old_contents: def is_cellomics_image(fn):
      """Determine whether a file is a Cellomics image.
  
      Parameters
      ----------
      fn : string
          The filename of the file in question.
  
      Returns
      -------
      is_cellom : bool
          True if the filename points to a Cellomics image.
      """
      is_cellom = fn.endswith('.C01') or fn.endswith('.c01')
      return is_cellom
  
  
  def is_cellomics_mask(fn):
      """Determine whether a file is a Cellomics mask image.
  
      Parameters
      ----------
      fn : string
          The filename.
  
      Returns
      -------
      is_mask : bool
          True if the filename points to a Cellomics mask image.
      """
      is_mask = fn.endswith('o1.C01') or fn.endswith('o1.c01')
      return is_mask
  
  
  
new_contents: import os
  
  
  def fn_has_ext(fn, ext, case_sensitive=False):
      """
      Determine whether a file has a particular extension.
  
      Parameters
      ----------
      fn : string
          The filename of the query file.
      ext : string
          The extension being checked.
      case_sensitive : bool
          Whether or not to treat the extension as case sensitive.
  
      Returns
      -------
      file_has_ext : bool
          True if the filename has the specified extension.
      """
      fn_ext = os.path.splitext(fn)[1][1:]
      if case_sensitive:
          file_has_ext = fn_ext == ext
      else:
          file_has_ext = fn_ext.lower() == ext.lower()
      return file_has_ext
  
  
  def is_cellomics_image(fn):
      """Determine whether a file is a Cellomics image.
  
      Parameters
      ----------
      fn : string
          The filename of the file in question.
  
      Returns
      -------
      is_cellom : bool
          True if the filename points to a Cellomics image.
      """
      is_cellom = fn_has_ext(fn, 'C01') or fn_has_ext(fn, 'DIB')
      return is_cellom
  
  
  def is_cellomics_mask(fn):
      """Determine whether a file is a Cellomics mask image.
  
      Parameters
      ----------
      fn : string
          The filename.
  
      Returns
      -------
      is_mask : bool
          True if the filename points to a Cellomics mask image.
      """
      is_mask = fn.endswith('o1.C01') or fn.endswith('o1.c01')
      return is_mask
  
  
  
subject: Add DIB files to cellomics file filter