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getExactBounds (get exact boundary)

version 2.0 (5.75 KB) by Jiexian Ma
Obtain the exact polygonal boundaries of objects and holes in a binary image.


Updated 23 May 2020

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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.

If you have any questions or suggestions, feel free to send me an email., May 2020.

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.

Cite As

Jiexian Ma (2020). getExactBounds (get exact boundary) (, MATLAB Central File Exchange. Retrieved .

Comments and Ratings (0)



rewrite the whole function



MATLAB Release Compatibility
Created with R2018a
Compatible with any release
Platform Compatibility
Windows macOS Linux