(maxima.info)Functions and Variables for pictures

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53.3 Functions and Variables for pictures
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 -- Function: get_pixel (<pic>,<x>,<y>)
     Returns pixel from picture.  Coordinates <x> and <y> range from 0
     to 'width-1' and 'height-1', respectively.

 -- Function: make_level_picture
          make_level_picture (<data>)
          make_level_picture (<data>,<width>,<height>)

     Returns a levels <picture> object.  'make_level_picture (<data>)'
     builds the <picture> object from matrix <data>.
     'make_level_picture (<data>,<width>,<height>)' builds the object
     from a list of numbers; in this case, both the <width> and the
     <height> must be given.

     The returned <picture> object contains the following four parts:

       1. symbol 'level'
       2. image width
       3. image height
       4. an integer array with pixel data ranging from 0 to 255.
          Argument <data> must contain only numbers ranged from 0 to
          255; negative numbers are substituted by 0, and those which
          are greater than 255 are set to 255.

     Example:

     Level picture from matrix.
          (%i1) make_level_picture(matrix([3,2,5],[7,-9,3000]));
          (%o1)         picture(level, 3, 2, {Array:  #(3 2 5 7 0 255)})

     Level picture from numeric list.
          (%i1) make_level_picture([-2,0,54,%pi],2,2);
          (%o1)            picture(level, 2, 2, {Array:  #(0 0 54 3)})

 -- Function: make_rgb_picture (<redlevel>,<greenlevel>,<bluelevel>)
     Returns an rgb-coloured <picture> object.  All three arguments must
     be levels picture; with red, green and blue levels.

     The returned <picture> object contains the following four parts:

       1. symbol 'rgb'
       2. image width
       3. image height
       4. an integer array of length <3*width*height> with pixel data
          ranging from 0 to 255.  Each pixel is represented by three
          consecutive numbers (red, green, blue).

     Example:

          (%i1) red: make_level_picture(matrix([3,2],[7,260]));
          (%o1)           picture(level, 2, 2, {Array:  #(3 2 7 255)})
          (%i2) green: make_level_picture(matrix([54,23],[73,-9]));
          (%o2)           picture(level, 2, 2, {Array:  #(54 23 73 0)})
          (%i3) blue: make_level_picture(matrix([123,82],[45,32.5698]));
          (%o3)          picture(level, 2, 2, {Array:  #(123 82 45 33)})
          (%i4) make_rgb_picture(red,green,blue);
          (%o4) picture(rgb, 2, 2,
                        {Array:  #(3 54 123 2 23 82 7 73 45 255 0 33)})

 -- Function: negative_picture (<pic>)
     Returns the negative of a (<level> or <rgb>) picture.

 -- Function: picture_equalp (<x>,<y>)
     Returns 'true' in case of equal pictures, and 'false' otherwise.

 -- Function: picturep (<x>)
     Returns 'true' if the argument is a well formed image, and 'false'
     otherwise.

 -- Function: read_xpm (<xpm_file>)
     Reads a file in xpm and returns a picture object.

 -- Function: rgb2level (<pic>)
     Transforms an <rgb> picture into a <level> one by averaging the
     red, green and blue channels.

 -- Function: take_channel (<im>,<color>)
     If argument <color> is 'red', 'green' or 'blue', function
     'take_channel' returns the corresponding color channel of picture
     <im>.  Example:

          (%i1) red: make_level_picture(matrix([3,2],[7,260]));
          (%o1)           picture(level, 2, 2, {Array:  #(3 2 7 255)})
          (%i2) green: make_level_picture(matrix([54,23],[73,-9]));
          (%o2)           picture(level, 2, 2, {Array:  #(54 23 73 0)})
          (%i3) blue: make_level_picture(matrix([123,82],[45,32.5698]));
          (%o3)          picture(level, 2, 2, {Array:  #(123 82 45 33)})
          (%i4) make_rgb_picture(red,green,blue);
          (%o4) picture(rgb, 2, 2,
                        {Array:  #(3 54 123 2 23 82 7 73 45 255 0 33)})
          (%i5) take_channel(%,'green);  /* simple quote!!! */
          (%o5)           picture(level, 2, 2, {Array:  #(54 23 73 0)})