Measuring the size of regions in an image

Say that there are some regions I'm interested in in some image. How can I measure the size of such regions in MATLAB?

Thanks.

Answer 1

[Walter Roberson]

Use the Image Processing Toolbox with the regionprops() function.

Note: the result will be in square pixels. To convert the square pixels to a physical area, you will need information about the relationship between pixels and physical distance for that image.

[med-sweng]

Thanks for your answer. I used the property 'Area' in order to find the area of every labeled region. The question here is, for instance, say that I now have 300 labeled regions. I now know the area of each region. But, how can I know which region in the image each label represents. Say that I have a region with label "176". How can I know what part of the image represents this label?

[Image Analyst]

If you have also measured the centroids you can put a number over each blob. See my blobsdemo in my File Exchange for a demo of that.

Answer 2

[Image Analyst]

See my Image Segmentation Tutorial: http://www.mathworks.com/matlabcentral/fileexchange/?term=authorid%3A31862.

Also see attached spatial calibration demo, below in blue text.

[med-sweng]

Thanks for your reply. For the real world units used in the program, what are the units to be used? I for instance used "cm", but seems didn't work, or I may not be getting it correct.

[med-sweng]

I followed the steps, and entered the real world measure in "microns", but, getting the following:

Area= 0.0 square microns.

Mean gray level = NaN.

[Image Analyst]

You did not draw the area or length correctly. If you want, run psr.exe (from Windows) and record your screen movements so I can see what you did wrong.