[vtkusers] Rotating image data

[David Gobbi]

Really, vtkImageReslice is the only straightforward way to rotate an
image in VTK.  It does change the pixel matrix, the basic job of
ImageReslice is to resample an image through a transform.

The operation of vtkImageReslice is like so:
1) The output Extent/Origin/Spacing of vtkImageReslice define an
output voxel grid.
2) Reslice loops through all output voxels, and computes the (x,y,z)
data coords for each voxel in turn.
3) Each (x,y,z) point is transformed by the ResliceTransform, and then
the ResliceAxes matrix, in that order.
4) The reslice's input data is interpolated at the transformed (x',y',z') point.
5) The interpolated value from the input at coordinate (x',y',z') is
used to set the value of the output voxel at (x,y,z).

Lots of people have trouble with (1).  Because vtkImageReslice isn't a
vtkProp it doesn't know anything about how it's output will be
displayed, it doesn't know how to properly set its own output voxel
grid.  So you should usually set the output Spacing/Origin/Extent
manually.  If you don't, then vtkImageReslice will try to "guess" what
a reasonable output grid would be, and it will usually guess wrong,
because it doesn't know anything about how the image will eventually
be displayed.

I've had a plan for a long time now to write a vtkProp3D based around
vtkImageReslice that will do all the mathematical trickery needed to
make VTK more friendly for 3D image display.  In my own image display
applications, I set up some low-level observers that keep track of the
camera position and the window size, and then have those observers set
the vtkImageReslice parameters so that the image displays exactly the
way that it should.

   David




On Fri, Jul 9, 2010 at 7:52 AM, Lic. José M. Rodriguez Bacallao
<jmrbcu at gmail.com> wrote:
> this may be a silly question:
> 1- which is the correct preffered way to rotate(transform) an image,
> with the camera or with vtkImageReslice?
> 2- does vtkImageReslice change/transform the pixel matrix?
>
>
> On Fri, Jul 9, 2010 at 7:34 AM, Jothy <jothybasu at gmail.com> wrote:
>> Some sort of padding befor rotation should help.
>>
>> Jothy
>>
>> On Fri, Jul 9, 2010 at 12:32 PM, Srinivasa Rao <srinivas at rsageventures.com>
>> wrote:
>>>
>>> Hi All,
>>>    I am trying to rotate vtkImageData using vtkTransform and
>>> vtkImageReslice, i used following code to do the job.
>>>
>>> vtkImageData * rotateImage(vtkImageData *data, QPointF center, int angle)
>>> {
>>>         vtkTransform *imageTransform = vtkTransform::New();
>>>         imageTransform->PostMultiply();
>>>         imageTransform->Translate(center.x(), center.y(), 0.0);
>>>         imageTransform->RotateZ(angle);
>>>        imageTransform->Translate(-center.x(), -center.y(), 0.0);
>>>         // Now create filter and set previously created transformation
>>>         vtkImageReslice *algo = vtkImageReslice::New();
>>>         algo->SetInput(data);
>>>         algo->SetInformationInput(data);
>>>         algo->SetResliceTransform(imageTransform);
>>>         algo->SetInterpolationModeToLinear();
>>>         algo->Update();
>>>         return algo->GetOutput();
>>> }
>>>
>>> When i try to rotate image data, after rotation the data which is outside
>>> the image is getting lost.
>>> Is there a way around to rotate image data without data loss..
>>> thanks in advance.
>>> regards,
>>> srinivas.
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>
>
>
> --
> Lic. José M. Rodriguez Bacallao
> Centro de Biofisica Medica
> -----------------------------------------------------------------
> Todos somos muy ignorantes, lo que ocurre es que no todos ignoramos lo mismo.
>
> Recuerda: El arca de Noe fue construida por aficionados, el titanic
> por profesionales
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