roihisteq(I, c, r)

function [Ieq, c, r, npix] = roihisteq(I, c, r)
%ROIHISTEQ Computes the localized histogram Equalization of an ROI in an image.
%   [Ieq, C, R, NPIX] = ROIHISTEQ(I, C, R) computes the localized histogram
%   equalization, Ieq, of a polygonal region of interest (ROI) in image I.  
%   The polygonal region is defined by the column and row coordinates of its
%   vertices, which are specified (sequentially) in vectors C and R,
%   respectively. If C and R were not supplied, the user may interactively 
%   draw an ROI on the image. All pixels of F must be >= 0. Parameter NPIX
%   is the number of pixels in the polygonal region. 
%
%   See also histeq, adapthisteq.
%
%   Example:
%   I = imread('tire.tif');
%   imshow(I);
%   [Ieq, c, r] = roihisteq(I);
%   subplot(1,2,1); imshow(I); title('Original Image');
%   hold on; line(c,r,'color','r');
%   subplot(1,2,2); imshow(Ieq); title('ROIHISTEQ Image');
%   hold on; line(c,r,'color','r');
%
%	Shanrong Zhang
%   Department of Radiology
%   University of Washington
%   03/13/2006
%   

% Generate the binary mask image.
if nargin == 3
    B = roipoly(I, c, r);
else
    [x,y,B,c,r] = roipoly;
end

Ieq = I;
% Compute the localized histogram equalization of the pixels in the ROI.
Ieq(B) = histeq(I(B));

% Obtain the number of pixels in the ROI if requested in the output.
if nargout > 3
   npix = sum(B(:)); 
end