[vtkusers] Fast element access of vtkImageData?

[Joseph D. Wieber Jr.]

Hi Dominique,

Thanks for your response.  What should I expect from 
GetScalarPointer()?  For example, if I have a vtkImageData object with 
four float components (say RGBA), should I expect to be able to cast the 
void* to float* and have it point to an array of four floats?  I 
modified my template to the below, but it didn't work.  Am I expecting 
the wrong return?

     //ImageDataPtr is: typedef vtkSmartPointer< vtkImageData > 
ImageDataPtr;

     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 )
                 {
                     T* ptr = static_cast< T* >( 
pImageData->GetScalarPointer (x, y, z) );

                     for( int c = 0; c < numComponents; ++c )
                     {
                         *ptr = val;  //*ptr++ = val;
                         ++ptr;
                     }
                 }
             }
         }
     }

Thanks again.

Regards,
Joseph


On 07/27/2011 04:22 PM, Dominique Töpfer wrote:
> 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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