Matlab 代码中跟踪边界的移动？

Question

I am trying to trace boundaries of objects using a manual ROI selection and to plot there outlines back on the original image in grayscale. I noticed that I have a shift of the outline compered to the original object location. Why? did I missed something in my code?

Code:

close all;
clear all;
clc;
I = imread('pillsetc.png');
figure('Name','pillsetc');
imshow(I)
  
x1 = 50;
y1 = 200
Iroi = imcrop(I,[x1,y1,400,150]);


GrayRoi = rgb2gray(Iroi);
figure('Name','pillsetcGrayCrop');
imshow(GrayRoi);
BWRoi = imbinarize(GrayRoi);
BWRoi = bwareaopen(BWRoi, 10);
BWRoi = imfill(BWRoi,'holes');
[B,L] = bwboundaries(BWRoi,'noholes');
            
stat = regionprops(L, 'Centroid');
figure('Name','pillsetcCropBoundaries');
imshow(rgb2gray(I));
hold on;
             
for k = 1 :numel(stat)
    b = B{k};
    c = stat(k).Centroid;
    plot(b(:,2)+x1, b(:,1)+y1,'r');
end

Answer 1

Looks like your image is not as binary as regionprops prefers. The regionprops function appears to be Left-to-Right raster scanning for the brightest to start and darkest to stop, and delays any action on gradients.

To put it simply:

• Upon the brightest (similar to white) of a gradient, selection starts
• Upon the darkest (similar to black) of a gradient, selection ends

So if you make make the dark background blur together to the same darkest level and then spike any non-dark to the brightest foreground (any grey above bottom couple darkest levels is set to white) before processing with regionprops, you might get better outlines.

Answer 2

1.- Use MATLAB command bwboundaries

close all;clear all;clc

A=imread('001.jpg');
A2=rgb2gray(A);

BW = imbinarize(A2);

[B,L] = bwboundaries(BW,'noholes');

figure;
imshow(label2rgb(L, @jet, [.5 .5 .5]))
hold on
for k = 1:length(B)
   boundary = B{k};
   plot(boundary(:,2), boundary(:,1), 'w', 'LineWidth', 2)
end

Without the colouring generated with label2rgb

figure;
imshow(L);
hold on
for k = 1:length(B)
   boundary = B{k};
   plot(boundary(:,2), boundary(:,1), 'w', 'LineWidth', 2)
end

2.- Numbering all found boundaries

[B,L,N,A] = bwboundaries(BW);
figure;
imshow(BW); hold on;
colors=['b' 'g' 'r' 'c' 'm' 'y'];
for k=1:length(B)
  boundary = B{k};
  cidx = mod(k,length(colors))+1;
  plot(boundary(:,2), boundary(:,1),colors(cidx),'LineWidth',2);

  rndRow = ceil(length(boundary)/(mod(rand*k,7)+1));
  col = boundary(rndRow,2); row = boundary(rndRow,1);
  h = text(col+1, row-1, num2str(L(row,col)));
  set(h,'Color',colors(cidx),'FontSize',14,'FontWeight','bold');
end

Too many elements

B 
 30×1 cell array
 {446×2 double}
 {146×2 double}
 {  3×2 double}
 {776×2 double}
 {150×2 double}
 {343×2 double}
 {  2×2 double}
 {  2×2 double}
 {408×2 double}
  ...
 {  2×2 double}
 {543×2 double}
 {  2×2 double}
 {  2×2 double}
 {  2×2 double}
 {441×2 double}
 {  2×2 double}
 {  2×2 double}



size(B)
 =
 30     1

3.- Removing small elements

th1=100;   % threshold
B2={}
for k=1:1:size(B,1)
    B0=B{k};
    if size(B0,1)>th1
        B2=[B2 B0];
    end
end

figure;
imshow(BW); hold on;
colors=['b' 'g' 'r' 'c' 'm' 'y'];
for k=1:length(B2)
  boundary = B2{k};
  cidx = mod(k,length(colors))+1;
  plot(boundary(:,2), boundary(:,1),colors(cidx),'LineWidth',2);

  rndRow = ceil(length(boundary)/(mod(rand*k,7)+1));
  col = boundary(rndRow,2); row = boundary(rndRow,1);
  h = text(col+1, row-1, num2str(L(row,col)));
  set(h,'Color',colors(cidx),'FontSize',14,'FontWeight','bold');
end

4.- Other interesting commands:

imfill : fill holes. Specific locations can be fed.

imdilate : Dilating thin lines may also be useful

imclearborder : file rough edges