dither.m

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function imout=dither(arg1,arg2,arg3,arg4,arg5,arg6)
%DITHER Convert image using dithering.
%   X = DITHER(RGB,MAP) creates an indexed image approximation of
%   the RGB image in the array RGB by dithering the colors in
%   colormap MAP.
%
%   X = DITHER(RGB,MAP,Qm,Qe) creates an indexed image from RGB,
%   specifying the parameters Qm and Qe. Qm specifies the number
%   of quantization bits to use along each color axis for the
%   inverse color map, and Qe specifies the number of
%   quantization bits to use for the color space error
%   calculations.  If Qe < Qm, dithering cannot be performed and
%   an undithered indexed image is returned in X.  If you omit
%   these parameters, DITHER uses the default values Qm = 5, 
%   Qe = 8.
%
%   BW = DITHER(I) converts the intensity image in the matrix I
%   to the binary image BW by dithering.
%
%   Class Support
%   -------------
%   The input image (RGB or I) can be of class double or
%   uint8. All other input arguments must be of class double. The
%   output image (X or BW) is of class uint8 if it is a binary
%   image or if it an indexed image with 256 or fewer colors;
%   otherwise its class is double.
%
%   See also RGB2IND.

%   Joseph M. Winograd 7-93
%   Copyright 1993-1998 The MathWorks, Inc.  All Rights Reserved.
%   $Revision: 5.11 $  $Date: 1997/11/24 15:34:34 $

%   References: 
%      R. W. Floyd and L. Steinberg, "An Adaptive Algorithm for
%         Spatial Gray Scale," International Symposium Digest of Technical
%         Papers, Society for Information Displays, 36.  1975.
%      Spencer W. Thomas, "Efficient Inverse Color Map Computation",
%         Graphics Gems II, (ed. James Arvo), Academic Press: Boston.
%         1991. (includes source code)

if nargin < 1,
  error('Need input arguments');
end

threeD = (ndims(arg1)==3); % Determine if input includes a 3-D array

if threeD,
  
  if nargin < 4
    arg4 = 8; % DEFAULT:  If this is changed, modify the other occurrence
            %                for NOT(threeD).
  end

  if nargin < 3
    arg3 = 5; % DEFAULT:  See note above.
  end

  if nargin==1
    error('Wrong number of input parameters.');
  else
    if (~isa(arg1,'uint8'))
      arg1 = uint8(round(255*arg1));
    end  
    im = ditherc(arg1(:,:,1),arg1(:,:,2),arg1(:,:,3),arg2,arg3,arg4);
  end

  map = arg2;

else % R, G, and B are passed in as separate variables.

  error( nargchk( 1, 6, nargin ) );

  if nargin < 6
    arg6 = 8;        % DEFAULT
  end

  if nargin < 5
    arg5 = 5;        % DEFAULT
  end

  if nargin==1
    if (~isa(arg1,'uint8'))
      arg1 = uint8(round(255*arg1));
    end
    im = im2bw(ditherc(arg1,arg1,arg1,gray(2),arg5,arg6),gray(2));
  elseif nargin==2 | nargin==3,
    error('Wrong number of input parameters.');
  else
    if (~isa(arg1,'uint8'))
      arg1 = uint8(round(255*arg1));
    end
    if (~isa(arg2,'uint8'))
      arg2 = uint8(round(255*arg2));
    end
    if (~isa(arg3,'uint8'))
      arg3 = uint8(round(255*arg3));
    end
    im = ditherc(arg1,arg2,arg3,arg4,arg5,arg6);
    map = arg4;
  end

end



if nargout==0,
  if (nargin==1 & ~threeD), imshow(im,2), else, imshow(im,map), end
  return
end
imout = im;