[vtkusers] color level ... what does it do? Newbie question alert :)

Amy Squillacote amy.squillacote at kitware.com
Mon Aug 21 09:25:43 EDT 2006

Hi Anja,

SetColorWindow does set the range, but it doesn't necessarily go from 0 
to the ColorWindow value; where the range starts and ends depends on the 
value of ColorLevel. Use SetColorLevel to specify the center of the 

For example, if you set ColorWindow to 200 and ColorLevel to 100, then 
the range goes from 0 to 200 as you describe in your second paragraph. 
However, if you set the ColorLevel to 150, then the range goes from 50 
to 250, and the outliers are mapped to 50 and 250, depending on whether 
they are above or below the range.

- Amy

Anja Ende wrote:
> Hi all,
> Was looking at SetColorWindow and SetColorLevel functions in the 
> various vtk image viewers. I just have a confusion about what 
> SetColorLevel does.
> I think SetColorWindow basically maps the input pixel values to some 
> output pixel value range. S, if we have an input of say...0, 60,000 
> and we set the color window to 0, 200, for example...than the input 
> pixel values are linearly mapped to this range and the outliers are 
> mapped to 0 and 200 depending on which side they lie... Am I correct?
> Now, I have no idea what SetColorLevel does? I know that it seems to 
> be related soemhow to the brightness of the image and I guess it is 
> scaling the lower intensity pixels... However, can someone explain 
> what exactly it is doing to the pixel values...
> For example, if I map the input values of 0-60000 to 0-200 and set the 
> color level to 100, what exacxtly will it do to the pixel values...
> Sorry for asking such a newbie question...
> Thanks,
> Anja
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