The order will impact your  performance.
>>
>>
>> If you were referring to the "image::SetDirection()" method,
>> then: No. The direction cosines of the image will not impact
>> the iterators performance, as Dan pointed out.
>>
>>
>> When you set a line iterator to walk along the direction "1"
>> instead of the direction "0", it will take longer to go through
>> the image.
>>
>>
>> If your algorithm give you the option of walking an image in
>> one direction  or another then you should select the "0" first.
>>
>>
>>  Regards,
>>
>>
>>     Luis
>>
>>
>> ---------------------
>> David Fuentes wrote:
>>>
>>> Dan, Thank you very much for the reply.
>>>
>>>> See the documentation in itkImage.h:
>>>>
>>>> * The data in an image is arranged in a 1D array as
>>>> [][][][slice][row][col]
>>>> * with the column index varying most rapidly.  The Index type reverses
>>>> * the order so that with Index[0] = col, Index[1] = row, Index[2] =
>>>> slice,
>>>> * ...
>>>>
>>>>> which value for
>>>>>
>>>>>  SetDirection()
>>>>>
>>>>> should be used to give the best performance?
>>>>
>>>>
>>>> From my understanding, SetDirection(..) has no impact on iterator
>>>> performance. SetDirection(..) changes the direction cosines, which are
>>>> used by TransformPhysicalPointToIndex(..),
>>>> TransformContinuousIndexToPhysicalPoint(..), and others in
>>>> itk::OrientatedImage (although in ITK 3.10, which is about to be
>>>> released, the direction cosines can be used in itk::Image, deprecating
>>>> itk::OrientatedImage).
>>>>
>>>
>>>
>>> A little confused.
>>> B/C of the memory storage setup, wouldn't you expect a significant cache
>>> performance difference if you iterate over row's vs iterating over
>>> columns?
>>> Are you saying that ITK iterators have some special abstraction to avoid
>>> this?
>>>
>>>
>>>
>>> df
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>>> Insight-developers at itk.org
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>>>
>>
>