how can we calculate surface area for this leaf in matlab?

only the leaf

Answer 1

[Image Analyst]

Which leaf? There are lots of leaves in that image, and they're all green. That's the problem. So you can either hand trace the leaf with imfreehand(). Demo of imfreehand are attached below in blue.

Or you can try texture segmentation because the giant leaf has a different texture than the "background" leaves. You can use stdfilt or entropyfilt() to do texture segmentation.

Once you've processed it to a point where you can threshold it then you can use regionprops, as shown in my image segmentation tutorial: http://www.mathworks.com/matlabcentral/fileexchange/?term=authorid%3A31862 I also have color segmentation demos there but since all your leaves are so close in color, that probably won't work.

Finally, to get a "real world" area, instead of pixels, you'll need to spatially calibrate and I attach my demo (below in blue) to show you how to do that.

[nida]

what if its already threshold-ed then how do we compute surface area its not a leaf but still...

[Image Analyst]

For example

greenPixels = rgbImage(:,:,2) > 50; % Whatever works.
numGreenPixels = sum(greenPixels (:));

[Najwa Anwar]

What if I have this image and want to calculate the area of the leaves? I have the code that can forground the image, however, I got a blank image instead of only green. Can you help me

[Image Analyst]

You can use color segmentation by hue, or discriminant analysis (if you have the stats toolbox).

See my demo http://www.mathworks.com/matlabcentral/fileexchange/28512-simplecolordetectionbyhue-- or try the Color Threshlder app on the Apps tab of the tool ribbon.

[Image Analyst]

Did that work for you? If not, start your own question in a separate thread.

Answer 2

[Walter Roberson]

It looks to me that if you were to convert to brightness you could threshold on that to get most of the leaf. The heart of the leaf might not come out exactly right with that due to shadows.

Watershed segmentation would be another approach.