[Insight-users] [ITK Community] ScalarToRGBColormapImageFilter custom range

[Brian Helba]

Hi Wei,

You didn't specify a version of ITK that you were using, so I will assume
the most recent release (v4.4.2) for my comments.

First, note that itk::ScalarToRGBColormapImageFilter will always get the
maximum pixel value of the input image and re-call
"m_Colormap->SetMaximumInputValue"
with it [1]. This happens intrinsically when running the
ColormapImageFilter, so I believe there is really no place in user code
that you could set a different maximum that wouldn't be overwritten later.

There is a fairly simple solution, however. The method
itk::HotColormapFunction::SetMaximumInputValue is virtual [2]. You could
create your own subclass of itk::HotColormapFunction, then override
"SetMaximumInputValue" to ignore its parameter and insted set
"m_MaximumInputValue" to be 255 (or even some other value, stored in
another new member variable). Then of course just typedef your new subclass
as the ColormapType and use the rest of your code as normal.

[1]
http://itk.org/gitweb?p=ITK.git;a=blob;f=Modules/Filtering/Colormap/include/itkScalarToRGBColormapImageFilter.hxx;h=2e958db61f7f7639951af24d93baac921534819f;hb=3f8d0a7d84ba3bac4950114e0e0e15f69852496d#l101
[2]
http://www.itk.org/Doxygen44/html/classitk_1_1Function_1_1ColormapFunction.html#a6e3e281b374c86acf427baf2983f879a

Hope this helps.

Enjoy,
Brian



On Tue, Nov 12, 2013 at 1:26 AM, Wei Liu <weiliu620 at gmail.com> wrote:

> Dear itk users,
>
> I'm trying to use ScalarToRGBColormapImageFilter to map a scalar to rgb
> color. According to the document, "The range of values present in the input
> image is the range that is mapped to the entire range of colors". However,
> I want to fix the range of the input image.  That is, no matter what
> intensity range of the input image is, I want the range [0, 255] map to the
> full color range. So far I have tried the following approach:
>
>      typedef itk::Function::HotColormapFunction< ImageType2DF::PixelType,
> RGBImageType::PixelType >  ColormapType;
>      ColormapType::Pointer colormap = ColormapType::New();
>     colormap->SetMinimumInputValue(0);
>     colormap->SetMaximumInputValue(255);
>     std::cout << "max input: " << colormap->GetMaximumInputValue() <<
> std::endl;
>     rgbfilter->SetColormap(colormap);
>
> I can see the maximum input value is correctly set. But it seems the
> ScalarToRGBColormapImageFilter still define the input range by reading the
> input image's min/max value. Did I miss something?
>
> I have a related question: it looks itk does not have a filter to overlay
> a continuous value image onto a gray level intensity image. That is the
> reason I mannually convert the scalar image to rgb image, and overlay it
> onto the gray level intensity image. Is there better way of doing it?
>
> I appreciate your input.
>
> Wei
>
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-- 
Brian Helba
Medical Imaging
Kitware, Inc.
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