[vtkusers] Rotating image data

[David Gobbi]

I'd better add an errata to what I wrote:

3) Each (x,y,z) point is transformed by the ResliceAxes matrix, and
then the ResliceTransform, in that order.

I had the two operations reversed.

   David


On Fri, Jul 9, 2010 at 8:21 AM, David Gobbi <david.gobbi at gmail.com> wrote:
> 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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>>>
>>>
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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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