[vtkusers] Large Image, white rectangle

[Joe Miller]

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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