[vtkusers] Why does VTK use doubles for color?

[David Thompson]

> Is there a reason that unsigned chars are not used for all things  
> related to color? For example
> vtkProperty::SetColor(double,double,double) //expects values from  
> 0.0 to 1.0
> http://www.vtk.org/doc/nightly/html/classvtkProperty.html#aa591fc54d4e2d21e2c7a97ef7cd2a993
> vtkViewPort::SetBackground(double,double,double) //expects values  
> from 0.0 to 1.0
> http://www.vtk.org/doc/nightly/html/classvtkViewport.html#a85eaf3ee2b0e49423efbaa41de17112d
> Wouldn't it be more natural to define these as
> vtkProperty::SetColor(unsigned char,unsigned char,unsigned char) // 
> expects values from 0 to 255
> vtkViewPort::SetBackground(unsigned char,unsigned char,unsigned  
> char) //expects values from 0 to 255
> ?

Hi David,

Using double instead of unsigned char allows for display devices that  
have more than 24-bit color depth and makes image processing (such as  
tone mapping, sharpening, blurring, etc.) less susceptible to the  
accumulation of trunctation errors when many steps are involved.

	David