For multichannel images, MorphologicalGraph operates on the intensity averaged over all channels.
The morphological branch points and endpoints of the image skeleton are converted into vertices. The graph exhibits an undirected edge between two vertices if the corresponding branch points or endpoints are 8-connected by the skeleton.
For EdgeWeight->Automatic the weight of each edge is set to the number of pixels in the corresponding skeleton connection. If more than one connection exists, the shortest one is chosen to represent the weight of the edge.