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Find Area, Perimeter, Centroid, Equivdiameter, Roundness and Bounding Box without Using MATLAB Function ‘regionprops’


In MATLAB, the function ‘regionprops’ is used to measure the image properties. Here are some basic properties computed without using the function.
          Read an image and find the connected components using ‘bwlabel’ function.
Using the Labeled matrix as an input, the properties can be measured.

Example:
A=[1 0 0 1
      1 1 1 1
      0 0 1 1]

To find Area:
·        The total number of ‘ON’ pixels in the image.

The number of ones in the matrix is 8.
              
To find Centroid:
·        Find the row and column having pixel value one. Eg.[row,column]=find(label==1)
Row=[ 1     2     2     2     3     1     2     3]
Column=[ 1     1     2     3     3     4     4     4]

·        Find the mean of the row and column having pixel value one.
Mean of Row=2 and mean of column= 2.75



To find the Bounding Box:
·        We need 4 points, starting position(x,y) , length and breadth.
·        Minimum value of row and column minus 0.5 gives starting position(x,y) respectively
·        Minimum value of  row=1-0.5=0.5
·        Minimum value of column=1-0.5=0.5
·        Maximum value of column – minimum value of column+1 gives breadth of the box
·        Maximum value of column=4
·        Max value-min value of column=3+1
·        Maximum value of row- minimum value of row +1gives length of the box
·        maximum value of row=3
·        Max value – Min value=2+1
·        Bounding Box value for the given example:0.5000    0.5000    4.0000    3.0000
·        For more details on how to draw a rectangle check here: http://angeljohnsy.blogspot.in/2011/06/how-to-draw-in-matlab.html



To find the Perimeter
·        Find the boundary of the labeled component
Boundary pixels:
     1     1
     2     2
     2     3
     1     4
     2     4
     3     4
     3     3
     2     2
     2     1
     1     1
·        Find the distance between the each adjoining pair of pixels around the border of the region.
·        Use the distance formula:
                                             
·        For instance, calculate the distance between the two points (1,1) and (2,2). distance=sqrt((2-1).^2+(2-1).^2)=1.41
·        Similarly, the distance is computed for all the pixel positions.
·        The perimeter for the given example is 10.2426

To find the Roundness:
·        Roundness of  an object can be determined using the formula: 
     Roundness=(4*Area*pi)/(Perimeter.^2) 
        If the Roundness is greater than 0.90 then, the object is circular in shape.
     Result= (4*8*3.14)/10.2426.^2=0.9582
           



To find the Equivdiameter
·        Formula: sqrt(4*Area/pi).
     Equivdiameter for the given example:3.1915
   

MATLAB CODE:

%Measure Basic Image Properties without using 'regionprops' function
%Measure Area, Perimeter, Centroid , Equvidiameter, Roundness and Bounding Box
clc
%Read Original Image
I=imread('coins.png');
%Convert to Binary
B=im2bw(I);
                                                 
%Fill the holes
C=imfill(B,'holes');
                                                    
 %Label the image
[Label,Total]=bwlabel(C,8);
%Object Number
num=4;
[row, col] = find(Label==num);

                                         
                                        
                                   
                               





%To find Bounding Box
sx=min(col)-0.5;
sy=min(row)-0.5;
breadth=max(col)-min(col)+1;
len=max(row)-min(row)+1;
BBox=[sx sy breadth len];
display(BBox);
figure,imshow(I);
hold on;
x=zeros([1 5]);
y=zeros([1 5]);
x(:)=BBox(1);
y(:)=BBox(2);
x(2:3)=BBox(1)+BBox(3);
y(3:4)=BBox(2)+BBox(4);
plot(x,y);

                              

%Find Area
Obj_area=numel(row);
display(Obj_area);
%Find Centroid
X=mean(col);
Y=mean(row);
Centroid=[X Y];
display(Centroid);
plot(X,Y,'ro','color','r');
hold off;
                                  

%Find Perimeter
BW=bwboundaries(Label==num);
c=cell2mat(BW(1));
Perimeter=0;
for i=1:size(c,1)-1
Perimeter=Perimeter+sqrt((c(i,1)-c(i+1,1)).^2+(c(i,2)-c(i+1,2)).^2);
end
display(Perimeter);
                                

%Find Equivdiameter
EquivD=sqrt(4*(Obj_area)/pi);
display(EquivD);


%Find Roundness
Roundness=(4*Obj_area*pi)/Perimeter.^2;
display(Roundness);
                          


%Calculation with 'regionprops'(For verification Purpose);
%Sdata=regionprops(Label,'all');
%Sdata(num).BoundingBox
%Sdata(num).Area
%Sdata(num).Centroid
%Sdata(num).Perimeter
%Sdata(num).EquivDiameter
                                           


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10 comments:

pka said... Reply to comment

how if we want find the properties for all coins in that image?

Aaron Angel said... Reply to comment

@pka

You can find it by using a for loop.
In the example,
%Label the image
[Label,Total]=bwlabel(C,8);
%Object Number
num=4;

'Total' represents the total number of coins.So you can use a for loop instead of specifying for a particular object.

abdullah said... Reply to comment

GREAT WORK

SUNIL KALE said... Reply to comment

sir how to find out compactness feature of the image

Mustaqeem Jan said... Reply to comment

how to find the center of rows and center of column in binary images using matlab

Mustaqeem Jan said... Reply to comment

how to find the parameter of binary images in matlab

Zaàfoury Rabàà said... Reply to comment
This comment has been removed by the author.
Zaàfoury Rabàà said... Reply to comment
This comment has been removed by the author.
Unknown said... Reply to comment

how to find centriod individually

Mansi nanda kumar said... Reply to comment

how to find the area of an irregular shape inside an image in matlab .....any particular code ?...please help

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