Save ROI Object and load it later again

I have several pictures where the User defines different ROI-Objects. The user can switch between the currently displayed picture (Only one image is displayed at a time). Now I want to store each ROI-Object corresponding to each picture and load them when the User comes back to the picture with the corresponding ROI-Object. To be clear: The (re)loaded ROI-Object needs to be still customizable.

I saved each handle to the corresponding ROI-Object but now I don't have a clue how to show the ROI-Object again. How can I do this?

[Adam]

What is an 'ROI-object'? An imroi or something else?

[Image Analyst]

@Adam, drawpolygon() returns a variable that they call roi but is actually a variable of the "polygon" class.

The old imroi class from the Image Processing Toolbox is not recommended anymore, according to the help.

Answer 1

[Image Analyst]

Simply use save() to save your variable into a .mat file

save('roi.mat', 'yourROIVariable');

To recall:

s = load('roi.mat');
yourROIVariable = s.yourROIVariable;

[hedgehog]

Possibly this is not what SturmGhost meant. I have the same problem and like to use drawpolygon() to select an area in a plot. The desired shape is somewhat intricate. It would be nice to be able to apply modifications later. So there is need for a function to draw a polygon (or some other roi) on an image or plot with the option to start with an existing one. This could be saved and loaded as shown above.

[Image Analyst]

@hedgehog each time you call

thisROI = drawpolygon();

it will return an ROI object. You can save it, or an array of them, in a .mat file like I showed. You can then recall all of them from the mat file later and use them again.

It doesn't matter whether you start with none, one or more in your existing program session, or with one or more that you recalled from a .mat file. Bottom line is each time you call drawpolygon you will get a new ROI object. You can collect a whole bunch of them if you want.

I'm not sure you can pass an existing object into drawpolygon() and modify it. If you can, I'm not seeing that in the help. I'd just delete it (any you don't want) and ask the user to draw it again.

If you want the outlines of lots of polygons you drew, you can get the position properties of each of them and create a binary image (mask) with that polygon. Then OR all the masks together to get a mask of the entire group. You can get boundaries of the regions with bwboundaries().

[hedgehog]

Thanks Image Analyst,

that is what I had assumed. Yet it does not please me much. Indeed it is possibly to modify a polygon with drawpolygon(). However the new vertices are just visible in the figure. Can they be accessed somehow?

% display the standard deviation

S = std(sobotpresData,1,3);

imagesc(S)

caxis([0 500])

title('standard deviation / Pa')

colorbar

% load existing polygon

load('h.mat')

vertices=h.Position;

% draw the existing polygon - it can be modified and extended but - how can the

% new polygon data be used?

ho = drawpolygon('Position',vertices,'Color','r');

save('h.mat','ho')

h =

Polygon with properties:

Position: [3×2 double]

Label: ''

Show all properties

>> ho

ho =

Polygon with properties:

Position: [3×2 double]

Label: ''

Color: [1 0 0]

Parent: [1×1 Axes]

Visible: on

Selected: 0

even though 2 more vertices were added

Looks like I have to:

-take a consumer attitude and try to like what is offered

or

- write an alternative to drawpolygon() by myself.

[Image Analyst]

I'm not sure what the code you posted is supposed to demonstrate. Anyway, it does not run.

[Nat]

@Image Analyst

When I try to save my ROI from drawellipse, it says it must be a text scalar. Here is my code. Do you know what to do?

Code:

file2Open = fullfile('LabeltheSkeleton.png');

image1 = imread('LabeltheSkeleton.png');

leftClavicleROI = drawellipse('Position', [100, 300]);

save('leftClavicleROI.mat', leftClavicleROI);

variable1 = load('leftClavicleROI.mat');

Error Message:

Error using save

Must be a text scalar.

Error in TestingFinalProjectParts (line 14)

save('leftClavicleROI.mat', leftClavicleROI);

[DGM]

You need to pass the name of the variable, not the variable itself.

save('leftClavicleROI.mat', 'leftClavicleROI');