[vtkusers] invert the color of pixels

[Shang Mu]

Thanks for the suggestion, Cory.

But I really don't like that approach. Instead of just a single operation of 
getting the complement of an number, I have to use float point 
multiplication....

Is there a canonical way to access the raw image data in vtk? I'd really 
like to know that if there is one.

Shang


----- Original Message ----- 
From: "Cory Quammen" <cquammen at cs.unc.edu>
To: "Shang Mu" <smu.email at gmail.com>
Cc: <vtkusers at vtk.org>
Sent: Monday, August 27, 2007 7:07 PM
Subject: Re: [vtkusers] invert the color of pixels


> Shang,
>
> Try a vtkImageShiftScale object to apply the transformation
>
> 255 - px = (px - 255.0) * -1.0
>
> to each pixel where px is the initial pixel value. It will probably go
> something like:
>
> vtkImageShiftScale inverter = vtkImageShiftScale::New();
> inverter->SetInput(myImage);
> inverter->SetOutputScalarTypeToUnsignedChar();
> inverter->SetShift(-255.0);
> inverter->SetScale(-1.0);
> ...
>
> This will subtract 255 from all your values and then "mirror" them
> around 0. You may want to set the shift value to something like -255.1
> just to make sure the "mirrored" numbers will clamp down to the
> appropriate unsigned char.
>
> Cory
>
> On 8/27/07, Shang Mu <smu.email at gmail.com> wrote:
>> I'm trying to invert the color of an image of type unsigned char, i.e.
>> black to white and white to black. To my suprise i could not find a
>> vtk filter that does this job. Does vtk have such a filter somewhere?
>>
>> I've went through the vtk filters several times and could not find
>> such a filter. The "invert" in vtkImageMathematics returns the
>> reciprocal of each pixel, not in the sense of image color.
>>
>> Thanks!
>>
>> Shang
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>
>
> -- 
> Cory Quammen
> Department of Computer Science
> University of North Carolina at Chapel Hill
> http://www.cs.unc.edu/~cquammen