[vtkusers] window/level concept

[Edward Bachta]

That's odd, because in the VTK User's Guide v4.0 on page 127 the
window/level scheme is described differently. There is a diagram:
           
             ____________
            /
           /
__________/
         | ^ |
           L           
         <-W->

This is my understanding:

Level (L) designates the center of the range of values mapped to
grayscale. Window designates the extent of the range to either side of the
level. Thus, the range mapped is (level-window/2) to (level+window/2). For
a positive window value, regions less than (level-window/2) are clamped to
black and regions greater than (level+window/2) are clamped to white.  
Regions at (level) are 50% gray. With a negative window value you get the
inverse image.

Based on what I have observed in my implementations using vtkImageViewer,
this is correct. (VTK CVS version circa Sept 24th)

-- 
Ed Bachta
ebachta at ncsa.uiuc.edu

On Wed, 16 Oct 2002 anast.jm at pg.com wrote:

> 
> Steffen,
> 
> If you think of the image histogram, the window is the range of values that will
> be mapped to your display, the level is where in the histogram this range
> begins. For example if you have a 4096 bin histogram, a window of 250 and a
> level of 1000, this would map bins 1000-1250 full scale onto your display, all
> other values would be clipped. The Window/Level concept is also know in
> photographic circles as contrast/bightness and for cameras gain/offset....john
> 
> 
> 
> 
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> 
> From: Steffen Oeltze <Steffen.Oeltze at Student.Uni-Magdeburg.DE>
> @public.kitware.com on 10/16/2002 10:00 AM ZE2
>                                                                                                                    
>      Steffen Oeltze <Steffen.Oeltze at Student.Uni-Magdeburg.DE>           To:   VTK users                            
>                                           @public.kitware.com        <vtkusers at public.kitware.com>                 
>                                                                         Cc:    (bcc: John Anast-JM/PGI)            
>                                                                 Subject:      [vtkusers] window/level concept      
>                   Sent by:  vtkusers-admin at public.kitware.com                                                      
>                                           10/16/2002 04:00 AM                                                      
>                                                                                                                    
>                                                                                                                    
> 
> 
> 
> 
> Dear VTK-users,
> 
> I'm not familiar with the window/level concept of the vtkImageMapper. Could
> anybody give me some insight please ?
> 
> Thanks,
> Steffen
> 
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