How to choose an appropriate value for isovalue?

Hi everyone,

I am currently trying to do 3D visualization of dicom images (they are CT data feet images) packed in a 3D matrix by using isovalue. But I do not know how to choose an appropriate isovalue.

Also, since I do not know how to choose the isovalue, I have just been choosing random values for isovalue. When I run the code, an image appears but I also get an error message saying:

"??? Out of memory. Type HELP MEMORY for your options."

Is this error relevant to the isovalue I have chosen?

So the questions are: 1) How can I choose the appropriate isovalue? 2) How can I not be out of memory?

Answer 1

[Sean de Wolski]

1) The isovalue is essentially the contour value or threshold that you wish to impose. To select one, you need to look at your data and see where you want the contour drawn. You can use imtool() on one of the slices and the pixel region tool to look around and manually pick an isovalue

2) For three-d rendering and isosurface calculation, downsampling can help a lot and not affect the results. For example, if you have a 512x512x512 volumetric image and you downsample by a factor of in each dimension:

Vsmall = V(1:2:end,1:2:end,1:2:end);

MATLAB will have 2^3 or 8x less work to do during the isosurface calculation.