I can't open .mlx files in any practical way, so this isn't really a direct answer. I'm just going to point out that histeq() can always be opened and inspected. Alternatively, MIMT contains a replacement that may (or may not) be easier to read, though it relies on other MIMT tools. It should still be fairly easy to read between the lines though.
function [outpict TF] = histeqFB(inpict,varargin)
% OUTPICT=HISTEQFB(INPICT,{NBINS})
% OUTPICT=HISTEQFB(INPICT,{HGRAM})
% [OUTPICT TF]=HISTEQFB( ... )
% Adjust the contrast of an image such that its intensity distribution conforms to that described
% by a given histogram. If no histogram is given explicitly, a flat (uniform) histogram of either
% a default or user-specified number of bins is used.
%
% Optionally, the 1D transfer function TF mapping the input image to the output image can be returned.
%
% This is a passthrough to the IPT function histeq(), with an internal fallback implementation
% to help remove the dependency of MIMT tools on the Image Processing Toolbox. As with other fallback
% tools, performance without IPT may be degraded or otherwise different due to the methods used.
%
% INPICT is a single-channel image of any standard image class.
% While the IPT tools support indexed images, the fallback tools do not.
% NBINS optionally specifies how many bins should be used for flat histograms (default 64)
% HGRAM optionally specifies the target output distribution explicitly
%
% Output image class is inherited from INPICT
% TF class is double
%
% Webdocs: http://mimtdocs.rf.gd/manual/html/histeqFB.html
% See also: histeq, imhist, imhistFB, imlnc
% IF IPT IS INSTALLED, USE IT
if hasipt()
[outpict TF] = histeq(inpict,varargin{:});
return;
end
% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
nin = 256; % internal default
if numel(varargin) == 0
% HISTEQFB(I)
nout = 64;
hgram = ones([1 nout])*numel(inpict)/nout;
else
if size(varargin{1},2) == 3
% HISTEQFB(IX,MAP)
% HISTEQFB(IX,MAP,HGRAM)
error('HISTEQFB: fallback methods to not support indexed images')
elseif numel(varargin{1}) == 1
% HISTEQFB(I,NBINS)
nout = round(varargin{1});
hgram = ones([1 nout])*numel(inpict)/nout;
else
% HISTEQFB(I,HGRAM)
hgram = round(varargin{1});
hgram = hgram*numel(inpict)/sum(hgram); % normalize wrt sum
nout = numel(hgram);
if ~isvector(hgram)
error('HISTEQFB: HGRAM is supposed to be a vector')
end
end
end
% get input histogram
hgramin = imhistFB(inpict,nin)'; % same as IPT imhist()
% calculate cumulative hgram sums
incsum = cumsum(hgramin);
outcsum = cumsum(hgram*numel(inpict)/sum(hgram));
% generate TF mapping inpict to outpict
numin = numel(inpict);
tol = ones([nout 1])*min([hgramin(1:nin-1) 0; 0 hgramin(2:nin)])/2;
err = (outcsum(:)*ones([1 nin])-ones([nout 1])*incsum(:)')+tol;
orv = find(err < -numin*sqrt(eps));
if ~isempty(orv)
err(orv) = numin*ones(size(orv));
end
[~,idx] = min(err); % location of minimum error
TF = (idx-1)/(nout-1); % normalize
% this replicates the functionality of grayxformmex
[inpict inclass] = imcast(inpict,'double'); % imcast() replaces im2double(),im2uint8(), etc
inpict = min(max(inpict,0),1);
outpict = interp1(linspace(0,1,numel(TF)),TF,inpict,'nearest');
outpict = imcast(outpict,inclass);
I doubt you need to make your implementation mimic all the different functionality of histeq(), so some simplification is probably due.
