Lines surrounding contiguous regions in an image can be extracted using MATLAB's built-in contour/contourc functions, but these functions perform linear interpolation between pixels leading to 'cut corners'. bwperim from the imaging toolbox will trace boundaries without interpolation, but only provides its result as a pixel map. This function, bwperimtrace, instead outputs line segments that entirely contain all non-zero pixels in the input image. The package also includes contourc4, a replacement for contourc, which doesn't perform any interpolation between pixels.
Daniel Warren (2020). Trace perimeter of binary image with line segments (bwperimtrace) (https://www.mathworks.com/matlabcentral/fileexchange/49551-trace-perimeter-of-binary-image-with-line-segments-bwperimtrace), MATLAB Central File Exchange. Retrieved .
Bug in bwperimtrace.m. It fail to get 4-connected neighbourhood in the following case.
>> im=[ 1 0 0; 1 0 1; 1 1 0];
>> b= bwperimtrace( im == 1 );
Small bug in bwperimtrace.m, Lines 27 ( in = in'; ) should be moved to line 14. In the code, x is column direction, y is row direction.
Powerful function! Work for me!
Small bug, on lines 32 and 33, change to:
xpix = xlims(1):dx:xlims(end);
ypix = ylims(1):dy:ylims(end);
Inspired: Im2mesh (2D image to triangular meshes)
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