Image segmentation & confusion matrix

I've trained six(6) classes of features & performed image segmentation but trying to ascertain the accuracy of this, but it keeps telling me 'matrix dimension must agree' among the run error. Below is my segmentation code as well as roi.

he= imread('C:\Users\ISHOLA\Desktop\1.jpg'); imshow(he), title('ORIGINAL IMAGE'); text(size(he,2),size(he,1)+15,... 'Vellore,Tamilnadu,India', ... 'FontSize',7,'HorizontalAlignment','right'); cform = makecform('srgb2lab'); lab_he = applycform(he,cform); ab = double(lab_he(:,:,2:3)); nrows = size(ab,1); ncols = size(ab,2); disp(nrows); disp(ncols); ab = reshape(ab,nrows*ncols,2); nColors = 6; % repeat the clustering 3 times to avoid local minima [cluster_idx cluster_center] = kmeans(ab,nColors,'distance','sqEuclidean','replicates',6); pixel_labels = reshape(cluster_idx,nrows,ncols); %figure, imshow(pixel_labels,[]), title('image labeled by cluster index'); segmented_images = cell(1,3); rgb_label = repmat(pixel_labels,[1 3]);

for k = 1:nColors color = he; color(rgb_label ~= k) = 0; segmented_images{k} = color; end

ROI;

BW_1=roipoly(he);%for class 1

But on running this for the confusion matrix, it doesn't work [c,cm,ind,per] = confusion(BW_1,segmented_images{1});