The definition of 8-adjacency and m-adjacency are clear. But is there a case where two pixels p and q can be 8-adjacent, but not m-adjacent. I have given the definition of 8-adjacent and m-adjacent below:
8-adjacency: two pixels p and q with values from V are 8-adjacent if q is in the set N8(p).
m-adjacency: two pixels p and q with values from V are m-adjacent if
i) q is in N4(p), OR
ii) q is in ND(p) AND the set N4(p) N4(q) has no pixels whose values are from V.