MATLAB: Outline polygon with square region

bounding regionboxpolygonregion

I have a polygon image(mask, 0's and 1's).

Let us pretend it is a octagon of width 200 pixels in a 500×500 pixel image. I want to draw a bounding box around the octagon, however, I want the bounding box to only be made up of 90 degree angles.

Another way to imagine the problem is, take a polygon and put it on a checkerboard. The sub-squares of the checkerboard that has the polygon in it gets a value of 1, and the squares that does not gets a value of 0.

Any ideas on how to easily do this?

Best Answer

left = find(any(TheMask,1), 1, 'first');
right = find(any(TheMask,1), 1, 'last');
top = find(any(TheMask,2), 1, 'first');
bottom = find(any(TheMask,2), 1, 'last');

These are going to be in pixels.

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mask = YourVoxels >= -100 & YourVoxels <= 200;
any1 = any(mask,1);
any12 = any(any1, 2);
start_pane = find( any12, 1, 'first');
end_pane = find( any12, 1, 'last');
any13 = any(any1, 3);
start_col = find( any13, 1, 'first');
end_col = find( any13, 1, 'last');
any23 = any(any( mask, 2), 3);
start_row = find( any23, 1, 'first');
end_row = find( any23, 1, 'last');
sub_volume = YourVoxels(start_row : end_row, start_col : end_col, start_pane : end_pane );

Alternately,

mask = YourVoxels >= -100 & YourVoxels <= 200;
rinfo = regionprops( double(mask), 'BoundingBox');
bb = rinfo.BoundingBox;
sub_volume = YourVoxels(bb(1) : bb(1) + bb(4) - 1, bb(2) : bb(2) + bb(5) - 1, bb(3) : bb(3) + bb(6) - 1);

Or if you want that more verbosely:

mask = YourVoxels >= -100 & YourVoxels <= 200;
rinfo = regionprops( double(mask), 'BoundingBox');
bb = rinfo.BoundingBox;
start_row = bb(1);
end_row = bb(1) + bb(4) - 1;
start_col = bb(2);
end_col = bb(2) + bb(5) - 1;
start_pane = bb(3);
end_pane = bb(3) + bb(6) - 1;
sub_volume = YourVoxels(start_row : end_row, start_col : end_col, start_pane : end_pane );

Best Answer

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