how to mask on roi area

hello sir/madam i want to mask some portion of image and that portion will decide by user not me. so how to mask the portion and how to get the detail about that mask portion like area.

Answer 1

[Image Analyst]

See my demos, attached.

[asthana]

thank you very much

Answer 2

[Dishant Arora]

you can ask user to interactively specify ROI:

I = imread('fullfilename');
imshow(I)
h = imfreehand(gca);
wait(h)  % waits for user to specify region of interest 
bw = createMask(h)  % Binary mask with 1's inside ROI

[asthana]

thank you mr.dishant arora