text: """Standard test images.
  
  For more images, see
  
   - http://sipi.usc.edu/database/database.php
  
  """
  
  import os as _os
  
  from ..io import imread
  from skimage import data_dir
  
  
  def load(f):
      """Load an image file located in the data directory.
  
      Parameters
      ----------
      f : string
          File name.
  
      Returns
      -------
      img : ndarray
          Image loaded from skimage.data_dir.
      """
      return imread(_os.path.join(data_dir, f))
  
  
  def camera():
      """Gray-level "camera" image.
  
      Often used for segmentation and denoising examples.
  
      """
      return load("camera.png")
  
  
  def lena():
      """Colour "Lena" image.
  
      The standard, yet sometimes controversial Lena test image was
      scanned from the November 1972 edition of Playboy magazine.  From
      an image processing perspective, this image is useful because it
      contains smooth, textured, shaded as well as detail areas.
  
      """
      return load("lena.png")
  
  
  def text():
      """Gray-level "text" image used for corner detection.
  
      Notes
      -----
      This image was downloaded from Wikipedia
      <http://en.wikipedia.org/wiki/File:Corner.png>`__.
  
      No known copyright restrictions, released into the public domain.
  
      """
  
      return load("text.png")
  
  
  def checkerboard():
      """Checkerboard image.
  
      Checkerboards are often used in image calibration, since the
      corner-points are easy to locate.  Because of the many parallel
      edges, they also visualise distortions particularly well.
  
      """
      return load("chessboard_GRAY.png")
  
  
  def coins():
      """Greek coins from Pompeii.
  
      This image shows several coins outlined against a gray background.
      It is especially useful in, e.g. segmentation tests, where
      individual objects need to be identified against a background.
      The background shares enough grey levels with the coins that a
      simple segmentation is not sufficient.
  
      Notes
      -----
      This image was downloaded from the
      `Brooklyn Museum Collection
      <http://www.brooklynmuseum.org/opencollection/archives/image/617/image>`__.
  
      No known copyright restrictions.
  
      """
      return load("coins.png")
  
  
  def moon():
      """Surface of the moon.
  
      This low-contrast image of the surface of the moon is useful for
      illustrating histogram equalization and contrast stretching.
  
      """
      return load("moon.png")
  
  
  def page():
      """Scanned page.
  
      This image of printed text is useful for demonstrations requiring uneven
      background illumination.
  
      """
      return load("page.png")
  
  
  def clock():
      """Motion blurred clock.
  
      This photograph of a wall clock was taken while moving the camera in an
      aproximately horizontal direction.  It may be used to illustrate
      inverse filters and deconvolution.
  
      Released into the public domain by the photographer (Stefan van der Walt).
  
      """
      return load("clock_motion.png")
  