regionprops( aImage, 'Centroid', 'Image' ) vs regionprops( aImage, 'Centroid' );

I am new to MatLab.

I am working with code harvested from the internet that lacks comments.

In one place there is a call:

x = regionprops(  aImage, 'Centroid', 'Image' );

and in another place is a call

x = regionprops(  aImage, 'Centroid' );

using the same image.

The Help for regionprops is extensive, but I cannot figure outwhat the difference would be between those two calls.

Can somebody fill me in? Is this something that needs to be documented?

Answer 1

[Walter Roberson]

Each option to regionprops() tells it another property to measure and return

https://www.mathworks.com/help/images/ref/regionprops.html#buoixjn-1-properties

• Centroid: Center of mass of the region, returned as a 1-by-Q vector. The first element of Centroid is the horizontal coordinate (or x-coordinate) of the center of mass. The second element is the vertical coordinate (or y-coordinate). All other elements of Centroid are in order of dimension.
• Image: Image the same size as the bounding box of the region, returned as a binary (logical) array. The on pixels correspond to the region, and all other pixels are off.

Thus the first of the calls returns a struct into x that has fields Centroid and Image with values as described above, and the second of the calls returns a struct into x that has only field Centroid with value as described above.

The 'Image' option does not change the way that the centroid is computed: it says to also compute something more and return it.

[Richard Hall]

Wonderful answer.

If only "help regionprops" was as informative in such a clear manner.

Thank you.