[vtkusers] Smooth label-map volume rendering

Sat Jun 9 15:16:25 EDT 2018

Thank you for the information.

Do these rendering options allow smoothing (low-pass filtering that reconstructs the continuous signal from discrete samples)?

Is visualization of overlapping segments supported? I know that generating new label value for each intersection combination and setting appropriate color and opacity value could be a solution. However, this is only practical if number of segments is small (up to 16 segments a label value could be a bitfield which encodes presence of each segment), but not a generally applicable solution, we need support visualization up to about 200 potentially overlapping segments. It is also a difficulty that current image processing filter implementations cannot operate directly on bitfield data (that was the main motivation for us to use to choose per-segment volumes instead of bitfield volumes for overlapping segment storage).

Andras

From: Sankhesh Jhaveri <sankhesh.jhaveri at kitware.com>
Sent: Friday, June 8, 2018 3:06 PM
To: Andras Lasso <lasso at queensu.ca>
Cc: Bertram Sabrowsky-Hirsch <Bertram.Sabrowsky-Hirsch at risc-software.at>; vtkusers at vtk.org
Subject: Re: [vtkusers] Smooth label-map volume rendering

Hi Andras,

Note that the vtkGPUVolumeRayCastMapper already supports labeled data rendering.

Take a look at TestGPURayCastCompositeMask and TestGPURayCastCompositeMaskBlend.

Sankhesh

On Thu, Jun 7, 2018 at 12:08 PM Andras Lasso <lasso at queensu.ca<mailto:lasso at queensu.ca>> wrote:
I would be interested in a good solution to this, too.

In 3d Slicer, we’ve been using flying edges filter, which creates usable (non-blocky) surfaces very quickly (suitable for interactive editing). The limitation is that we still need a smoothing filter to avoid all staircase artifacts, and that it increases update time by about a magnitude.

We’ve been evaluating using multi-volume rendering for displaying segmentation in 3D, to achieve faster updates and nicer transparent renderings. Multi-volume rendering is good because we can apply Gaussian smoothing on each input volume to get correctly reconstructed (non-blocky) surface and we can display overlapping segments. However, this Gaussian smoothing takes some time (still competitive with surface smoothing) and multi-volume renderer does not support shading yet (this is the blocking issue right now).

Andras

From: vtkusers <vtkusers-bounces at public.kitware.com<mailto:vtkusers-bounces at public.kitware.com>> On Behalf Of Bertram Sabrowsky-Hirsch
Sent: Thursday, June 7, 2018 3:54 AM
To: vtkusers at vtk.org<mailto:vtkusers at vtk.org>
Subject: [vtkusers] Smooth label-map volume rendering

Hi all,

I am working with volume data before and after a classification algorithm.
The input volume has ushort intensity values, the output volume is a label-map where the values indicate each voxels class/label (background=0, vessel=1, aneurysm=2, …).

I am visualizing the input volume with a opacity transfer function that simulates a threshold filter (e.g. control points: 799=0.0, 800=1.0) and the result is a nice and smooth visualization of the volume.

However, the output volume has this blocky Minecraft style effect. The opacity transfer function has the control points: 0=0.0, 1=1.0 and I use the color transfer function to distinguish the classes/labels.
Is there a way to visualize the output volume in a similar way as the input volume? I considered generating iso-surface meshes and smooth those, but this is not really an option. I also don’t really understand why this is an issue because the
Input volume is also rendered with a distance of 1 between the two opacity thresholds. Are the volumes handled differently by vtk and how?

Input volume:
[cid:image001.jpg at 01D3FE56.AEDC44B0]

Output volume:
[cid:image002.jpg at 01D3FE56.AEDC44B0]

Kind regards,
Bertram
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Sankhesh Jhaveri
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