# ROI with hole, convert back to logical

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William Thielicke 2023 年 12 月 1 日

Hi,
I have a task that has probably been asked before, but I do not find something about this issue.
I have a binary mask that is converted to a ROI, then edited, then converted back to a binary mask. The binary mask contains objects with holes in it. The ROI contains objects for the holes, but when converting back to binary, these holes are lost. I am looking for a simple soution for this (code is mainly from Matlab help):
A=zeros(1000,1000,'logical');
A(200:800,200:800)=1;
A(300:400,300:400)=0;
blocations = bwboundaries(A,'holes');
figure
imshow(A, []);
for ind = 1:numel(blocations)
% Convert to x,y order.
pos = blocations{ind};
pos = fliplr(pos);
% Create a freehand ROI.
drawfreehand('Position', pos);
end
% Convert edited ROI back to masks.
hfhs = findobj(gca, 'Type', 'images.roi.Freehand');
editedMask = false(size(A));
for ind = 1:numel(hfhs)
% Accumulate the mask from each ROI
editedMask = editedMask | hfhs(ind).createMask();
% Include the boundary of the ROI in the final mask.
% Ref: https://blogs.mathworks.com/steve/2014/03/27/comparing-the-geometries-of-bwboundaries-and-poly2mask/
% Here, we have a dense boundary, so we can take the slightly more
% performant approach of just including the boundary pixels directly in
% the mask.
boundaryLocation = hfhs(ind).Position;
bInds = sub2ind(size(A), boundaryLocation(:,2), boundaryLocation(:,1));
editedMask(bInds) = true;
end
The aim is that "editedMask" looks like "A" after these two conversions. Thanks for your help!!
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DGM 2023 年 12 月 5 日
Will that be okay if you have two "holes" overlap or something? Should that create one large hole with an unattached island, or should it just be one large hole? I mean, these are design decisions for you, but I think your method is one possible solution.
William Thielicke 2023 年 12 月 7 日

@Image Analyst: These "masks" are meant to be used in a GUI to exclude certain regions of images from analysis. These masks can be generated by the user in different ways: Drawing by hand, or importing a user-generated binary image. In both cases, I want to keep the masks editable until they are used in the final image analysis. I also want to offer some basic image processing on the imported binary mask: imdilate, imerode, imclose etc. Therefore, I think the best way is to work with Matlabs ROI objects all the time, and convert them back to binary at the very end (because a binary mask is what the final analysis expects).
I am trying to find a good solution that really helps people to define masks, but as @DGM noticed, I have to take a lot of design decisions which feels pretty difficult at the moment.
Currently, the even/uneven method seems to be compatible with imported binary masks and with masks that are drawn with polygons. I personally think the behaviour makes sense, but it is difficult to assess how others feel about it.
Polygon mask behaviour:
User input
Conversion to pixels result:
Pixel mask behaviour:
User input (binary pixel image):
Conversion from pixel mask to polygon mask (editable):
Conversion back to pixels result:

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