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# Image Processing

Octave can display images with the X Window System using the `xloadimage` program. You do not need to be running X in order to manipulate images, however, so some of these functions may be useful even if you are not able to view the results.

Loading images only works with Octave's image format (a file with a matrix containing the image data, and a matrix containing the colormap). Contributions of robust, well-written functions to read other image formats are welcome. If you can provide them, or would like to improve Octave's image processing capabilities in other ways, please contact @email{bug-octave@bevo.che.wisc.edu}.

Function File: colormap (map)
Function File: colormap ("default")
  Set the current colormap.

  `colormap (map)` sets the current colormap to map. The color map should be an n row by 3 column matrix. The columns contain red, green, and blue intensities respectively. All entries should be between 0 and 1 inclusive. The new colormap is returned.

  `colormap ("default")` restores the default colormap (a gray scale colormap with 64 entries). The default colormap is returned.

  With no arguments, `colormap` returns the current color map.

Function File: gray (n)
  Return a gray colormap with n entries corresponding to values from 0 to n. The argument n should be a scalar. If it is omitted, 64 is assumed.

Function File: [img, map] = gray2ind ()
  Convert a gray scale intensity image to an Octave indexed image.

Function File: image (x, zoom)
  Display a matrix as a color image. The elements of x are indices into the current colormap and should have values between 1 and the length of the colormap. If zoom is omitted, a value of 4 is assumed.

Function File: imagesc (x, zoom)
  Display a scaled version of the matrix x as a color image. The matrix is scaled so that its entries are indices into the current colormap. The scaled matrix is returned. If zoom is omitted, a value of 4 is assumed.

Function File: imshow (x, map)
Function File: imshow (x, n)
Function File: imshow (i, n)
Function File: imshow (r, g, b)
  Display images.

  `imshow (x)` displays an indexed image using the current colormap.

  `imshow (x, map)` displays an indexed image using the specified colormap.

  `imshow (i, n)` displays a gray scale intensity image.

  `imshow (r, g, b)` displays an RGB image.

Function File: ind2gray (x, map)
  Convert an Octave indexed image to a gray scale intensity image. If map is omitted, the current colormap is used to determine the intensities.

Function File: [r, g, b] = ind2rgb (x, map)
  Convert an indexed image to red, green, and blue color components. If map is omitted, the current colormap is used for the conversion.

Function File: [x, map] = loadimage (file)
  Load an image file and it's associated color map from the specified file. The image must be stored in Octave's image format.

Function File: rgb2ntsc (rgb)
  Image format conversion.

Function File: ntsc2rgb (yiq)
  Image format conversion.

Function File: ocean (n)
  Create color colormap. The argument n should be a scalar. If it is omitted, 64 is assumed.

Function File: [x, map] = rgb2ind (r, g, b)
  Convert and RGB image to an Octave indexed image.

Function File: saveimage (file, x, fmt, map)
  Save the matrix x to file in image format fmt. Valid values for fmt are
  `"img"`
    Octave's image format. The current colormap is also saved in the file.
  `"ppm"`
    Portable pixmap format.
  `"ps"`
    PostScript format. Note that images saved in PostScript format can not be read back into Octave with loadimage.

  If the fourth argument is supplied, the specified colormap will also be saved along with the image.

  Note: if the colormap contains only two entries and these entries are black and white, the bitmap ppm and PostScript formats are used. If the image is a gray scale image (the entries within each row of the colormap are equal) the gray scale ppm and PostScript image formats are used, otherwise the full color formats are used.

Built-in Variable: IMAGEPATH
  A colon separated list of directories in which to search for image files.

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