How to create ROI object handle?

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Xingwang Yong
Xingwang Yong 2022-9-30
评论： Xingwang Yong 2022-10-5
h = figure;
imshow(imread('pout.tif'));
imrect();
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()?
Edit:
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.

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回答（3 个）

Eric Delgado
Eric Delgado 2022-9-30
Replace imrect for images.roi.Rectangle. See the first example of the doc - https://www.mathworks.com/help/images/ref/images.roi.rectangle.html
figure;
imshow(imread('pout.tif'));
% Directly draw your rectangle using your mouse:
roi = drawrectangle;
% Draw your rectangle programmatically:
% roi = images.roi.Rectangle(gca,'Position',[x,y,W,H]);
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Eric Delgado
Eric Delgado 2022-10-3
The handle for a uirect() has just one public property ("Deletable"). If you use struct to see its implementation, you will get a few more...
fig = figure;
ax1 = axes(fig);
imshow(imread('pout.tif'));
h = imrect()
% h =
% imrect with properties:
% Deletable: 1
h = struct(h)
% h =
% struct with fields:
% api: [1×1 struct]
% h_group: [1×1 Group]
% draw_api: [1×1 struct]
% graphicsDeletedListener: [1×1 event.listener]
% Deletable: 1
% hDeleteContextItem: [1×1 Menu]
isequal(findobj('Type', 'hggroup'), h.h_group)
% ans =
% logical
% 1
Xingwang Yong
Xingwang Yong 2022-10-3
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 2022-10-3
Try this:
h = figure;
imshow(imread('pout.tif'));
uiwait(helpdlg('Drag out a box'))
rRect = imrect();
pos = rRect.getPosition
mask = rRect.createMask;
figure;
imshow(mask)
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Image Analyst
Image Analyst 2022-10-4
Well then you'll need to save them. What Simon showed you only works as long as the graphical roi object is still there in the axes. If you ever cleared the axes, like by displaying a different image, then it will be gone and there's no way to get it back. So if you ever plan on displaying an image, drawing an roi, and then displaying another image, you'll have to have the roi saved into a variable, rather than an object in the axes container. I don't recommend Simon's solution in the more general case of using one or more ROIs on one or more images, which is what it sounds like what you want to do.
Xingwang Yong
Xingwang Yong 2022-10-5
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 2022-10-3
You may try the following:
h = figure;
imshow(imread('pout.tif'));
imrect(); % not use the output of imrect()
ax=gca;
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)]
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Simon Chan
Simon Chan 2022-10-3
You may need to tackle them differently:
h = figure;
imshow(imread('pout.tif'));
drawpolygon
ax = gca;
hAx = findobj(ax.Children,'-property','Position');
hAx.Position % Gives you the vertices for drawpolygon
Xingwang Yong
Xingwang Yong 2022-10-3
Yes. Although this is a little bit tedious, at least it works. Thank you Simon.

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