matlab polar2.m,ilogpolar.m · zigzag2015/machinevision-toolbox-matlab - Gitee.com

%ILOGPOLAR Log-polar transform

%

% OUT = ILOGPOLAR(IM, OPTIONS) is a log-polar representation of the

% image IM. Every pixel in IM is rendered at the coordinate (log(r), theta)

% in the output image OUT (WxH), and where (r,theta) is the polar coordinate

% of the correspondingin pixel in the image IM.

%

% [OUT,VTH,VLOGP] = ILOGPOLAR(IM, OPTIONS) as above but also returns

% vectors VTH (1xW) and VLOGP (1xH) with the correspond theta and log(r)

% values.

%

% ILOGPOLAR(IM, OPTIONS) as above but the image is displayed.

%

% Options::

% 'centre',C Coordinate of the point from which radial distance is

% computed (default centre of the image).

% 'ntheta',N Number of pixels in the theta direction (default 400).

% 'nlogp',N Number of pixels in the log-p direction (default 400).

%

% Notes::

% - The log-polar image has the properties that:

% - a rotation of the image about the centre point becomes a horizontal shift.

% - a scale of the image (zoom) becomes a vertical shift.

%

% References::

% - http://en.wikipedia.org/wiki/Log-polar_coordinates

%

% See also IWARP.

function [out, vth, vlogp] = ilogpolar(im, varargin)

opt.centre = isize(im)/2;

opt.ntheta = 400;

opt.nlogp = 400;

opt = tb_optparse(opt, varargin);

% create coordinate matrices for the output image

[U,V] = imeshgrid(opt.ntheta, opt.nlogp);

% scale U coordinate to range 0 to 2pi

th = U/numcols(U) * 2*pi;

% compute the maximum radius

[w h] = isize(im);

corners = [1 w w 1; 1 1 h h];

d = colnorm( bsxfun(@minus, corners, opt.centre(:)));

% scale V coordinate to range 0 to max(log(radius))

logp = V/numrows(V) * log(max(d));

% now compute inverse log-polar transform, which is very elegant

% using complex numbers

XY = exp(logp + i*th) + opt.centre(1) + i*opt.centre(2);

% now warp

out_ = iwarp(im, real(XY), imag(XY) );

if nargout == 0

idisp(out_, 'ynormal', 'xydata', {th(1,:), logp(:,1)} );

xlabel('\theta'); ylabel('log(r)');

else

out = out_;

if nargout > 1

vth = th(1,:);

end

if nargout > 2

vlogp = logp(:,1);

end

end

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