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mat2im

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08 Jan 2010 (Updated )

Convert 2D matrix to a 3D image matrix as used by the image processing toolbox

im=mat2im(mat,cmap,limits)
function im=mat2im(mat,cmap,limits)
% mat2im - convert to rgb image
%
% function im=mat2im(mat,cmap,maxVal)
%
% PURPOSE
% Uses vectorized code to convert matrix "mat" to an m-by-n-by-3
% image matrix which can be handled by the Mathworks image-processing
% functions. The the image is created using a specified color-map
% and, optionally, a specified maximum value. Note that it discards
% negative values!
%
% INPUTS
% mat     - an m-by-n matrix  
% cmap    - an m-by-3 color-map matrix. e.g. hot(100). If the colormap has 
%           few rows (e.g. less than 20 or so) then the image will appear 
%           contour-like.
% limits  - by default the image is normalised to it's max and min values
%           so as to use the full dynamic range of the
%           colormap. Alternatively, it may be normalised to between
%           limits(1) and limits(2). Nan values in limits are ignored. So
%           to clip the max alone you would do, for example, [nan, 2]
%          
%
% OUTPUTS
% im - an m-by-n-by-3 image matrix  
%
%
% Example 1 - combine multiple color maps on one figure 
% clf, colormap jet, r=rand(40);
% subplot(1,3,1),imagesc(r), axis equal off , title('jet')
% subplot(1,3,2),imshow(mat2im(r,hot(100))) , title('hot')
% subplot(1,3,3),imshow(mat2im(r,summer(100))), title('summer')
% colormap winter %changes colormap in only the first panel
%
% Example 2 - clipping
% p=peaks(128); J=jet(100);
% subplot(2,2,1), imshow(mat2im(p,J)); title('Unclipped')
% subplot(2,2,2), imshow(mat2im(p,J,[0,nan])); title('Remove pixels <0')
% subplot(2,2,3), imshow(mat2im(p,J,[nan,0])); title('Remove pixels >0')
% subplot(2,2,4), imshow(mat2im(p,J,[-1,3])); title('Plot narrow pixel range')
%
% Rob Campbell - April 2009
%
% See Also: ind2rgb, imadjust


%Check input arguments
error(nargchk(2,3,nargin));

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

if ~isnumeric(cmap)
    error('cmap must be a colormap, such as jet(100)')
end


%Clip if desired
L=length(cmap);
if nargin==3 && length(limits)==1
    warning('limits should be vector of length of 2. Assuming a max value was specified.')
    limits=[nan,limits];
end


if nargin==3
    minVal=limits(1);
    if isnan(minVal), minVal=min(mat(:)); end    
    mat(mat<minVal)=minVal;
    
    maxVal=limits(2);
    if isnan(maxVal), maxVal=max(mat(:)); end
    mat(mat>maxVal)=maxVal;        
else
minVal=min(mat(:));
maxVal=max(mat(:));
end


%Normalise 
mat=mat-minVal;
mat=(mat/(maxVal-minVal))*(L-1);
mat=mat+1;


%convert to indecies 
mat=round(mat); 


%Vectorised way of making the image matrix 
im=reshape(cmap(mat(:),:),[size(mat),3]);

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