[Insight-users] NumericLimits::min float / int Inconsistency Workaround?

[Geoff Topping]

Hi all,

I'm trying to make an itk::BinaryThresholdImageFilter with a lower bound that includes all values larger than zero.  Doing this in a generic way has proven difficult due to the inconsistency in how itk::NumericLimits reports min values for float or integer types.

To clarify, this code:

    std::cout << "NumericTraits float min: " << itk::NumericTraits::min() << std::endl;
    std::cout << "NumericTraits signed short min: " << itk::NumericTraits::min() << std::endl;

outputs this:

NumericTraits float min: 1.17549e-38
NumericTraits signed short min: -32768

And since I'm working with signed short pixels, I can't use NumericTraits::min() to set the lower threshold for my filter (although I presumably could if I was using float pixel type).


This issue is not unique to itk::NumericTraits, but is present in std::numeric_limits as well, for reasons that are irrelivant to this discussion.


My question: Is there a reccommended ITK style workaround for this?

I want to be able to set the lower-threshold for my filter in a generic way, so don't want to set it to constants 1 (integer), as that would be well above the minimum positive value for a float type pixel.

I can't use NumericTraits to get the positive minimum value representable by the type, although NumericTraits seems to be the standard way of getting this sort of information in ITK code.

I could use a separate thresholding step to get a mask image with NumericLimits::Zero for values between NumericLimits::NonpositiveMin and NumericLimits::Zero and NumericLimits::One outside that range, and then multiply my original image by this mask to get a nonnegative image, and then apply a separate threshold filter on that, but I shouldn't need to do those extra steps.


Notably, there exist implmentations of similar functions to resolve this, including one in the Boost libraries:

http://www.boost.org/doc/libs/1_38_0/libs/numeric/conversion/doc/html/boost_numericconversion/bounds___traits_class.html

I'm not using any Boost code in my current programs, though.


Is there a reason NumericTraits doesn't have a function to provide the value I need?

NumericTraits does have a NonpositiveMin() function, for a similar purpose, which is implemented differently for float and integer types:

static float NonpositiveMin() { return -vcl_numeric_limits::max(); }

static int NonpositiveMin() { return vcl_numeric_limits::min(); }


Thanks,
Geoff Topping


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