demo4
Contents
clear close all filename = '2013_0115_163116AA.JPG'; img = im2double(rgb2gray(imread(filename))); % crop rect from basics.m rect = [637.5 484.5 732 470]; g = imcrop(img,rect); imshow(g);
histogram, graythresh and im2bw
level = graythresh(I) computes a global threshold (level) that can be used to convert an intensity image to a binary image with im2bw. level is a normalized intensity value that lies in the range [0, 1].
%The graythresh function uses Otsu's method, which chooses the threshold % to minimize the intraclass variance of the black and white pixels. imhist(g); level = graythresh(g); hold on plot([level level],[0 1000],'k-','Linewidth',2); hold off fprintf('threshold %g\n',level);
threshold 0.521569
convert to bw image
BW = im2bw(g,level); imshow(BW);
bwconncomp
CC = bwconncomp(BW) returns the connected components CC found in BW. The binary image BW can have any dimension. CC is a structure with four fields.
CC = bwconncomp(~BW); disp(CC)
Connectivity: 8
ImageSize: [471 733]
NumObjects: 21
PixelIdxList: {1x21 cell}
regionprops
stats = regionprops(CC)
n = CC.NumObjects;
fprintf(' object area\n');
area = [stats.Area];
disp( [ [1:n]' area']);
stats =
21x1 struct array with fields:
Area
Centroid
BoundingBox
object area
1 6499
2 1667
3 424
4 112
5 1768
6 3196
7 3158
8 591
9 69
10 84
11 67258
12 1383
13 1405
14 1417
15 1397
16 1401
17 1397
18 1406
19 1416
20 1391
21 1369
centroids
centers = cat(1,stats.Centroid)
centers = 83.3664 398.0003 79.6449 278.6233 79.2712 201.8656 79.6696 131.2946 196.2104 131.6974 196.7225 263.3773 199.4427 383.0833 288.9577 140.1523 293.0870 280.2609 297.5000 400.5000 567.0909 317.5029 449.1518 87.0788 476.2007 87.2954 503.6824 87.4869 530.9485 88.0315 558.0214 88.4354 585.1160 88.3207 612.3122 88.3890 639.7507 89.4887 666.8749 89.1380 693.3448 90.3638
labelmatrix
L = labelmatrix(CC) creates a label matrix from the connected components structure CC returned by bwconncomp. The size of L is CC.ImageSize. The elements of L are integer values greater than or equal to 0.
L = labelmatrix(CC);
label2rgb
RGB = label2rgb(L) converts a label matrix into an RGB color image for the purpose of visualizing the labeled regions.
RGB = label2rgb(L); imshow(RGB);
select certain objects
idx = find(abs([stats.Area]-1400)<35); BW2 = ismember(L,idx); imshow(BW2);
select first four objects
imshow(ismember(L,1:4));
select based on eccentricity
s = regionprops(CC,'Eccentricity');
idx = find([s.Eccentricity]<0.3);
imshow(ismember(L,idx));
