Misprint other


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Some issues tackled during our misprint detection project

[edit] Look-up_Tables

Several parts of our algorithm uses look-up tables to find parameters (ink properties), or to fasten the computation (the whole simulation outside ISET is based on a pre-computed look-up table). We ran in a particular problem of having a look-up that does not sample the space at regular values (see the following image for a 2D example).

Non regular look-up table

This is a problem as to have a fast search in this table, the best thing to do is to use a lexicographic order and then to do a dichotomic search for each coordinates, this ends up with the results illustrated in the previous image. This can be overcome by a local approximation of our function at each point of the table, if this approximation is possible. Though this is far from being optimal as some sample have a large influence and others are almost useless.

To avoid this problem we used the following method:

  • Define values in the space that will be the new entries of the table (probably much more values than before).
  • Use your current method (that is supposed to be long) to compute values for the new table, from the old table.
  • Now we can use this new balanced table in a fast search, while still having reliable results.

[edit] VTK Visualization

After images have been converted to the CMYK colorspace (but still in the jpg format) with ImageMagick, you can visualize them with VTK, using the program "map_image_on_vtp" in the vtkbin directory, the usage is:

./vtkbin/map_image_on_vtp CMYKimage.jpg deformation_type debugging

The second argument (debugging) may be 0 or 1, 0 meaning no debugging, 1 meaning that you will be running the debugging mode and the program will print a lot of informations on internal variables. You probably do not want to do that unless you are modifying the code.

The third argument (deformation_type) may have values ranging from 0 to 5

  • 0: no transformation
  • 1: Bowl shape
  • 2: Sphere shape
  • 3: Cylinder shape
  • 4: Some random elevations
  • 5: Folded paper

You can see some example here:

Bowl shape Sphere shape Folded paper
Bowl shape Sphere shape Folded paper

When running the program, after the first window pops up, you can switch between w and s keys to see the grid or the coloured image. You can press q or e to exit the window, it will then show the image projected back in the z=0 plan.

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