getExactBounds (get exact boundary)

Obtain the exact polygonal boundaries of objects and holes in a binary image.

getExactBounds returns the coordinates of corners on image boundaries, while Matlab function bwboundaries() is only able to obtain the coordinates of boundary pixel locations.

getExactBounds is used by my other program - im2mesh (2D image to triangular meshes).

You can start with demo.m in the folder.

Note:

There're huge differences between function bwboundaries and getExactBounds.

The output of bwboundaries and getExactBounds may have different lengths.

1. bwboundaries(BW,connectivity,options)

Return row (y) and column (x) coordinates of boundary pixel locations.

Only inner boundaries are obtained.

Parameter connectivity is very important for function bwboundaries.

According to bwboundaries.m in Matlab,

if connectivity = 4, objects are 4 connected and holes are 8 connected;

if connectivity = 8, objects are 8 connected and holes are 4 connected.

This is to avoid topological errors.

2. getExactBounds( bw )

Return column (x) and row (y) coordinates of the corners on boundaries of objects and holes.

However, function getExactBounds don't have the connectivity parameter.

Both objects and holes are 4 connected, since outputs are exact boundary.