[vtkusers] help for rendering a large amount of images

[David Gobbi]

Hi Henry,

Please reply to the vtk list, not just to me.

You're requirement of rendering "thousands of medical images" is
way too vague.  Do you need to render them all simultaneously,
i.e. will they all be on screen at the same time?  I really do not
understand what you are trying to do.

The vtkImageDataStreamer will be no help to you, because it always
loads the entire volume.  It's job is to pull the data through the pipeline
in small chunks, but the end result is still that the whole volume ends
up in memory.

Yes, vtkImageReslice can show a sagittal or coronal view by only
streaming a small part of the volume into memory, but this will only
work with certain reader classes.  For example, the vtkTIFFReader
always reads entire slices, so it cannot read just one row of a
slice that vtkImageReslice can then incorporate into a sagittal view.
In fact, I think that only vtkImageReader2 can stream individual
rows or columns of an image from disk.  The other readers can
only stream the data slice-by-slice.

You should seriously consider my recommendation of using memory
mapping.  If you simply map a flat file to a memory address and then
use that memory address as a pixel data inside a vtkImageData, then
the operating system can make all the decisions about how and when
to load the data from disk.

 - David


On Tue, Nov 3, 2015 at 10:33 AM, Henry Blanco <henry.blanco at cbiomed.cu>
wrote:

> Thanks David for your soon reply. Ok, my problem is to load and render
> thousands of medical images,
> organized into series, by using VTK, but considering strong limitations
> in terms of RAM (e.g., only 128 or 256 MB of RAM available).
>
> To achieve this task, we have tried to use the "vtkImageDataStreamer"
> class, but we have failed. This class seems to load the whole volume into
> memory, therefore loading 2000 CT images (1GB) into memory may fail if
> we consider just 128 MB of RAM.
>
> We are thinking to partition the whole volume into K blocks and to load
> a block of images into memory just when it's needed. The illusion of
> having the whole volume loaded in memory could be achieved by
> uploading/downloading one or more blocks of images to/from memory when
> needed. I'm wondering whether exist some vtk classes which can be used
> to picture a different view than the original (e.g., sagittal, coronal,
> or even oblique) without loading the whole volume of images.
>
> Henry
>
> On lun, 2015-11-02 at 17:29 -0700, David Gobbi wrote:
> > What kind of views will you need?  Do you just have to view the
> > original
> > slices?  If so, then the VTK pipeline's streaming will make the job
> > easy.
> > If you need orthogonal or oblique views, things are more difficult.
> > Also,
> > how is the data stored on disk?  If the whole volume is stored on disk
> > as a single flat file, then you can memory map the file.
> >
> >
> >  - David
> >
> > On Mon, Nov 2, 2015 at 4:10 PM, Henry Blanco <henry.blanco at cbiomed.cu>
> > wrote:
> >         Hello guys, I need some hints on how to render a large amount
> >         of images
> >         (e.g., thousands of images) using just few RAM resources
> >         (e.g., 128 MB)
> >         using the vtkImageReslice class for the whole volume.
> >
> >         Thanks in advance
> >
> >         Henry
>
>
>
>
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