此程序实现用Hough变换和数学形态学变换对二值车牌图像进行水平倾斜校正

function lines = houghlines(f,theta,rho,rr,cc,fillgap,minlength) %HOUGHLINES Extract line segments based on the Hough transform. % LINES = HOUGHLINES(F, THETA, RHO, RR, CC, FILLGAP, MINLENGTH) % extracts line segments in the image F associated with particular % bins in a Hough transform. THETA and RHO are vectors returned by % function HOUGH. Vectors RR and CC specify the rows and columns % of the Hough transform bins to use in searching for line % segments. If HOUGHLINES finds two line segments associated with % the same Hough transform bin that are separated by less than % FILLGAP pixels, HOUGHLINES merges them into a single line % segment. FILLGAP defaults to 20 if omitted. Merged line % segments less than MINLENGTH pixels long are discarded. % MINLENGTH defaults to 40 if omitted. % % LINES is a structure array whose length equals the number of % merged line segments found. Each element of the structure array % has these fields: % % point1 End-point of the line segment; two-element vector % point2 End-point of the line segment; two-element vector % length Distance between point1 and point2 % theta Angle (in degrees) of the Hough transform bin % rho Rho-axis position of the Hough transform bin % Copyright 2002-2004 R. C. Gonzalez, R. E. Woods, & S. L. Eddins % Digital Image Processing Using MATLAB, Prentice-Hall, 2004 % $Revision: 1.4 $ $Date: 2003/10/26 22:34:10 $ if nargin < 6 fillgap = 20; end if nargin < 7 minlength = 40; end numlines = 0; lines = struct; for k = 1:length(rr) rbin = rr(k); cbin = cc(k); % Get all pixels associated with Hough transform cell. [r, c] = houghpixels(f, theta, rho, rbin, cbin); if isempty(r) continue end % Rotate the pixel locations about (1,1) so that they lie % approximately along a vertical line. omega = (90 - theta(cbin)) * pi / 180; T = [cos(omega) sin(omega); -sin(omega) cos(omega)]; xy = [r - 1 c - 1] * T; x = sort(xy(:,1)); % Find the gaps larger than the threshold. diff_x = [diff(x); Inf]; idx = [0; find(diff_x > fillgap)]; for p = 1:length(idx) - 1 x1 = x(idx(p) + 1); x2 = x(idx(p + 1)); linelength = x2 - x1; if linelength >= minlength point1 = [x1 rho(rbin)]; point2 = [x2 rho(rbin)]; % Rotate the end-point locations back to the original % angle. Tinv = inv(T); point1 = point1 * Tinv; point2 = point2 * Tinv; numlines = numlines + 1; lines(numlines).point1 = point1 + 1; lines(numlines).point2 = point2 + 1; lines(numlines).length = linelength; lines(numlines).theta = theta(cbin); lines(numlines).rho = rho(rbin); end end end