[vtkusers] Large Image, white rectangle

[David Gobbi]

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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