mmskelm
Morphological skeleton (Medial Axis Transform).

a=mmneg(mmframe(mmbinary(ones((7,9)))))

Warning: downcasting image from double to int32 (may lose precision)

print a

[[False False False False False False False False False]
 [False  True  True  True  True  True  True  True False]
 [False  True  True  True  True  True  True  True False]
 [False  True  True  True  True  True  True  True False]
 [False  True  True  True  True  True  True  True False]
 [False  True  True  True  True  True  True  True False]
 [False False False False False False False False False]]

print mmskelm(a)

[[False False False False False False False False False]
 [False  True False False False False False  True False]
 [False False  True False False False  True False False]
 [False False False  True  True  True False False False]
 [False False  True False False False  True False False]
 [False  True False False False False False  True False]
 [False False False False False False False False False]]

print mmskelm(a,mmsebox())

[[False False False False False False False False False]
 [False False False False False False False False False]
 [False False False False False False False False False]
 [False False False  True  True  True False False False]
 [False False False False False False False False False]
 [False False False False False False False False False]
 [False False False False False False False False False]]

a=mmreadgray('pcbholes.tif')

b=mmskelm(a)

mmshow(a)

mmshow(b)

c=mmskelm(a,mmsecross(),'value')

mmshow(c)