Is there any code or example to perform histogram equilization in itk or simple itk?
Unfortunately, ITK does not have the classical histogram equalization (the example pointed to by @dzenanz is a variant but does not provide settings equivalent to the classical filter). As a consequence SimpleITK does not have the classical histogram equalization.
Having said that, you can easily roll your own in Python as shown in this SimpleITK Jupyter notebook. The function name there is not surprisingly
New in the ITK v5.1 development branch is the
SetReferenceHistorgram method. When provided an equal level reference histogram, this will perform the classical histogram equalization algorithm.