[vtkusers] Convert from RGBA values to the index in the VTK Lookup Table

[Frederic Perez]

Hi Kanghong Li,

 --- Kanghong Li <kli at issi-hsv.com> escribió: 
> Anyone knows a way to convert from RGB values (3 numbers + A if
> needed) to the scalar/index (a value between 0 and 1) in the default
> vtk lookup table? Thanks.
> 
> For example, RGB (51,51,255), can I get a value between 0 and 1
> (index to the vtk lookup table) from that 3 numbers?

A possibility is to use the luminance.
A common expression is given by
 0.299*R + 0.587*G + 0.114*B
or 
 A*(0.299*R + 0.587*G + 0.114*B).

Notice that if your values range between 0 and 255 you will have
to divide them by 255 (the R, G, B values of the previous ex-
pressions should lie in [0..1]).

HTH,

Frederic Perez



		
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