[vtkusers] How to get the pixels of a volume rendered image?

[Wilf Rosenbaum]

Hi Sankhesh,
  Thanks so much! I tried your suggestion and it worked just fine. I really
appreciate you taking the time to answer my question.
Cheers,
Wilf.

On Mon, Mar 20, 2017 at 1:47 PM, Sankhesh Jhaveri <
sankhesh.jhaveri at kitware.com> wrote:

> Hello Wilf,
>
> If you use the vtkGPUVolumeRayCastMapper, you can enable the RenderToImage
> mode that basically renders the volume to an OpenGL FrameBufferObject. It
> then has API like GetColorImage() and GetDepthImage() to get the color
> and depth data of the rendered result.
>
> Hope this helps.
>
> Thanks,
> Sankhesh
> ​
>
> On Mon, Mar 20, 2017 at 11:36 AM Wilf Rosenbaum <wilf.rosenbaum at gmail.com>
> wrote:
>
>> Hi Guys,
>>   VTK noob here. Ignorant, but (hopefully) not stoopid.
>>
>>   I am interested in creating a volume rendering (VR) of a volumetric
>> medical (CT) dataset, and then getting access to the pixel values of that
>> volume rendering image. I can follow along with the SmartVolumeMapper
>> example from the VTK examples website, which creates the VR for my dataset
>> but displays the result in a vtkRenderWindow. Right now I don't want to
>> display the VR image, I just want to get the pixel values and do something
>> with them - pass them to a 3rd party program for instance. I understand
>> that I could use a vtkWindowToImageFilter to convert the data in my
>> RenderWindow to an image, but intuitively this seems like a rather
>> circuitous route to get what I want. I suspect that there is a more direct
>> standard vtk workflow.
>>
>>   I know that if I was interested in an orthogonal or an oblique slab
>> through my volume I can create a pipeline like
>>
>>      vtkDicomImageReader -> vtkImageReslice -> vtkImageMapToColors
>>
>> and then call GetOutput() -> GetScalarPointer() on the
>> vtkImageMapToColors object to get the pixels of the slab - no RenderWindow
>> is required. Is there something analogous for volume rendering?
>>
>> If the real answer to my question is "create a hidden render window,
>> render the volume into that hidden render window and then use a Window to
>> Image Filter to get the image" then I am fine with that but I feel like I
>> don't know enough about VTK yet to know for sure.
>>
>> Finally, please free to suggest some terms to google. I am happy to do
>> more research, but I feel like I need to be pointed in the right direction.
>> I am already looking into "vtk render to frame buffer" , "vtk render to
>> image", "vtk offscreen rendering", ...
>>
>> Thanks very much!
>> Cheers,
>> Wilf
>>
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> --
> Sankhesh Jhaveri *Sr. Research & Development Engineer* | Kitware
> <http://www.kitware.com/> | (518) 881-4417
> ​
>
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