          """
          error = False
          retval: List[List[str]] = []
          for files in (filter_files, nfilter_files):
              filt_files = [files] if isinstance(files, str) else files
              filt_files = [] if filt_files is None else filt_files
              for file in filt_files:
                  if (not os.path.isfile(file) or
                          os.path.splitext(file)[-1].lower() not in _image_extensions):
                      logger.warning("Filter file '%s' does not exist or is not an image file", file)
                      error = True
 
</s> remove         filter_files: str, list or ``None``
 </s> add         filter_files: list or ``None`` </s> remove             logger.info("'%s' not a png. Returning empty array", filename)
 </s> add             logger.debug("'%s' not a png. Returning empty array", filename) </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             raise ValueError("nargs must be provided for FilesFullPaths: {}".format(opt))
 </s> add             raise ValueError(f"nargs must be provided for FilesFullPaths: {opt}") </s> remove             raise ValueError("nargs not allowed for Slider: {}".format(opt))
 </s> add             raise ValueError(f"nargs not allowed for Slider: {opt}")
            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
          """
          error = False
          retval: List[List[str]] = []
          for files in (filter_files, nfilter_files):
            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
            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
              for file in filt_files:
                  if (not os.path.isfile(file) or
                          os.path.splitext(file)[-1].lower() not in _image_extensions):
                      logger.warning("Filter file '%s' does not exist or is not an image file", file)
                      error = True
keep keep keep keep replace 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