[vtkusers] Fast element access of vtkImageData?

[Dominique Töpfer]

Hi Joseph,

you could use GetScalarPointer(), which gives you a void * pointer to 
the actual image data. After casting it to the pixel type you are using, 
you can access the array directly, which should be much faster. To 
access a certain point you could use ComputePointID() to get the correct 
index.

HTH
Dominique

On 27.07.2011 22:07, Joseph D. Wieber Jr. wrote:
>
> Hello,
>
> Is there a fast way to access (get and set) elements in a vtkImageData 
> object?  For instance I have two image data object with dimensions 
> 512x512x1 that I'm using as part of a cost table (it's convenient) for 
> an algorithm.  One of them gets the output of a convolution filter and 
> I do lookups into it.  The other one has to be initialized to all 1.0 
> values at the beginning of the algorithm.  Then based on information 
> from the first one, I set values in the second one.  The algorithm is 
> a specialized Laplacian zero crossing.  I've been using the following 
> template to initialize all the values to 1.0:
>
> //----------------------------------------------------------------------------- 
>
> //TODO: This is horribly slow.  Find a smarter way!
>
> template< typename T >
> void
> fillImageData(  ImageDataPtr pImageData, const T& val )
> {
>     int dims[ 3 ];
>     pImageData->GetDimensions ( dims );
>     int& xMax = dims[ 0 ];
>     int& yMax = dims[ 1 ];
>     int& zMax = dims[ 2 ];
>     int numComponents = pImageData->GetNumberOfScalarComponents ();
>
>     for( int z = 0; z < zMax; ++z )
>     {
>         for ( int y = 0; y < yMax; ++y )
>         {
>             for( int x = 0; x < xMax; ++x )
>             {
>                 for( int c = 0; c < numComponents; ++c )
>                 {
>                     pImageData->SetScalarComponentFromFloat ( x, y, z, 
> c, val );
>                 }
>             }
>         }
>     }
> }
>
> To get and set values during the zero crossing computation I've been 
> using combinations of GetScalarComponentAsFloat, and 
> SetScalarComponentFromFloat and this part is also very slow.
>
> Can someone please point me to an example that accomplishes similar 
> tasks in a more efficient manner, or offer a suggestion on where to 
> look?  Thank you.
>
> Regards,
>
> Joseph
>
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