%  perspRect - this function let the user choose a perspectively distorted 
%              rectangular region and rectified the image back to a
%              rectangle.
%
%  Usage:       imRect = perspRect(im,sze,option)
%
%  Arguments:   im      - image to be rectified
%               sze     - size of the output image, [width,height] in pixel
%               option  - 1: rectify the whole image
%                         2: rectify the selected region in the image
%                         3: rectify the selected region and crop it (default)
%
%  Returns:     imRect  - the rectified image
%
%  Author: 
%  Tzu Yen Wong
%  wongt AT csse DOT uwa DOT edu DOT au
%  Department of Computer Science & Software Engineering
%  The University of Western Australia
%
%  Date:        March 2006

function imRect = perspRect(im,sze,option)

eval('option;','option=3;')
eval('sze;','sze=[300 300];')

% get the distorted rectangular area
show(im)
title('digitize 4 corner points')
[x,y]=getline('close'); 
pts1 = [x(1:4),y(1:4)]';
hold on, plot([x(1:4);x(1)],[y(1:4);y(1)],'-ro')
title('digitization of points succeeded!')
drawnow

% get the output rectangle 
width = sze(1);
height = sze(2);
pts2 = [1 width width 1; 1 1 height height];
    
% calculate the perspective transformation 
T = homography2d([pts1; ones(1,4); pts2; ones(1,4)]);

rg1 = getRegion(pts1,1);

warning off
if option==1,
    [imw,newT] = imtrans(im,T);
elseif option>=2,
    [imw,newT] = imtrans(im,T,rg1);
else
    warning('invalid option, default used')
end
warning on

pts1w = trans(inv(newT)*T,pts1);

% crop out the rectangular area 
if option==3,
    xmin = min(pts1w(1,:));
    ymin = min(pts1w(2,:));
    ww = max(pts1w(1,:)) - xmin + 1;
    hh = max(pts1w(2,:)) - ymin + 1;
    imw = imcrop(imw,[xmin ymin ww hh]);
end

show(imw)
imRect = imw;
if option < 3,
    hold on, 
    polyplot(pts1w,'ro-');
end



function region = getRegion(pts,rounded)
    minrow = min(pts(2,:));
    maxrow = max(pts(2,:));
    mincol = min(pts(1,:));
    maxcol = max(pts(1,:));

    region = [minrow maxrow mincol maxcol];
    if rounded,
        region = [floor(minrow) ceil(maxrow) floor(mincol) ceil(maxcol)];
    end
return