ROI with hole, convert back to logical

Question

William Thielicke 2023-12-1

1
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2054769-roi-with-hole-convert-back-to-logical

编辑： William Thielicke 2023-12-7

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 2023-12-5

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 2023-12-7

编辑：William Thielicke 2023-12-7

@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