[vtkusers] vtkImageReslice speed

[David Gobbi]

alex. gouaillard wrote:
> On Sun, 2006-03-26 at 02:15, David Gobbi wrote:
>   
>> Hi Lyubomir,
>>
>> There is nothing special about the number "256" in vtkImageReslice,
>> so the loss of performance is probably due to a secondary issue.
>>
>> For example, if you are using vtkImageActor or vtkImagePlaneWidget
>> to display the image, note that the size of the OpenGL texture is
>> always
>> a power of two, so an image that is 257 pixels on a side will be
>> displayed
>> on a texture that is 512 pixels on a side.
>>     
>
> well, OpenGl has been handling non power of two textures for several
> years already (see
> http://oss.sgi.com/projects/ogl-sample/registry/ARB/texture_non_power_of_two.txt). Depending on your implementation of OpenGl that is more or less supported, but I assume Mesa would. Is there any reason why this happen in VTK (i.e. is it hard-coded?).
>   
Until very recently, VTK strictly followed the OpenGL 1.1 standard and 
used no extensions.  The reason for this was maintenance and testing, 
particularly on Windows since Microsoft only guarantees conformance with 
OpenGL 1.1.  As soon as new code paths are put in to take advantage of 
OpenGL extensions that may or may not be present on a system, you have 
to run tests both on machines that have the extensions, and on ones that 
don't.

I suspect that Kitware is more open to allowing OpenGL extensions now 
than they were before, and speaking for myself, I think this would be a 
great addition to vtkOpenGLTexture.

 - David


> alex
>
>   
>>  - David
>>
>>
>> ----- Original Message ----
>> From: Lyubomir Zagorchev <lzagorch at verizon.net>
>> To: vtkusers at vtk.org
>> Sent: Saturday, March 25, 2006 11:45:15 AM
>> Subject: [vtkusers] vtkImageReslice speed
>>
>> I am using vtkImageReslice to cut three orthogonal cross sections from
>> a volume.
>> I noticed that if the volume has axial dimensions greater than 256 the
>> performance 
>> of the filter becomes very slow ( even if the axial dimensions are
>> 257, the speed
>> decreases significantly). Could someone briefly explain what is the
>> reason for 
>> that? Can I do something in my code that will increase the speed of
>> the filter?
>>  
>> Thank you,
>>  
>> Lyubomir 
>>  
>>     
>
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