[vtkusers] what does the "SetLevel" (I mean the level value) do in vtk?
omahdi at gmx.de
Fri Jun 23 18:34:53 EDT 2006
"level" and "window" (or "window level" and "window width") are
parameters used to describe a certain mapping of (arbitrary) real values
onto a given closed interval. For values l and w (for level and
window), the interval [l-(w/2); l+(w/2)] is linearly mapped onto the
full "target interval" (say, [t0; t1]). Any values in the domain that
are less than l-(w/2) or greater than l+(w/2) are mapped to t0 and t1,
kdsfinger at gmail.com wrote:
> The SetWindow and SetLeve often come together (or SetWindowLevel). I
> understand the window gives a range of the color that vtk is going to
> deal with and cast those out of range to the two ends. Level value is
> usually set in the middle of that range. But I don't understand what
> does the level value stands for.
When dealing with colors, the target interval often corresponds to the
color intensity range your display can handle, and the level/window
parameters are used to describe how scalar values should be mapped to
that range. There is a close relation between level/window and
brightness/contrast, although they are not exactly the same:
> If I adjust the level value lower then the image looks brighter.
By lowering the level value and leaving the window width unchanged,
smaller scalars are effectively mapped to higher values, making the
image brighter. "Brightness" and "contrast" can be seen as a more
intuitive way to describe the same kind of mapping for adjusting the
overall optical appearance of an image (in the special case where source
and target intervals are the same).
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