get the actual position correspond to imfreehand

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chess
chess on 17 Aug 2014
Edited: chess on 22 Aug 2014
Hi I have a question. I have a grayscale image, I chose a region using imfreehand command and I have its position. I can convert to the mask but that is a binary image how can I extract the exact image that is correspond to region of imfreehand from the grayscale image. Meaning that imcrop returns the cropped version of grayscale image I want to do the same thing here.
imshow(image1)
h=imfreehand;
pos=getPosition(h)
Then I like to have something like image(pos) to extract the portion from grayscale image. However this is of course is a error because the subscript is a fraction.

Accepted Answer

Ben11
Ben11 on 17 Aug 2014
After you get the position, you can create a mask in which value inside the ROi are equal to 1 and those outside are equal to 0. Then you assign those 0-values to the original image. Please try the following code and see what happens, is this what you want to achieve?
clear
clc
A = rgb2gray(imread('peppers.png'));
figure;
hold on
subplot(1,2,1)
imshow(A)
hRoi = imfreehand(gca);
Position = getPosition(hRoi);
BW = createMask(hRoi);
A(BW == 0) = 0;
subplot(1,2,2)
imshow(A)
hold off
  2 Comments
Ben11
Ben11 on 17 Aug 2014
I think the best you can do is crop a rectangular image with the boundaries of the ROI touching the sides, is it what you mean? If so you can you imcrop with the coordinates of the enclosing black rectangle? For example, "Position" in my example above outputs a 2-column array, in which the first corresponds to the x and the 2nd corresponds to the y-coordinates. You can fetch the maximum and minimum for each coordinate:
xmin = min(Position(:,1))
xmax = max(Position(:,1))
ymin = min(Position(:,2))
ymax = max(Position(:,2))
and then use imcrop as usual.

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