          """ Validates that the given filter/nfilter files exist, are image files and are unique
  
          Parameters
          ----------
          filter_files: str, list or ``None``
              The list of filter file(s) passed in as command line arguments
          nfilter_files: str, list or ``None``
              The list of nfilter file(s) passed in as command line arguments
  
          Returns
 
</s> remove         nfilter_files: str, list or ``None``
 </s> add         nfilter_files: list or ``None`` </s> remove     filter_files: str, list or ``None``
 </s> add     filter_files: list or ``None`` </s> remove     nfilter_files: str, list or ``None``
 </s> add     nfilter_files: list or ``None`` </s> remove                          filter_files: Optional[Union[str, List[str]]],
                         nfilter_files: Optional[Union[str, List[str]]]) -> Tuple[List[str],
                                                                                  List[str]]:
 </s> add                          filter_files: Optional[List[str]],
                         nfilter_files: Optional[List[str]]) -> Tuple[List[str], List[str]]: </s> remove             filt_files = [files] if isinstance(files, str) else files
            filt_files = [] if filt_files is None else filt_files
 </s> add             if isinstance(files, list) and len(files) == 1 and os.path.isdir(files[0]):
                # Get images from folder, if folder passed in
                dirname = files[0]
                files = [os.path.join(dirname, fname)
                         for fname in os.listdir(dirname)
                         if os.path.splitext(fname)[-1].lower() in _image_extensions]
                logger.debug("Collected files from folder '%s': %s", dirname,
                             [os.path.basename(f) for f in files])

            filt_files = [] if files is None else files
        filter_files: list or ``None``
          """ Validates that the given filter/nfilter files exist, are image files and are unique
  
          Parameters
          ----------
        filter_files: list or ``None``
              The list of filter file(s) passed in as command line arguments
          nfilter_files: str, list or ``None``
              The list of nfilter file(s) passed in as command line arguments
  
          Returns
keep keep keep keep replace keep keep keep keep keep
 Face-filter updates:
  - Allow selecting folder as well as multiple images
  - Lower default threshold and update helptext
  - bugfix: detector error when using all aligned faces
  - Standardize output folder name 
scripts/extract.py