How to write object connectivity code?

Question

tabw 2014-8-8

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/146872-how-to-write-object-connectivity-code

评论： Image Analyst 2014-8-10

 Actually I am writing a code for detecting a line and its size.But I encountered some problems.
 Can=im2bw(imread('Ims.png'));
  [X Y]= size(Can);
  result=[];
  region=[];
      for j= 1:Y;
         i=1; % initialize the while loop
            while i<299
              if (i~= 1) 
               if  (find(CellOutline(j,i)==0)) % check pixel itself is black
                 if (CellOutline(i-1,j) ==0)&& (CellOutline(i+1,j)==0) %check left pixel and right pixel of pixel(i) s black
                      region(i+1,j)=CellOutline(i+1,j); % write pixel(i+1,j) value into region
                 end
                   end
               elseif     (CellOutline(i,j)==0)&&(CellOutline(i+1,j)==0) %When i=1, check the forward point and point itself.
                         region(i,j)=CellOutline(i,j); %write the value into region.
                         region(i+1,j)=CellOutline(i+1,j); %\/
               else 
              end
              i=i+1;
              end
                end

I know lots of flaws in this code. Can this code even detect a continuous black line on binary image ?

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Answer 1

Image Analyst 2014-8-8

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/146872-how-to-write-object-connectivity-code#answer_147918

在 MATLAB Online 中打开

Not sure what that code does. To detect a black line in a gray scale image, do

blackLine = (grayImage == 0);

This actually detects all pure black pixels. You might have to filter it to find line-like region shapes. See my Image Segmentation Tutorial.

If that doesn't work for you then attach your Ims.png image so we can try your code or other code of our own.

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tabw 2014-8-9

在 MATLAB Online 中打开

## Copyright (C) 2000  Etienne Grossmann
##
## This program is free software; you can redistribute it and/or modify
## it under the terms of the GNU General Public License as published by
## the Free Software Foundation; either version 2 of the License, or
## (at your option) any later version.
##
## This program is distributed in the hope that it will be useful,
## but WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
## GNU General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with this program; if not, write to the Free Software
## Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
##       [im2,npix,bb] = bwlabel(im,...)
##
## Find the connected regions of an image.
##  
## im  : RxC 0-1 matrix
##
## im2 : RxC int matrix in which the connected regions of im have been
##       numbered. 4-neighborhoods are considered.
##
## npix : 1xQ int number of pixel in each region
##
## bb   : 4xQ int bounding boxes of the regions. Rows are minrow,
##        maxrow, mincol, maxcol.
##
## Since the algorithm is slow, it will report progress if it has to do
## more than 100 loops.
##
## Options :
##
## "verbose"  : Be verbose
## "quiet"    : Don't report anything (overrides "verbose")
## "prudent"  : Check that regions do not touch
## "mins", m  : Minimum size of the regions
## "maxs", m  : Maximum size of the regions
##
## Author:        Etienne Grossmann  <etienne@isr.ist.utl.pt>
## Last modified: January 2000
function [im2,npix,bb] = bwlabel(im,...)
[R,C]=size(im);
tr = 0 ;
        # Loop as little as possible
if R<C, tr = 1; im = im' ; [R,C]=size(im); end
report = C>100 ;
quiet = 0 ;
verbose = 0 ;
prudent = 1 ;
mins = maxs = 0 ;
filename = "bwlabel" ;
opt0 = " verbose quiet " ;
opt1 = " mins maxs " ;
nargin-- ;
read_options ;
if any(im(:)&im(:)!=1),
  printf("bwlabel : im is not binary\n");
  return
end
if quiet, verbose = report = 0 ; end
gsize = 100 ;      # Predicted number of slices
im2 = zeros(R,C);
## keyboard
        # find horizontal up/down going edges
imup =  max(im2, diff([zeros(1,C);im])) ;
imdo = -min(im2, diff([im;zeros(1,C)])) ;
im2 = ones(R,C);
######################################################################
## Find connected regions ############################################
rc = 1 ;      # Counter of region slices 
rnum = ones(1,gsize);    # List of labels of each slice
npix = zeros(1,gsize);    # Sizes of regions (actual size is in
        # region's first slice)
bb = zeros(4,gsize);    # Bounding boxes
if report && !verbose,
  printf("bwlabel : There will be %i loops ... \n%5i ",C,0) ;
end
lrow = zeros(R,1);    # Last treated image column
for i=1:C,
  ## i
  t1 = find(imup(:,i)) ;
  t2 = find(imdo(:,i)) ;
    nrow = zeros(R,1);    # Next row
    ## if i==42 || i==41,"i==42 || i==41", keyboard; end
    for j = 1:rows(t1(:)) ,  # Loop over slices of i'th column
      rc++ ;      # rc = number of current slice.
      im2(t1(j):t2(j),i) = rc ;
      ## if rc==341, "rc==341",keyboard; end
          # Slices from previous column that touch
          # this slice.
      rr = create_set(lrow(t1(j):t2(j))) ;
      if !isempty(rr) && !rr(1), rr = rr(2:length(rr)) ; end
      if rc>size(rnum,2),    # Get more space (uncertain effect on
          # speed; avoids resizing rnum and npix)
        tmp = 2*(ceil(C*rc/i)-rc+1+rows(t1(:))-j) ;
        sayif(verbose,"bwlabel : (i=%i) Foreseeing %i more regions\n",i,tmp);
        rnum = [ rnum, ones(1,tmp) ] ;
        npix = [ npix,zeros(1,tmp) ] ;
        bb = [ bb,zeros(4,tmp) ] ;
      end
      if isempty(rr),      # New region 
        sayif(verbose,"bwlabel : creating region %i\n",rc);
        r0 = rc ;      # r0 = number of the region
        bb(1,r0) = t1(j) ;
        bb(2,r0) = t2(j) ;
        bb(3:4,r0) = i ;
      else      # Add to already existing region #####
        ## rr
        r0 = rnum(rr(1)) ;
        bb(1,r0) = min(bb(1,r0),t1(j)) ;
        bb(2,r0) = max(bb(2,r0),t2(j)) ;
        bb(4,r0) = i ;
        # Touches region r0
      sayif(verbose,"bwlabel : adding to region %i\n",r0);
        # Touches other regions too
      for k = rr(find(rr!=r0)),  # Loop over other touching regions, that
        # should be merged to the first.
  sayif(verbose,"bwlabel : merging regions %i and %i\n",k,r0);
  rnum(find(rnum==k)) = r0 ;
  npix(r0) = npix(r0) + npix(k) ;
  bb([1,3],r0) = min(bb([1,3],r0)',bb([1,3],k)')' ;
  bb([2,4],r0) = max(bb([2,4],r0)',bb([2,4],k)')' ;
      end
      end        # End of add to already existing region
      ## if r0==259 && i==39,"r0==259",keyboard;end
      rnum(rc) = r0 ;
      npix(r0) = npix(r0) + 1+t2(j)-t1(j) ;
      nrow(t1(j):t2(j)) = r0 ;
    end        # End of looping over slices
    lrow = nrow ;
    if report && !verbose,
      printf(".") ;
      if !rem(i,70) && i<C, printf("\n%5i ",i); end
    end
  end        # End of looping over columns
  ## length(regs)
  if report && !verbose,
    printf("\n") ;
  end
  ## im2
  ## [ 1:rc ; rnum(1:rc) ]
  keep = ones(1,rc) ; 
if mins, keep = keep & (npix(rnum(1:rc))>=mins) ; end
if maxs, keep = keep & (npix(rnum(1:rc))<=maxs) ; end
keep(1) = 1 ;
keep = find(keep) ;    # Indices of slices to be kept
foo = create_set(rnum(keep)) ;  # Indices of regions to be kept
nr = prod(size(foo)) ;    # Number of regions (including bg)
## lrow = zeros(1,nr) ;
tmp = zeros(1,rc) ;
tmp(foo) = 0:nr-1 ;
bar = zeros(1,rc) ;
bar(keep) = tmp(rnum(keep)) ;
## keyboard
im2 = reshape(bar(im2),R,C) ;
npix = npix(foo(2:nr));
bb = bb(:,foo(2:nr));
if 0,        # Draw bb on the image (will ruin
        # coherence)
  for i=1:nr-1,
    im2([bb(1,i),bb(2,i)] ,bb(3,i):bb(4,i) ) = i ;
    im2( bb(1,i):bb(2,i) ,[bb(3,i),bb(4,i)]) = i ;
  end
end
## keyboard
if prudent,
    sayif(verbose,"bwlabel : Checking coherence\n");
    hcontact = im2 & im2!=[im2(:,2:C),zeros(R,1)] & [im2(:,2:C),zeros(R,1)] ;
    vcontact = im2 & im2!=[im2(2:R,:);zeros(1,C)] & [im2(2:R,:);zeros(1,C)] ;
    ok = 1 ;
    if any(hcontact(:)),
      ok = 0 ;
      printf("bwlabel: Whoa! Found horizontally connected separated regions\n");
    end
    if any(vcontact(:)),
      ok = 0 ;
      printf("bwlabel: Whoa! Found vertically connected separated regions\n");
    end
    if !ok, keyboard ; end
  end
## Eventually transpose result
if tr, 
  im2 = im2' ; 
  bb = bb([3,4,1,2],:);
end

Like this? What is the meaning of ##? same as %?

tabw 2014-8-10

编辑：tabw 2014-8-10

DO you understand the above code "gsize = 100 ; # Predicted number of slices" ? it is a 2D image. Where the slices come from? Or it partition 2D image to 100 regions by 100 slices?

Besides, the algorithm of connected object is so different from what I thought. I thought It is doing checking on every pixel and its neighbour.

BTW, I wanna ask Is there any method can calculate volume of every discrete object on stacks image? I just need how many pixels each object contains.