Question

I am working on a project thumb recognition. following is code I am reading the 118 images of order 42 X 25 and storing them in training matrix.

training=zeros(118, 1050);

imagefiles = dir('*.png');      
nfiles = length(imagefiles);    
for ii=1:nfiles
    currentfilename = imagefiles(ii).name;
    I = imread(currentfilename);

    BW=im2bw(I,graythresh(I));    

    temp = reshape(BW,1,1050);
    training(ii,:)=temp;
end

Now I am creating a matrix of labelData to assign labels to images.

labelData = zeros(118,1);
labelData(1:50,:) = 0; 
labelData(51:83,:) = 1;
labelData(84:118,:) = 2;

Here i am training my system by giving training data and label data.

options=optimset('MaxIter',5000);
SVMStruct =  svmtrain(training,labelData,'Kernel_Function','linear','QuadProg_Opts',options);

BUT when I run this code it is giving me an error like

Error 1 : SVMTRAIN only supports classification into two groups. GROUP contains 3 groups.
Error 2 : SVMStruct = svmtrain(training,labelData,'Kernel_Function','linear','QuadProg_Opts',options);

Kindly help me what is the problem I used it before it was working fine but now I dont know what is going on. Thanks in advance.

Answer 1

Error 1 tells you what the problem is – the MATLAB built-in SVM only supports binary classification. You are assigning 3 classes.

Your options are:

1. Construct three classifiers: 0 vs. 1,2 then 1 vs. 0,2 then 2 vs. 0,1 and look at the output of each.
2. Construct 0 vs. not 0 and then 1 vs. 2
3. Use a multi-class SVM trainer from LIBSVM or svmlight or other such packages.