[vtkusers] Large Image, white rectangle

[Joe Miller]

That makes sense. Thanks everyone for the help.

-joe
--- David Gobbi <dgobbi at imaging.robarts.ca> wrote:
> Hi Joe,
> 
> The vtkImageActor uses an OpenGL texture to display
> the image, so
> hardware texture dimension or memory limitations are
> important.
> 
> The easiest thing to try is to feed the data into
> four ImageActors,
> and then set the DisplayExtent of each Actor so that
> each one
> displays a different quadrant of the image.
> 
>  - David
> 
> 
> On Tue, 6 Jan 2004, Joe Miller wrote:
> 
> > Hi James,
> >
> > Thanks for the quick reply. Though I don't think I
> > clearly stated my problem. The problem I'm having
> > isn't with texture maps its with the image actor.
> When
> > I read in an image 2000x2000 (that's an
> approximated
> > value its around there though) pts or greater and
> try
> > to just render the image actor I get a white
> rectangle
> > instead of the 2d image.
> >
> > I had seen another message posted that had
> described a
> > similar problems with texture maps. I was
> wondering if
> > hardware limitations (to which my Sun Ultra 5 has
> > many) were the cause the image actor couldn't
> display.
> > Though the texture map problem may have been a red
> > herring all together.
> >
> > Anyway, splitting the image is something I may be
> > stuck considering. Though if there are any other
> > thoughts, I'm still open to suggestions.
> >
> > Thanks again for your time.
> >
> > -joe
> >
> > --- James Urquhart <j_urquhart at btinternet.com>
> wrote:
> > > On Tuesday 06 January 2004 4:02 pm, Joe Miller
> > > wrote:
> > > > Hi,
> > > >
> > > > I'm new to VTK and trying to read in and
> display
> > > large
> > > > 2D images (2000 x 2000). However, when I try
> and
> > > > render the image all I get is a white
> rectangle. A
> > > > simple program I wrote
> > >
> > > > I noticed in the archive there were a few
> mentions
> > > of
> > > > texture maps having similar problems. They
> > > described a
> > > > hardware issue that the hardware can only
> handle
> > > > texture maps of certain proportions. I was
> > > wondering
> > > > if anyone knew if I was experiencing the same
> > > problem
> > > > and had any suggestsions of a workaround.
> > >
> > > Joe,
> > >
> > > From what i can see on the net, there appears to
> be
> > > a texture size limit for
> > > opengl on some graphics cards.
> > > Usually the limit is in the 2048x2048 +- range.
> > > Also remember that alot of graphics cards only
> like
> > > textures with dimensions
> > > of the power 2. e.g 16x16, 32x32, 256x256,
> 512x512
> > > ...
> > > Another thing to consider is the amount of
> memory on
> > > the video card. Though
> > > these days, cards typically have 64 / 128mb +,
> which
> > > is plenty for your
> > > typical 3d app. (at least i *hope*)
> > >
> > > You could try splitting your image up into
> smaller
> > > segments, and mapping each
> > > segment onto another polygon. You should easily
> be
> > > able to keep the texture
> > > seamless :)
> > >
> > > e.g for a 2048x2048 texture :
> > >   Have 16 quad's, each representing a 512x512
> block
> > > of the image. (4 along the
> > > top, 4 along the bottom, 4*4).
> > >
> > > -James
> > >
> > >
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