[vtkusers] Fast conversion from vtkImageData to QImage?

[Michael Jackson]

   The only way faster would be to try and work with the raw pointers  
for both the vtkImageData and the QImage. You do lose lots of safety  
checks, but from my experience calls like scalars- 
 >GetTupleValue(tupleIndex++, tuple); take longer due to the bounds  
checking (which is good) but if you feel you can get along without the  
bounds checking (because you already have checked) you can do it that  
way.
   BUT before doing ANYTHING, I would put some timing code in there so  
you can MEASURE the current performance and properly figure out where  
the bottleneck truly lies. Each platform has their own set of tools to  
do this. On OS X there is "Shark" and "Instruments" that can help show  
where the slow parts of your code are. Visual Studio and Linux both  
have tools also.

  "Premature optimization is the root of all evil"

_________________________________________________________
Mike Jackson                  mike.jackson at bluequartz.net
BlueQuartz Software                    www.bluequartz.net
Principal Software Engineer                  Dayton, Ohio

On Jan 29, 2010, at 6:09 AM, Prashanth Udupa wrote:

> Hi All,
>
> I have an application where I need to convert vtkImageData to  
> QImage. I am using the following code for this.
>
> Assumptions: vtkImageData is 2D. dim[0] is width, dim[1] is height.  
> Scalars associated with the image is always VTK_UNSIGNED_CHAR type.
>
> QImage ConvertToQImage(vtkImageData* imageData)
> {
>     int dim[3];
>     imageData->GetDimensions(dim);
>     if(dim[0]*dim[1]*dim[2] == 0)
>         return QImage();
>
>     vtkUnsignedCharArray* scalars
>         = vtkUnsignedCharArray::SafeDownCast(imageData- 
> >GetPointData()->GetScalars());
>     if(!scalars)
>         return QImage();
>
>     QImage qImage(dim[0], dim[1], QImage::Format_ARGB32);
>     vtkIdType tupleIndex=0;
>     unsigned char tuple[] = {0, 0, 0, 0};
>
>     for(int j=0; j<dim[1]; j++)
>     {
>         for(int i=0; i<dim[0]; i++)
>         {
>             int r=0, g=0, b=0, a=0;
>             scalars->GetTupleValue(tupleIndex++, tuple);
>
>             switch(scalars->GetNumberOfComponents())
>             {
>             case 1:
>                 r = g = b = tuple[0];
>                 a = 255;
>                 break;
>             case 2:
>                 r = g = b = tuple[0];
>                 a = tuple[1];
>                 break;
>             case 3:
>                 r = tuple[0];
>                 g = tuple[1];
>                 b = tuple[2];
>                 a = 255;
>                 break;
>             case 4:
>                 r = tuple[0];
>                 g = tuple[1];
>                 b = tuple[2];
>                 a = tuple[3];
>                 break;
>             }
>
>             QRgb color = qRgba(r, g, b, a);
>             qImage.setPixel(i, j, color);
>         }
>     }
>
>     return qImage;
> }
>
> I was wondering if there was a faster way to do this. If anyone has  
> hints for me, please do share.
>
> Thanks very much.
>
> Regards,
> Prashanth N Udupa
>
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