Make copy function virtual so subclasses can implement there own so that they are copied correctly when used polymorphically.
Implement copy function for subpicture subclasses that need it.
Subclasses of subpicture are properly copied so this is no longer needed.
Use std::abs for doing absolute value.  Simplification of filtering and using C++11 constexpr to reduce computation.
Use C++11 style >> for templates.
Use C++11 style >> for templates.