[vtkusers] Real-Time Image Warping

[Jorge Ballesteros]

Hi David,

As you indicated I have rescaled the image to 256x256x98 and the 
performance is better. For an 256x256x3 input image the warping frame 
rate is about 25Hz.

Even though is a big improve, i would like to keep on improving the 
performance, but not downsampling the image. I am using 
vtkThinPlateTransform as the the input to a vtkTransformToGrid and then 
using a vtkGridTransform as the reslice transform to the vtkImageReslice 
filter. I have been trying several pipelines but this is the one that 
returns the best results. Not sure if these are the proper functions to 
perform a 3D image warp. Am i right? Below is an extract of the code:

vtkSmartPointer< vtkDICOMImageReader> reader = 
vtkSmartPointer<vtkDICOMImageReader>::New();
    reader->SetDirectoryName(argv[1]);
    reader->Update();

vtkImageData * input = reader->GetOutput(); //256x256x3

Downsampling...

double point[3];
double target[3];
...

int limit = 15;

    vtkSmartPointer< vtkPoints > p1 = vtkSmartPointer< vtkPoints >::New();
    p1->InsertNextPoint(point[0]-limit, point[1], point[2]);
    p1->InsertNextPoint(point[0], point[1]+limit, point[2]);
    p1->InsertNextPoint(point[0]+limit, point[1], point[2]);
    p1->InsertNextPoint(point[0], point[1]+limit, point[2]);
    p1->InsertNextPoint(point[0]-limit, point[1]-limit, point[2]);
    p1->InsertNextPoint(point[0]-limit, point[1]+limit, point[2]);
    p1->InsertNextPoint(point[0]+limit, point[1]-limit, point[2]);
    p1->InsertNextPoint(point[0]+limit, point[1]+limit, point[2]);
    p1->InsertNextPoint(point[0], point[1], point[2]);

    vtkSmartPointer< vtkPoints > p2 = vtkSmartPointer< vtkPoints >::New();
    p2->InsertNextPoint(point[0]-limit, point[1], point[2]);
    p2->InsertNextPoint(point[0], point[1]+limit, point[2]);
    p2->InsertNextPoint(point[0]+limit, point[1], point[2]);
    p2->InsertNextPoint(point[0], point[1]+limit, point[2]);
    p2->InsertNextPoint(point[0]-limit, point[1]-limit, point[2]);
    p2->InsertNextPoint(point[0]-limit, point[1]+limit, point[2]);
    p2->InsertNextPoint(point[0]+limit, point[1]-limit, point[2]);
    p2->InsertNextPoint(point[0]+limit, point[1]+limit, point[2]);
    p2->InsertNextPoint(target[0], target[1], target[2]);


    vtkSmartPointer< vtkThinPlateSplineTransform> transform = 
vtkSmartPointer< vtkThinPlateSplineTransform>::New();
    transform->SetSourceLandmarks(p1);
    transform->SetTargetLandmarks(p2);
    transform->SetBasisToR();

    //Convert the thin plate spline to a grid
    vtkSmartPointer<vtkTransformToGrid> transformToGrid = 
vtkSmartPointer<vtkTransformToGrid>::New();
    transformToGrid->SetInput(transform);
    transformToGrid->SetGridExtent(-2*limit, 2*limit, -2*limit, 2*limit, 
0, 0);
    transformToGrid->SetGridOrigin(point);
    transformToGrid->SetGridSpacing(input->GetSpacing());
    transformToGrid->SetGridScalarTypeToShort();

    vtkSmartPointer<vtkGridTransform> gridTransform = 
vtkSmartPointer<vtkGridTransform>::New();
    gridTransform->SetDisplacementGrid(transformToGrid->GetOutput());
    
gridTransform->SetDisplacementShift(transformToGrid->GetDisplacementShift());
    
gridTransform->SetDisplacementScale(transformToGrid->GetDisplacementScale());

    vtkSmartPointer< vtkImageReslice > reslice = 
vtkSmartPointer<vtkImageReslice >::New();
    reslice->SetInput(input);
    reslice->WrapOn();
    reslice->SetResliceTransform(gridTransform);
    reslice->SetInterpolationModeToLinear();
    reslice->SetOutputSpacing(input->GetSpacing());
    reslice->SetOutputExtent(0, 255, 0, 255, 0, 2);
    reslice->Update();

Thanks for your support,

Jorge.


David Gobbi wrote:
> Hi Jorge,
>
> For real-time image warping in VTK, you would probably have to go with
> 256x256 images in order to achieve the 10Hz goal that you are aiming
> for.  For warping a 512x512x100 volume in real time, I think your only
> option would be to use the GPU.
>
>    David
>
>
> On Thu, Apr 8, 2010 at 4:38 AM, Jorge Ballesteros
> <jballesteros at motivando.me> wrote:
>   
>> Hello all,
>>
>> I have been trying to perform a real-time image warping with no success.  I
>> have managed to warp a 512x512x100 Image but the computation time it takes
>> is very high. Then I extracted a portion of the image, just 3 slices and
>> warped the image but still don't meet real-time requirements.
>>
>> FYI i have been following VTK Examples, Hybrid/Testing/TestGridWarp3d.tcl,
>> using the vtkImageReslice class with a vtkGridTransform as the input
>> transform and a 512x512x3 input image, obtaining a ~10 Hz frame rate.
>>
>> Don't know if there is any other way on doing this. It would be really
>> helpful if you could point me on how to achieve it.
>>
>> Thanks,
>>
>> Jorge
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