## diameter.m ( File view )

• By yueqiaohuayuan 2014-11-17
• View(s)：3508
• Point(s)： 3
```			function s = diameter(L)
%DIAMETER Measure diameter and related properties of image regions.
%   S = DIAMETER(L) computes the diameter, the major axis endpoints,
%   the minor axis endpoints, and the basic rectangle of each labeled
%   region in the label matrix L. Positive integer elements of L
%   correspond to different regions. For example, the set of elements
%   of L equal to 1 corresponds to region 1; the set of elements of L
%   equal to 2 corresponds to region 2; and so on.  S is a structure
%   array of length max(L(:)). The fields of the structure array
%   include:
%
%     Diameter
%     MajorAxis
%     MinorAxis
%     BasicRectangle
%
%   The Diameter field, a scalar, is the maximum distance between any
%   two pixels in the corresponding region.
%
%   The MajorAxis field is a 2-by-2 matrix.  The rows contain the row
%   and column coordinates for the endpoints of the major axis of the
%   corresponding region.
%
%   The MinorAxis field is a 2-by-2 matrix.  The rows contain the row
%   and column coordinates for the endpoints of the minor axis of the
%   corresponding region.
%
%   The BasicRectangle field is a 4-by-2 matrix.  Each row contains
%   the row and column coordinates of a corner of the
%   region-enclosing rectangle defined by the major and minor axes.
%
%   of Digital Image Processing, by Gonzalez and Woods, 2nd edition,
%   Prentice Hall.

%   Copyright 2002-2004 R. C. Gonzalez, R. E. Woods, & S. L. Eddins
%   Digital Image Processing Using MATLAB, Prentice-Hall, 2004
%   \$Revision: 1.6 \$  \$Date: 2003/11/21 14:31:09 \$

s = regionprops(L, {
'Image', 'BoundingBox'
});

for k = 1:length(s)
[s(k).Diameter, s(k).MajorAxis, perim_r, perim_c] = ...
compute_diameter(s(k));
[s(k).BasicRectangle, s(k).MinorAxis] = ...
compute_basic_rectangle(s(k), perim_r, perim_c);
end

%-------------------------------------------------------------------%
function [d, majoraxis, r, c] = compute_diameter(s)
%   [D, MAJORAXIS, R, C] = COMPUTE_DIAMETER(S) computes the diameter
%   and major axis for the region represented by the structure S. S
%   must contain the fields Image and BoundingBox.  COMPUTE_DIAMETER
%   also returns the row and column coordinates (R and C) of the
%   perimeter pixels of s.Image.

% Compute row and column coordinates of perimeter pixels.
[r, c] = find(bwperim(s.Image));
r = r(:);
c = c(:);
[rp, cp] = prune_pixel_list(r, c);

num_pixels = length(rp);
switch num_pixels
case 0
d = -Inf;
majoraxis = ones(2, 2);

case 1
d = 0;
majoraxis = [rp cp; rp cp];

case 2
d = (rp(2) - rp(1))^2 + (cp(2) - cp(1))^2;
majoraxis = [rp cp];

otherwise
% Generate all combinations of 1:num_pixels taken two at at time.
% Method suggested by Peter Acklam.
[idx(:, 2) idx(:, 1)] = find(tril(ones(num_pixels), -1));
rr = rp(idx);
cc = cp(idx);

dist_squared = (rr(:, 1) - rr(:, 2)).^2 + ...
(cc(:, 1) - cc(:, 2)).^2;
[max_dist_squared, idx] = max(dist_squared);
majoraxis = [rr(idx,:)' cc(idx,:)'];

d = sqrt(max_dist_squared);

upper_image_row = s.BoundingBox(2) + 0.5;
left_image_col = s.BoundingBox(1) + 0.5;

majoraxis(:, 1) = majoraxis(:, 1) + upper_image_row - 1;
majoraxis(:, 2) = majoraxis(:, 2) + left_image_col - 1;
end

%-------------------------------------------------------------------%
function [basicrect, minoraxis] = compute_basic_rectangle(s, ...
perim_r, perim_c)
%   [BASICRECT,MINORAXIS] = COMPUTE_BASIC_RECTANGLE(S, PERIM_R,
%   PERIM_C) computes the basic rectangle and the minor axis
%   end-points for the region represented by the structure S.  S must
%   contain the fields Image, BoundingBox, MajorAxis, and
%   Diameter. PERIM_R and PERIM_C are the row and column coordinates
%   of perimeter of s.Image. BASICRECT is a 4-by-2 matrix, each row
%   of which contains the row and column coordinates of one corner of
%   the basic rectangle.

% Compute the orientation of the major axis.
theta = atan2(s.MajorAxis(2, 1) - s.MajorAxis(1, 1), ...
s.MajorAxis(2, 2) - s.MajorAxis(1, 2));

% Form rotation matrix.
T = [cos(theta) sin(theta); -sin(theta) cos(theta)];

...
...
```
...
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Contents.m5.98 kB2012-02-29|09:51
average.m651.00 B2012-02-29|09:51
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### diameter.m (160.12 kB)

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