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25
26## -*- texinfo -*-
27## @deftypefn {} {@var{I} =} ind2gray (@var{x}, @var{map})
28## Convert a color indexed image to a grayscale intensity image.
29##
30## The image @var{x} must be an indexed image which will be converted using the
31## colormap @var{map}.  If @var{map} does not contain enough colors for the
32## image, pixels in @var{x} outside the range are mapped to the last color in
33## the map before conversion to grayscale.
34##
35## The output @var{I} is of the same class as the input @var{x} and may be
36## one of @code{uint8}, @code{uint16}, @code{single}, or @code{double}.
37##
38## Implementation Note: There are several ways of converting colors to
39## grayscale intensities.  This functions uses the luminance value obtained
40## from @code{rgb2gray} which is @code{I = 0.299*R + 0.587*G + 0.114*B}.
41## Other possibilities include the value component from @code{rgb2hsv} or
42## using a single color channel from @code{ind2rgb}.
43## @seealso{gray2ind, ind2rgb}
44## @end deftypefn
45
46function I = ind2gray (x, map)
47
48  if (nargin != 2)
49    print_usage ();
50  endif
51  [x, map] = ind2x ("ind2gray", x, map);
52
53  ## Convert colormap to luminance intensity values
54  map *= [0.29894; 0.58704; 0.11402];
55
56  ## Convert colormap to same class as that of input so that reshape
57  ## will produce output of the same type as the input.
58  cls = class (x);
59  if (isinteger (x))
60    ## if we later add support for int16 images, this will not work.  Look into
61    ## im2int16 from image package for such case
62    map *= intmax (cls);
63  elseif (strcmp (cls, "single"))
64    map = single (map);
65  endif
66
67  ## Replace indices in the input matrix with the indexed luminance value.
68  I = reshape (map(x(:)), size (x));
69
70endfunction
71
72
73%!shared i2g
74%! i2g = ind2gray (1:100, gray (100));
75%!
76%!assert (i2g, 0:1/99:1, eps)
77%!assert (gray2ind (i2g, 100), uint8 (0:99))
78
79## Test input validation
80%!error ind2gray ()
81%!error ind2gray (1)
82%!error ind2gray (1,2,3)
83%!error <X must be an indexed image> ind2gray (ones (3,3,3), jet (64))
84%!error <X must be an indexed image> ind2gray (1+i, jet (64))
85%!error <X must be an indexed image> ind2gray (sparse (1), jet (64))
86%!error <X must be an indexed image> ind2gray (1.1, jet (64))
87%!error <X must be an indexed image> ind2gray ({1}, jet (64))
88%!error <MAP must be a valid colormap> ind2gray (1, {1})
89%!error <MAP must be a valid colormap> ind2gray (1, 1+i)
90%!error <MAP must be a valid colormap> ind2gray (1, ones (2,2,2))
91%!error <MAP must be a valid colormap> ind2gray (1, ones (2,4))
92%!error <MAP must be a valid colormap> ind2gray (1, [-1])
93%!error <MAP must be a valid colormap> ind2gray (1, [2])
94
95%!warning <contains colors outside of colormap> ind2gray ([0 1 2], gray (5));
96%!warning <contains colors outside of colormap> ind2gray ([1 2 6], gray (5));
97%!warning <contains colors outside of colormap> ind2gray (uint8 ([1 2 5]), gray (5));
98