octave:scripts/image/rgb2hsv.m

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scripts/image/rgb2hsv.m

changeset 10289:	4b124317dc38
parent:	4fbfce35012a
author:	John W. Eaton <jwe@octave.org>
date:	Tue Feb 09 20:58:55 2010 -0500 (30 minutes ago)
permissions:	-rw-r--r--
description:	base_properties::set_children: account for hidden children
     1## Copyright (C) 1999, 2000, 2001, 2002, 2004, 2005, 2006, 2007, 2008
     2##               Kai Habel
     3##
     4## This file is part of Octave.
     5##
     6## Octave is free software; you can redistribute it and/or modify it
     7## under the terms of the GNU General Public License as published by
     8## the Free Software Foundation; either version 3 of the License, or (at
     9## your option) any later version.
    10##
    11## Octave is distributed in the hope that it will be useful, but
    12## WITHOUT ANY WARRANTY; without even the implied warranty of
    13## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    14## General Public License for more details.
    15##
    16## You should have received a copy of the GNU General Public License
    17## along with Octave; see the file COPYING.  If not, see
    18## <http://www.gnu.org/licenses/>.
    19
    20## -*- texinfo -*-
    21## @deftypefn {Function File} {@var{hsv_map} =} rgb2hsv (@var{rgb_map})
    22## Transform a colormap or image from the rgb space to the hsv space.
    23##
    24## A color n the RGB space consists of the red, green and blue intensities.
    25##
    26## In the HSV space each color is represented by their hue, saturation
    27## and value (brightness).  Value gives the amount of light in the color.
    28## Hue describes the dominant wavelength. 
    29## Saturation is the amount of Hue mixed into the color.
    30## @seealso{hsv2rgb}
    31## @end deftypefn
    32
    33## Author: Kai Habel <kai.habel@gmx.de>
    34## Adapted-by: jwe
    35
    36function hsval = rgb2hsv (rgb)
    37
    38  if (nargin != 1)
    39    print_usage ();
    40  endif
    41
    42  ## If we have an image convert it into a color map.
    43  if (ismatrix (rgb) && ndims (rgb) == 3)
    44    is_image = true;
    45    Sz = size (rgb);
    46    rgb = [rgb(:,:,1)(:), rgb(:,:,2)(:), rgb(:,:,3)(:)];
    47    ## Convert to a double image.
    48    if (isinteger (rgb))
    49      C = class (rgb);
    50      low = double (intmin (C));
    51      high = double (intmax (C));
    52      rgb = (double (rgb) - low) / (high - low);
    53    endif
    54  else
    55    is_image = false;
    56  endif
    57
    58  if (! ismatrix (rgb) || columns (rgb) != 3)
    59    error ("rgb2hsv: argument must be a matrix of size n x 3");
    60  endif
    61
    62  ## get the max and min
    63  s = min (rgb')';
    64  v = max (rgb')';
    65
    66  ## set hue to zero for undefined values (gray has no hue)
    67  h = zeros (size (v));
    68  notgray = (s != v);
    69    
    70  ## blue hue
    71  idx = (v == rgb(:,3) & notgray);
    72  if (any (idx))
    73    h(idx) = 2/3 + 1/6 * (rgb(idx,1) - rgb(idx,2)) ./ (v(idx) - s(idx));
    74  endif
    75
    76  ## green hue
    77  idx = (v == rgb(:,2) & notgray);
    78  if (any (idx))
    79    h(idx) = 1/3 + 1/6 * (rgb(idx,3) - rgb(idx,1)) ./ (v(idx) - s(idx));
    80  endif
    81
    82  ## red hue
    83  idx = (v == rgb(:,1) & notgray);
    84  if (any (idx))
    85    h(idx) =       1/6 * (rgb(idx,2) - rgb(idx,3)) ./ (v(idx) - s(idx));
    86  endif
    87
    88  ## correct for negative red
    89  idx = (h < 0);
    90  h(idx) = 1+h(idx);
    91
    92  ## set the saturation
    93  s(! notgray) = 0;
    94  s(notgray) = 1 - s(notgray) ./ v(notgray);
    95
    96  hsval = [h, s, v];
    97  
    98  ## If input was an image, convert it back into one.
    99  if (is_image)
   100    hsval = reshape (hsval, Sz);
   101  endif
   102
   103endfunction