[問題] Gonzalez 書中hough transform code問題已回收
想請問板上的各位大大
小弟在閱讀Gonzalez的書中 hough transform時, 有一句程式碼一直看不懂
懇請板上神人給些意見
以下附上 hough transform 的源代碼, 另小弟將看不懂的地方以紅色highlight 起來
function [h, theta, rho] = hough(f, dtheta, drho)
%HOUGH Hough transform.
% [H, THETA, RHO] = HOUGH(F, DTHETA, DRHO) computes the Hough
% transform of the image F. DTHETA specifies the spacing (in
% degrees) of the Hough transform bins along the theta axis. DRHO
% specifies the spacing of the Hough transform bins along the rho
% axis. H is the Hough transform matrix. It is NRHO-by-NTHETA,
% where NRHO = 2*ceil(norm(size(F))/DRHO) - 1, and NTHETA =
% 2*ceil(90/DTHETA). Note that if 90/DTHETA is not an integer, the
% actual angle spacing will be 90 / ceil(90/DTHETA).
%
% THETA is an NTHETA-element vector containing the angle (in
% degrees) corresponding to each column of H. RHO is an
% NRHO-element vector containing the value of rho corresponding to
% each row of H.
%
% [H, THETA, RHO] = HOUGH(F) computes the Hough transform using
% DTHETA = 1 and DRHO = 1.
% 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 22:33:44 $
if nargin < 3
drho = 1;
end
if nargin < 2
dtheta = 1;
end
f = double(f);
[M,N] = size(f);
theta = linspace(-90, 0, ceil(90/dtheta) + 1);
theta = [theta -fliplr(theta(2:end - 1))];
ntheta = length(theta);
D = sqrt((M - 1)^2 + (N - 1)^2);
q = ceil(D/drho);
nrho = 2*q - 1;
rho = linspace(-q*drho, q*drho, nrho);
[x, y, val] = find(f);
x = x - 1; y = y - 1;
% Initialize output.
h = zeros(nrho, length(theta));
% To avoid excessive memory usage, process 1000 nonzero pixel
% values at a time.
for k = 1:ceil(length(val)/1000)
first = (k - 1)*1000 + 1;
last = min(first+999, length(x));
x_matrix = repmat(x(first:last), 1, ntheta);
y_matrix = repmat(y(first:last), 1, ntheta);
val_matrix = repmat(val(first:last), 1, ntheta);
theta_matrix = repmat(theta, size(x_matrix, 1), 1)*pi/180;
rho_matrix = x_matrix.*cos(theta_matrix) + ...
y_matrix.*sin(theta_matrix);
slope = (nrho - 1)/(rho(end) - rho(1));
rho_bin_index = round(slope*(rho_matrix - rho(1)) + 1);
theta_bin_index = repmat(1:ntheta, size(x_matrix, 1), 1);
% Take advantage of the fact that the SPARSE function, which
% constructs a sparse matrix, accumulates values when input
% indices are repeated. That抯 the behavior we want for the
% Hough transform. We want the output to be a full (nonsparse)
% matrix, however, so we call function FULL on the output of
% SPARSE.
h = h + full(sparse(rho_bin_index(:), theta_bin_index(:), ...
val_matrix(:), nrho, ntheta));
end
想請問各位大大的是...為什麼要計算Slope這個變數,以及為什麼rho_bin_index這個變數
要乘上slope ??
懇請各位大大幫我解釋一下...
--
※ 發信站: 批踢踢實業坊(ptt.cc)
◆ From: 58.115.155.217
※ 編輯: darlpower 來自: 58.115.155.217 (09/16 22:53)