[vtkusers] vtkImageActor and scaling

[endlosschleife1]

It's possible that I'm misinterpreting the performance results of my
implementation and that applying the window level lookup table is actually
not what makes the difference. I'm comparing a vtkActor2D/vtkImageMapper
based and a vtkImageActor based implementation of something that shows a
series of images one by one with a specific window/level.

If the window/level is not the issue, how much of a difference in
performance drop for the vtkImageActor implementation would be expected?

I have 700 images (512 x 512, 12 bits stored), rendered into a 512 x 512
viewport). vtkActor2D/vtkImageMapper takes about 8 seconds, vtkImageActor
about 26 seconds to render the whole series. If I additionally resample my
data to add a scale to best fit to the vtkActor2D/vtkImageMapper
implementation I get to 18 seconds (that was my starting point to look for
accelarated scaling). There is no visible difference when I add scaling to
the vtkImageActor. That means that I'm getting much faster scaling for the
vtkImageActor based implementation, but that overall it still performs
slower. Unless there is some other bottleneck in my implementation.

Mark



2010/11/30 David Gobbi <david.gobbi at gmail.com>

> On Tue, Nov 30, 2010 at 7:10 AM, endlosschleife1 <
> endlosschleife1 at googlemail.com> wrote:
>
>  I was actually looking for accelerated scaling, so this sounds like
>> vtkActor2D is not be the right thing for that.
>>
>
> For accelerated scaling, you need to use vtkImageActor.
>
> I'm not sure, but it looks like my implementation probably doesn't use any
>> GPU acceleration (it seems to be pure image data filtering). It still seemed
>> to be not as performant as I expected (compared to an implementation where I
>> only used VTK for the imaging pipeline, but did the LUT application
>> and visualization separetely).
>>
>
> The vtkImageMapper doesn't have accelerated window/level either.  It does
> all the computations on the CPU and then uses glDrawPixels() to render the
> image.
>
>
>>  I create a vtkWindowLevelTable, set the window and center, and then call
>> build on the lut. Then I used it with a vtkImageMapToColors instance:
>>
>> vtkImageMapToColors *color = vtkImageMapToColors::New();
>> color->SetLookupTable(lut); // lut is the vtkWindowLevelTable
>> color->SetInput(...) // some vtkImageData
>>
>
> Yes, that looks typical.  Make sure that you call table->SetRampToLinear()
> because by default, a VTK lookup table uses a curved ramp instead of a
> linear ramp (I was shocked when I discovered this for the first time).
>
>   David
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.vtk.org/pipermail/vtkusers/attachments/20101130/2794add9/attachment.htm>