maandag 8 februari 2016

Processing scans into 3D models (take 1), Kotryna Valečkaitė

Comparison of image processing software 1

Directly after receiving the scans on Tuesday we jumped into processing them into 3D models. To keep it clear we used “Hagrid”(obj. 5) as an example for all of the programs.
As noted in the previous post, this process has multiple steps and in order to gain the highest level of detail, a lot of tweaking is necessary.
The usual procedure goes as follows:
(0. Changing the .ima or .dcm files into program compatible format. Most of our scans were made in .dcm format which was not compatible with multiple programs: so far we tried RenameMaster, which did not work)
  1. Loading the .dcm or .ima files into a 3D processing program. These file formats actually contain only 2D information: the sections of the object. In other words, the 3D model is an interpretation of multiple sections and therefore steps between them might be visible, if the resolution is not high enough.
  2. Selecting threshold and filtering the right information. Depending on the program this step might be automatized. If not, it might be very heavy on your computer. Therefore, a device with a good graphics card and 16GB RAM is advised (it would work on 6 or 8GB RAM, but it goes slow and tends to crash often).
  3. Loading the 3D file into a volume renderer to get an editable mesh (.stl). 
To begin with, we started with Seg3D. This program did not want to read .dcm files, thus we only worked with test files, which were in .ima format. The interface was clear, but to extract minuscule details it needed a lot of filtering and playing with histograms. That was extremely hard on our computers (6-8GB RAM, 2.0-2.03GHz) and took over an hour to get a decent file. Moreover, the final result is given in .nrrd format which later has to be translated to .stl with the help of ImageVis3D. The file looked rather detailed in Seg3D, but the final .stl was worthless.Capture
Hagrid_Seg3D to ImageVis3D_128x128x54mesh_detail
Later on, we received a tutorial from an past student of our supervisor Maaike. It suggested using DeVide. Unlike the previous program this one works on the basis of visual programming. Thus all of the steps can be easily retraced. This program can directly export to .stl reducing the possibility of getting a very rigid mesh, like with Seg3D. Unfortunately, the program did not want to work on our computers.
After this failure we contacted one of the researchers in the faculty of Industrial Design Engineering. He adviced to try out the following programs:
  1. 3D slicer (open source)
  2. Avizo (paid, evaluation copy available after contacting the firm)
  3. Mimics (paid, evaluation copy available after contacting the firm)
The first of the list (3Dslicer) proved to be very user friendly (although it did not read the .dcm files). The information is collected automatically after choosing a preset and is quite precise. One can also select if to smooth the surface: both outputs are interesting in form, with the edgy one as an expressive interpretation of a kitschy object of the past. If used for the final product, more mesh post-processing is necessary
3DSlicer_screenshot
Hagrid_3DSlicer_nonsmoothedges_detail (1)
Hagrid_3DSlicer_smoothedges_detail
To be continued…

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