How to assign a name to ROI in MATLAB?.

I have a gray scale image. I want to draw multiple ROIs (impoly, imrect etc.) in the image and I have two things to do.

(1) I need to assign a particular name (Eg; ROI1, ROI2 etc.) to each ROI which is supposed to be displayed in image along with ROI.

(2) I also want to display the number of pixels in each ROI and this number should be updated whenever the position or dimension of ROI is changed.

I am stuck at this step and would really appreciate any suggestions. Thanks

[Walter Roberson]

Is it necessary to write the information into the image itself? For example are you using imwrite() to write the annotated images? Or is it enough that it is displayed on the screen?

[Sudhanshu Goel]

I atleast want to display the name of ROI (Eg: roi1, roi2) along with the ROI on the image. Rest of the information (No. of pixels etc.) need not be displayed in the image but it should get updated in the back end once the ROI position or dimension is changed.

Answer 1

[Walter Roberson]

text() the string into place if you only need to affect the display.

If you need to create a new image that has the text embedded in it then vision insertText

[Sudhanshu Goel]

Thanks Walter. I will try to implement this. Can you please tell me a way to get number of pixels in ROI when the position or dimension is changed. I am able to get this info when ROI is created but if I change the position or dimension of ROI this information is not updated.

[Walter Roberson]

impoly(), imrect(), imroi() create roi objects and return their handles. To get the number of pixels at the time of creation, you must be doing something with the handle. Just do that same thing any time you want to know the number of pixels.

You might want to use roi2mask() and then use nnz() on the mask, perhaps.

[Sudhanshu Goel]

I get you walter. Here is what I am doing to calculate number of pixels in the ROI (in this case number of pixels greater than 0.8). This works fine when the GUI is initially created. My question is how do I check if the position or dimension of ROI is changed so that I can repeat this operation.

h = imellipse();

BW = createMask(h);

BW = double(BW);

filter = Input_Image.*BW;

mask= filter>=0.8;

count=sum(mask(:));

[Walter Roberson]

roi objects do not contain any kind of "this object has changed" information, so what you could do is createMask again and compare to the previous mask.

[Walter Roberson]

Should have said poly2mask not roi2mask