[vtkusers] vtkImageActor and scaling

[David Gobbi]

On Tue, Nov 30, 2010 at 4:09 AM, endlosschleife1 <
endlosschleife1 at googlemail.com> wrote:


> that did it in combination with a reset on the camera after I get it from
> the renderer (otherwise  in my case the image was shifted partly out of the
> viewport). Thank you!
>

Instead of resetting the camera, you should directly set the camera Position
and FocalPoint. Set the FocalPoint to the center of your image, and then set
the Position so that it is some small distance away from the FocalPoint in
the direction of the image normal.


> What would be the equivalent if I would use a vtkActor2D?
>

There is no camera for vtkActor2D, they always use display coordinates
directly.  Instead of scaling a vtkImageMapper, you have to use
vtkImageReslice to resample the image at a higher or lower resolution.


> The possible reason to do that in my case is that the window level lookup
> table operation that I need in the vtkImageActor implementation seems to be
> very slow compared to when I set the window/level of the vtkImageMapper for
> a vtkActor2D (24ms slower per 512x512 image). I will need to look at that as
> well, since I assumed that the vtkImageMapper just uses the same lookup
> table operations, but that's a different story...
>

What are you using for window/level with vtkImageActor?  The typical way is
with a vtkLookupTable and vtkImageMapToColors (which can also map to
greyscale).

The vtkImageActor and the vtkImageMapper work completely differently.  The
more you expect them to behave similarly to one another, the more you will
confuse yourself.  Each is designed to utilize a completely different set of
GPU primitives.

  David


2010/11/29 David Gobbi <david.gobbi at gmail.com>
>
> Hi Mark,
>>
>> The camera method you want is SetParallelScale(), it sets the height of
>> viewport when ParallelProjection is on.
>>
>>   David
>>
>>   On Mon, Nov 29, 2010 at 8:24 AM, endlosschleife1 <
>> endlosschleife1 at googlemail.com> wrote:
>>
>>>   Hi all,
>>>
>>> I'm a bit confused about how cameras are initialized. I would like to
>>> scale a 2D image (scale a DICOM image to best fit a viewport size). I first
>>> did this via vtkImageResample and that works fine, but now I would like
>>> to try this with accelarated scaling and so I wanted to do that as part of
>>> the visualization pipeline (I hope that means that it is actually using
>>> OpenGL). I replaced my original vtkActor2D/vtkImageMapper with a
>>> vtkImageActor. The following works (pseudo code):
>>>
>>> Variant 1:
>>> - add imageActor to renderer, and renderer to renderwindow. Then call
>>> Render() on renderwindow.
>>> -> The image displays as expected in the original size.
>>>
>>> Variant 2:
>>> - same as in Variant 1 (including Render() call)
>>> - renderer->GetActiveCamera()->ParallelProjectionOn()
>>> - renderer->GetActiveCamera()->Zoom(zoomFactor);
>>> -> The image displays with the desired scaling.
>>>
>>> But variant 2 only works because I called Render() first. I assume this
>>> somehow initializes the camera of the renderer with exactly the attributes
>>> that I need, but when I call GetActiveCamera without rendering first this
>>> (just calling the getter-method) will already) will give a different result
>>> (in my case a grey box in the upper right corner of the viewport). I'm now
>>> about to reverse engineer the camera settings after variant 1 was executed
>>> and set all the camera attributes to the desired initial values (position,
>>> viewUp, clipping range etc.), but I'm wondering if I'm just missing the more
>>> appropriate and convenient way to do this (after all the vtkImageActor seems
>>> to be all about convenience).
>>>
>>> Thank you.
>>>
>>> Mark
>>>
>>>
>>>
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>
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