ind2gray.m

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function b = ind2gray(a,cm)
%IND2GRAY Convert indexed image to intensity image.
%   I = IND2GRAY(X,MAP) converts the image X with colormap MAP
%   to an intensity image I. IND2GRAY removes the hue and
%   saturation information while retaining the luminance.
%
%   Class Support
%   -------------
%   X can be of class uint8 or double. I is of class double.
%
%   Example
%   -------
%       load trees
%       I = ind2gray(X,map);
%       imshow(X,map), figure, imshow(I)
%
%   See also GRAY2IND, IMSHOW, RGB2NTSC.

%   Clay M. Thompson 9-10-92
%   Copyright 1993-1998 The MathWorks, Inc.  All Rights Reserved.
%   $Revision: 5.6 $  $Date: 1997/11/24 15:35:39 $

if isa(a, 'uint8')
    a = double(a)+1;    % Switch to one based indexing
end

error(nargchk(2,2,nargin));

% Convert CM to NTSC coordinates
ntsc = rgb2ntsc(cm);

% Make sure A is in the range from 1 to size(cm,1)
a = max(1,min(a,size(cm,1)));

% Define B
b = zeros(size(a));
b(:) = ntsc(a,1); % Gray image is first component