How to create ROI object handle?

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Xingwang Yong
Xingwang Yong on 30 Sep 2022
Commented: Xingwang Yong on 5 Oct 2022
h = figure;
hg = findobj(h,'Type','hggroup')
% How can I "create" a ROI object so that I can call createMask()?
I'm trying to get ROI object handle, but it seems that it can not be retrieved after creation. Through property inspector, I found hggroup might be related to it. However, it is not the same as the handle returned by imrect().
Can I use hg to create a handle so that I can call createMask()?
The main problem is that I have to get the ROI object after its creation. In my application, the ROI creation is done in a callback, thus I can not get an output from it. So I need to find out information about ROI object from figure handle.

Answers (3)

Eric Delgado
Eric Delgado on 30 Sep 2022
% Directly draw your rectangle using your mouse:
roi = drawrectangle;
% Draw your rectangle programmatically:
% roi = images.roi.Rectangle(gca,'Position',[x,y,W,H]);
Xingwang Yong
Xingwang Yong on 3 Oct 2022
Thanks for your clarification. It seems it is not possible to go back to h given that I only have h.h_group. I hesitated to migrate to drawrectangle() because my application use old-style imrect() intensively. It might take me some time to do the migration.

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Image Analyst
Image Analyst on 3 Oct 2022
Try this:
h = figure;
uiwait(helpdlg('Drag out a box'))
rRect = imrect();
pos = rRect.getPosition
mask = rRect.createMask;
Xingwang Yong
Xingwang Yong on 5 Oct 2022
Yes, Simon's method would fail when facing sophiscated ROIs, e.g. freehand. If I can not gather enough info from figure handle, saving a variable is the only way that works.

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Simon Chan
Simon Chan on 3 Oct 2022
You may try the following:
h = figure;
imrect(); % not use the output of imrect()
hAx=findobj(ax.Children,'-regexp','Tag','corner marker');
x = cat(1,hAx.XData);
y = cat(1,hAx.YData);
roi = [min(x) min(y), max(x)-min(x) max(y)-min(y)]
Xingwang Yong
Xingwang Yong on 3 Oct 2022
Yes. Although this is a little bit tedious, at least it works. Thank you Simon.

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