Blob analysis and thresholding

I have two white objects I detected by blob analysis the message should be "Alarm it is white !"

% Blob Analysis
BlobAnalysis = vision.BlobAnalysis('Connectivity',8);

[area,centroid,bbox] = step(BlobAnalysis,BW);

% Box
Ishape = insertShape(OriginalImage,'rectangle',bbox,'Linewidth',3);
subplot(2,2,2);
imshow(Ishape);

[row , col ] = size (bbox);
for i =1 : row
 x = bbox(i,1);
 y =bbox(i,2);
 w=bbox(i,3);
 h=bbox(i,4);
TestImage = OriginalImage(x:(x+w), y :(y+h),:);
r = TestImage(:,:,1);
g = TestImage(:,:,2);
b = TestImage(:,:,3);
subplot(2,2,3)
imshow(TestImage);

histogram2(r,g,'DisplayStyle','tile','ShowEmptyBins','on', ...
    'XBinLimits',[0 255],'YBinLimits',[0 255]);
histogram(r,'BinMethod','integers','FaceColor','r','EdgeAlpha',0,'FaceAlpha',1)
hold on
histogram(g,'BinMethod','integers','FaceColor','g','EdgeAlpha',0,'FaceAlpha',0.7)
histogram(b,'BinMethod','integers','FaceColor','b','EdgeAlpha',0,'FaceAlpha',0.7)
xlabel('RGB value')
ylabel('Frequency')
title('Color Histogram')
xlim([0 257])

threshold =128;
a = r.*g .*b;
c = 128.*128.*128;
if  a >= c
msgbox('Alarm it is white !');
else
    msgbox('ok');
end
clear TestImage;
end

I have a threshold which is equal to 128 if the color histogram for each object is greater than threshold the the message "Alarm .." is displayed !!

I think my mistake is here I don't know how can I do it:

threshold =128;
a = r.*g .*b;
c = 128.*128.*128;
if  a >= c
msgbox('Alarm it is white !');
else
    msgbox('ok');
end

Also I get some errors:

Index exceeds matrix dimensions.

Error in Tracking(line 25)
TestImage = OriginalImage(x:(x+w), y :(y+h),:);

THANK YOU !

Answer 1

[Image Analyst]

Make sure bbox is integers. Call round() if necessary. Often the bounding box is a half pixel outside of the pixel centers.

[Han]

bbox =

2×4 int32 matrix

   201    67   168   150
   436   293   147   119

[Image Analyst]

x is NOT the first index. It is row, which is y, not x. To correct:

TestImage = OriginalImage(y :(y+h), x:(x+w), :);