Displaying area of each labeled region

I would like to display area for each labeled region in the generated result image, after binarize and labeling gray-scale image. This is part of the codes:

hold on;
Measurements = regionprops(labImg, fgImg, 'all');   
numberOfBlobs = size(Measurements, 1);
for k = 1:numberOfBlobs 
  areas=Measurements(k).Area;
  plot(areas(:,2), areas(:,1), 2);
end
hold off;

Besides that, is there any idea to display labeled no. and area of labeled image in orders in command window?

Answer 1

[Walter Roberson]

You should be able to use this outside of a loop:

blobareas = [Measurements.Area];
printf('%3d: %5d\n', [1 : length(blobareas); blobareas]);

Note: the Area field returned by regionprops() will always be a scalar, so accessing the second column of it like you do in areas(:,2) will cause an error.

[Syahrul Niezam]

Does it suppose to be like this?

Measurements = regionprops(labImg, fgImg, 'area');

numberOfBlobs = size(Measurements, 1);

blobareas = [Measurements.Area];

hold on;

printf('%3d: %5d\n', [1 : length(blobareas); blobareas]);

for k = 1:numberOfBlobs

plot(areas(:,1));

end

hold off;

[Walter Roberson]

The regionprops has to be done before the code I showed, but the other code you added is not relevant to the task of "displaying the labeled no. and area of labeled image in orders in command window".

If you must plot then:

Measurements = regionprops(labImg, fgImg, 'area');

blobareas = [Measurements.Area];

printf('%3d: %5d\n', [1 : length(blobareas); blobareas]);

plot(blobareas);

with no loop and no "areas" array needed.

[Syahrul Niezam]

These are the codes:

subplot(223);imshow(labImg, []);

hold on;

Measurements = regionprops(labImg, fgImg, 'area');

blobareas = [Measurements.Area];

printf('%3d: %5d\n', [1 : length(blobareas); blobareas]);

plot(blobareas);

hold off;

However, there is error came out in printf line.

[Walter Roberson]

Sorry should be fprintf rather than printf

Are you expecting the area of each blob to be shown on the image near the blob? Or are you expecting that the graph of the areas will show up on top of the image, drawn to what-ever scale and position that plot() finds convenient?

[Syahrul Niezam]

Thank you very much for your help.

Actually I'm confused; either to display the area in generated image, or displaying in command window. But, it is better the values are represented in variables, so that can be applied for the next command etc.

[Walter Roberson]

If you only need the area shown on the screen, go back to the code in my Answer (except switching to fprintf and adding the Measurements assignment.)

Please explain further about how you would like to see the values represented as variables? With the code I posted earlier, the K'th blob's area is in blobarea(K)

[Image Analyst]

He wanted to display the area "in the generated result image" so in that case he needs to get the centroid (via regionprops) and create a string with sprintf() and call text() to display it in the image at the location of the centroid, like I do in BlobsDemo. (I think I told him this already in one of his other related questions.)

Answer 2

[Image Analyst]

That looks strange. Why is areas a 2 element array, or a N by 2 array??? Anyway....

See my BlobsDemo http://www.mathworks.com/matlabcentral/fileexchange/25157 where I plot the label number at the centroid of the object. Basically you get the centroid and any other measurements you want then use sprintf() to create a string, then display that string with text() at the location of the centroid.

[Syahrul Niezam]

Oh, i just copied the blob demos;

plot(thisBoundary(:,2), thisBoundary(:,1),.....

[Image Analyst]

Yeah, boundaries is an N by 2 array of elements going around the boundary of a blob representing the x and y coordinates for each vertex. The area is just a single number. You can't plot one column of area against the other because there are not two columns of areas, just one.

[Syahrul Niezam]

Thanks! I got it/ :)

[MMSAAH]

Hello Image Analyst,

I read your demo.

Please, tell me if is it possible to numerate coins from top to bottom ?

Thanks in advance.

[Image Analyst]

Yes, you can reorder the blobMeasurements (I think that's the name) that I got from regionprops():

blobMeasurements = props(binaryImage, 'Centroid', 'Area', 'EquivDiameter');
% Get all centroids
allCentroids = vertcat(props.Centroid);
% Sort according to centroid's vertical location.
[sorted_y, sortOrder] = sort(allCentroids(:, 2), 'ascend');
% Reorder blobMeasurements
blobMeasurements = blobMeasurements(sortOrder);

Now blob #1 is the top-most, and the last one is the bottom-most one.

[MMSAAH]

Thank you for your reply and for sharing.

I ve changed the proposed code by :

blobMeasurements = regionprops(binaryImage, 'Centroid', 'Area', 'EquivDiameter');
% Get all centroids
allCentroids = vertcat(blobMeasurements.Centroid);
% Sort according to centroid's vertical location.
[sorted_y, sortOrder] = sort(allCentroids(:, 2), 'ascend');
% Reorder blobMeasurements
blobMeasurements = blobMeasurements(sortOrder);

Now it works.

[Image Analyst]

OK. Sorry about that. Lately I've just been using props instead of blobMeasurements because it's shorter to type.