Table Tennis Ball Detection-MATLAB CODE:

Using the concept of roundness to detect a circular object, the table tennis ball in mid air or in palm is detected.

FLOW CHART:

1.     Read input image

·        Read a RGB image with ball in mid air or ball in palm.

                   MATLAB CODE:

                       %Read the input image

         Img=imread(Filename);

         axes('Position',[0 .1 .74 .8],'xtick',[],'ytick',[]);

         imshow(Img);title('Original Image');

2.     Image Pre-processing

·        Convert the RGB image to grayscale image.

·        Apply median filter

·        Adjust the brightness and contrast of the image using ‘imadjust’ function.

                      MATLAB CODE:

           I=rgb2gray(Img);     % Converting RGB Image to

                                % Gray Scale Image

           I=im2double(I);      % Converting Gray scale Image

                                % to Double type

           J = medfilt2(I,[3 3]); % Median Filter , 

                                  % 3x3 Convolution

                                  % on Image

           I2 = imadjust(J);     % Improve to quality of Image

                                 % and adjusting

                                 % contrast and brightness values

3.     Threshold the image

·        The pixel value greater than the threshold value is converted to one else zero.

                     MATLAB CODE:

           Ib = I2> 0.9627; 

4.     Image Labeling

·        Label the connected components using ‘bwlabel’ function

·        Remove components that are smaller in size.

                     MATLAB CODE:

           %Labelling

           [Label,total] = bwlabel(Ib,4); % Indexing segments by

                                          % binary label function

            %Remove components that is small and tiny

            for i=1:total

                if(sum(sum(Label==i)) < 500 )

                    Label(Label==i)=0;

  

                end

            end

5.     Find the image properties: Area, Perimeter and Centroid

·        Using ‘regionprops’ function, find the Area, Perimeter, Bounding Box and Centroid.

                     MATLAB CODE:

            %Find the properties of the image

             Sdata = regionprops(Label,'all'); 

6.     Calculate the Roundness

·        Roundness = 4*PI*A/P^2

           MATLAB CODE:

                %Find the components number

          Un=unique(Label);

          my_max=0.0;

            %Check the Roundness metrics

            %Roundness=4*PI*Area/Perimeter.^2

            for i=2:numel(Un)

               Roundness=(4*pi*Sdata(Un(i)).Area)/Sdata(Un(i)).Perimeter.^2;

               my_max=max(my_max,Roundness);

                if(Roundness==my_max)

                   ele=Un(i);

                end

            end

7.     Find the component with the maximum roundness value

·        Find the max of the Roundness value for all the labeled components

8.     Show the detected table tennis ball

·        Use the ‘BoundingBox’ values to plot rectangle around the ball

·        Mark the centroid of the ball

                     MATLAB CODE:

          %Draw the box around the ball

           box=Sdata(ele).BoundingBox;

           box(1,1:2)=box(1,1:2)-15;

           box(1,3:4)=box(1,3)+25;

          %Crop the image

           C=imcrop(Img,box);

          %Find the centroid

          cen=Sdata(ele).Centroid;

          %Display the image

           axes('Position',[0 .1 .74 .8],'xtick',[],'ytick',[])

           imshow(Img);

           hold on

           plot(cen(1,1),cen(1,2),'rx');%Mark the centroid

9.     Generate report

·        Find the radius using the Equidiameter obtained using ‘regionprops’ function.

·        Display the radius,Area,Perimeter and Centroid of the ball.

·        Show the Binary and Original image of the cropped ball.

MATLAB CODE:

        Rad=(sdata(ele).EquivDiameter)/2;

        Rad=strcat('Radius of the Ball :',num2str(Rad));

     

        Area=sdata(ele).Area;

        Area=strcat('Area of the ball:',num2str(Area));

       

        Pmt=sdata(ele).Perimeter;

        Pmt=strcat('Perimeter of the ball:',num2str(Pmt));

       

        Cen=sdata(ele).Centroid;

        Cent=strcat('Centroid:',num2str(Cen(1,1)),',',num2str(Cen(1,2)));

BALL IN MID AIR: