v2.0.0

LocalFilters v2.0.0

This is a major release.

Version 2 of LocalFilters better integrates in the Julia ecosystem as fewer
custom types are introduced:

• To represent hyper-rectangular Cartesian sliding windows, former type
  RectangularBox has been replaced by CartesianIndices.

• Kernels with values or neighborhoods with more complex shape than
  hyper-rectangular Cartesian sliding windows are all represented by abstract
  arrays (with boolean entries to define a neighborhood). The former type
  LocalFilters.Kernel is no longer provided. To account for offsets in the
  indexing, it is recommended to use the
  OffsetArrays package. The
  method LocalFilters.centered(B) can be called to yield a kernel or a
  neighborhood whose index ranges are approximately centered. This method is
  not exported to avoid conflicts (for instance, it has a slightly different
  semantic in OffsetArrays).

Version 2 of LocalFilters provides more general, more consistent, and better
optimized methods:

• Most filtering operations take an optional ordering argument ord right
  before the argument, say B, specifying the kernel or the neighborhood. If
  ord is ForwardFilter, B is indexed as in discrete correlations;
  otherwise, if ord is ReverseFilter, B is indexed as in discrete
  convolutions. The default ordering is ForwardFilter as this is the most
  natural for many filters (except discrete convolutions of course) and as it
  yields faster code. For symmetric kernels and neighborhoods, the ordering has
  no incidence on the result. In LocalFilters version 1, indexing as in
  discrete convolutions was the only rule.

• The API of localfilters! have changed a bit, the syntax is
  localfilters!(dst,A,ord=ForwardFilter,B,initial,update,final=identity) with
  dst the destination, A the source, ord the direction of the filter, B
  the kernel or neighborhood of the filter, initial the value of the initial
  state variable, update a method to update the state variable, and final a
  method to yield the result to store in the destination dst given the value
  of the state variable at the end of visiting the neighborhood.

• Constructor LocalFilters.Indices and helper method
  LocalFilters.localindices may be used as an alternative to localfilters!
  to build custom filters.

• In all filters, a simple neighborhood that is a hyper-rectangular Cartesian
  sliding window can be specified in many different ways. Such a neighborhood
  is represented by an instance of CartesianIndices with unit step ranges.
  Method LocalFilters.kernel(Dims{N},args...) can be called to build such a
  N-dimensional neighborhood from argument(s) args....

• Non-exported LocalFilters.ball method is now type stable. Call
  LocalFilters.ball(Dims{N},r) instead of LocalFilters.ball(N,r).

• The strel method uses uniform arrays from package
  StructuredArrays to
  represent structuring elements with the same value for all valid indices.

• In out-of-place filters, the destination array needs not be of the same size
  as the source array. The local filtering operation is applied for all indices
  of the destination, using boundary conditions to extract the corresponding
  value in the source array. Currently only flat boundary conditions are
  implemented but this may change in the future.

Guidelines for porting code from version 1 to version 2

If the high level API was used, there should be almost no changes, except for
non-symmetric kernels or neighborhoods for which ReverseFilter ordering must
be specified to mimic the former behavior.

At a lower level, the following changes should be done:

• Non-exported union LocalFilters.IndexInterval has been replaced by
  LocalFilters.Axis to represent the type of any argument that can be used to
  define a sliding window axis: an integer length or an integer-valued index
  range.

• Non-exported method LocalFilters.ismmbox has been replaced by
  LocalFilters.is_morpho_math_box.

• Non-exported method LocalFilters.cartesian_region has been replaced by the
  more general and better designed exported method kernel.

• Replace Neighborhood{N}(args...) by kernel(Dims{N}, args...) and
  Neighborhood{N} or RectangularBox{N} by LocalFilters.Box{N}.

• Replace LocalFilters.Kernel by OffsetArrays.OffsetArray.

• Update the arguments of localfilters!: initial is no longer a method but
  the initial state value, update has the same semantics, and final just
  yields the result of the local filter given the last state value. By default,
  final is identity.

• Replace LocalFilters.ball(N,r) by LocalFilters.ball(Dims{N},r) which is
  type-stable.