Usage of regionprops3 command

How does the command 'regionprop3' interpret an RGB image? The reference page for the same tabulates some properties for grayscale images but it is accepting RGB and HSV (three channel) images.

And how to interpret or calculate 'orientation' and 'ConvexVolume' properties?

If regionprops3 cannot be used for 3 channel images, is there a way to get the lengths of major and minor axes of a convex hull produced by 'convhull' command?

Answer 1

[Guillaume]

but it is accepting RGB and HSV (three channel) images.

No, regionprops3 is for volumes exclusively. If you pass it a 2D colour image (MxNx3) it will be interpreted as a (very thin, only 3 layers) 3D label matrix.Or if you're talking about colour volumes (MxNx3xP), these can't be passed to regionprops3 directly, you'll need to convert to greyscale and then binarise the volume.

If you are working with 2D images, you need to use regionprops not regionprops3. Again, a colour image must be binarised (or labeled).

[Pooja Patil]

How do I measure the Principal Axis Length of the below figure? I request to kindly help