[vtk-developers] [EXTERNAL] Software vs hardware interpolation

Fri Mar 23 10:52:24 EDT 2012

Hi Thomas,

What happens when you set vtkVolumeProperty::SetInterpolationType to
nearest neighbor ?

j.

On Thu, Mar 22, 2012 at 1:38 PM, Kilgus, Thomas <t.kilgus at dkfz-heidelberg.de
> wrote:

> Thank you guys very much for the feedback!
>
> @David: As you guessed, we use a vtkPolyDataMapper (including vtkActor and
> a vtkTexture) inside our application to render the slices in 2D and 3D (due
> to historical reasons). In fact, I tried to employ your new image mappers
> last year, but run into some issues with our own interaction and further
> requirements related to our own applications. Hopefully, we will have
> resources to investigate more in adapting our parts for your mappers in the
> future. I would really like to use them, but unfortunately right now it's
> not possible for us.
>
> @Kenneth: Adding another validation image could be an interesting option.
> Where exactly can I find the mentioned examples?
>
> Regards
> Thomas
>
>
> -----Ursprüngliche Nachricht-----
> Von: David Gobbi [mailto:david.gobbi at gmail.com]
> Gesendet: Mittwoch, 21. März 2012 16:22
> An: Kilgus, Thomas
> Cc: vtk-developers at vtk.org
> Betreff: Re: [vtk-developers] [EXTERNAL] Software vs hardware interpolation
>
> Hi Thomas,
>
> What mapper are you using?  The vtkImageMapper?  A vtkActor with a
> vtkTexture?  Or a vtkImageActor?  All three use different OpenGL
> paths.
>
> From your images, I'm going to guess, like Kenneth, that you are using
> a vtkTexture.  If OpenGL only supports power-of-two textures, the
> vtkTexture code will resample its input to the nearest power of two,
> i.e. a 5x5 texture is resampled (in software) to 8x8.  If OpenGL
> supports non-power-of-two textures, the 5x5 texture is displayed
> directly.
>
> Back when I used vtkTexture to display images (eight years ago or so),
> I always padded my images up to a power of two and remapped the
> texture coordinates, specifically to avoid this unwanted resampling
> step in vtkTexture.  Afterwards, I switched to vtkImageActor which
> handles non-power-of-two images just fine.  Recently, I wrote a whole
> new set of image mappers which are included in VTK 5.10.
>
>  - David
>
>
> On Wed, Mar 21, 2012 at 8:21 AM, Moreland, Kenneth <kmorel at sandia.gov>
> wrote:
> > I don't claim to be an expert here, but the interpolation method (nearest
> > vs. linear) is controlled via an OpenGL flag to glTexParameter.  If VTK
> is
> > not properly setting this flag, this could be a bug, but a look at
> > vtkOpenGLTexture looks as if the flag should be set correctly.
> >
> > Traditionally (circa 15 years ago) the nearest lookup was considered
> faster
> > and the linear lookup was considered more accurate.  Nowadays, graphics
> > cards have special interpolating hardware in their texture units that
> allows
> > them to do the linear interpolation with no extra time cost.  It could be
> > that the driver for this particular hardware is doing the linear
> > interpolation anyway since there is no added time cost.
> >
> > VTK has been dealing with rendering difference between software and
> hardware
> > rendering as well as differences between different hardware architectures
> > for, like, ever.  Thus, the VTK testing framework accepts multiple valid
> > images for any test.  You just add image files with the same name but
> with
> > _1, _2, etc. added to the filename.  (There are lots of examples in the
> > existing baselines.)
> >
> > So, the easy solution is just to check in a new image into the baseline
> > image repository.  The real question is, how much do you really care that
> > you are getting linear instead of nearest interpolation?  Do you have a
> use
> > case other than this pathological test?
> >
> > -Ken
> >
> > From: "Kilgus, Thomas" <t.kilgus at Dkfz-Heidelberg.de>
> > Date: Wed, 21 Mar 2012 14:24:39 +0100
> > To: "vtk-developers at vtk.org" <vtk-developers at vtk.org>
> > Subject: [EXTERNAL] [vtk-developers] Software vs hardware interpolation
> >
> > Hi,
> >
> >
> >
> > as mentioned in my previous post
> > (http://vtk.1045678.n5.nabble.com/software-rendering-td5557078.html ), I
> > observed different interpolation behaviors in software and hardware
> > rendering of images in VTK.
> >
> >
> >
> > Here you can see an example:
> > http://cdash.mitk.org/testDetails.php?test=2749290&build=107877
> >
> >
> >
> > The test shows the result of an image rendered with software rendering.
> The
> > input 5x5 pixel image is scaled (interpolated) to 8x8. If you render the
> > same image with hardware support, a nearest neighbor interpolation will
> be
> > applied and the result will look like the ValidImage on the bottom of the
> > page. I don't think that any interpolation can be considered wrong or
> right,
> > but I think both, software and hardware rendering, should have a common
> > default behavior.
> >
> >
> >
> > Please can anyone comment on this? Is there any possibility to enforce
> the
> > same interpolation in software rendering? For reliable testing in
> different
> > environments it is necessary both rendering methods act with the same
> > default behavior, since it is not deterministic whether your machine is
> able
> > to render with hardware support or with software rendering. (For
> instance a
> > VPN connection established to a windows machine blocks the GPU for some
> > reason, Virtual Machines show different behavior etc.)
> >
> >
> >
> > Regards
> >
> > Thomas
> >
> >
> >
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