[Insight-developers] Image-based cost function

[Dan Mueller]

Hi,

I am developing a simple cost function which computes the value and 
derivative by interpolating a single underlying image (I have been 
unable to find an existing class which achieves this). For the 
GetValue() method, I have followed the ImageToImageMetric and defined an 
InterpolatorType and Get/SetInterpolator methods (allowing the user to 
define the interpolation method at run-time).

I wish to do something similar for the GetDerivative() method, but the 
gradient image functions (eg. CentralDifferenceImageFunction and 
GaussianDerivativeImageFunction) do not share a common base class 
(except for ImageFunction which lacks the overriden output type). The 
output types for these two functions are different (Vector for 
GaussianDerivativeImageFunction and CovariantVector for 
CentralDifferenceImageFunction).

*My first question:* Why are the output types different for these two 
functions? I would have thought they compute similar information and 
would therefore have the same output type.

I assume (I have not tried this yet so I could be wrong) that if these 
two functions had the /same/ output type (ie. both Vector or both 
CovariantVector) then I could define a GradientImageFunctionType in my 
cost function similar to below:

typedef Vector< CoordRepType, ImageDimension > GradientOutputType;
typedef ImageFunction< GradientOutputType, CoordRepType > 
GradientImageFunctionType;
itkSetObjectMacro( GradientImageFunction, GradientImageFunctionType );
itkGetConstObjectMacro( GradientImageFunction, GradientImageFunctionType );

The user would then be able to specify the gradient image function at 
run-time (which offers more control than using an explicitly typed 
function). At present, the only way of achieving this is to template the 
cost function over the GradientImageFunctionType, which is not very nice 
for wrapping.

*My second question:* If there is no good reason for these functions to 
have different output types, is it possible to change the output types 
to be the same? Do I submit a bug to request this? Furthermore, is there 
some merit in creating a base GradientImageFunction class from which 
these (and any other) image functions derive?

Thanks for your help.

Cheers, Dan
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.itk.org/mailman/private/insight-developers/attachments/20070709/2e1c3296/attachment.html