How to get the Region of Interest using impoly?

How to use impoly function to get the ROI. From the following figure, How to show the ROI (i.e), the cut portion in the place of white portion in the second image?

Answer 1

[Image Analyst]

See my demo:

% Puts up an ellipse and masks and crops the image to the ellipse.
clc;  % Clear command window.
% clear;  % Delete all variables.
close all;  % Close all figure windows except those created by imtool.
imtool close all;  % Close all figure windows created by imtool.
workspace;  % Make sure the workspace panel is showing.
fontSize = 14;
% Change the current folder to the folder of this m-file.
% (The line of code below is from Brett Shoelson of The Mathworks.)
if(~isdeployed)
  cd(fileparts(which(mfilename)));
end

% Change the current folder to the folder of this m-file.
if(~isdeployed)
  cd(fileparts(which(mfilename)));
end
% Display images to prepare for the demo.
monochromeImage = imread('pout.tif');
subplot(2, 3, 1);
imshow(monochromeImage);
title('Original Image', 'FontSize', fontSize);
subplot(2, 3, 2);
imshow(monochromeImage);
title('Original Image with ellipse in overlay', 'FontSize', fontSize);
set(gcf, 'units','normalized','outerposition',[0 0 1 1]); % Maximize figure.
set(gcf,'name','Image Analysis Demo','numbertitle','off') 

%----- Burn ellipse into image -----
% Create elliptical mask, h, as an ROI object over the second image.
subplot(2, 3, 2);
hEllipse = imellipse(gca,[70 15 90 140]); % Second argument defines ellipse shape and position.
% Create a binary image ("mask") from the ROI object.
maskImage = hEllipse.createMask();
% Display the ellipse mask.
subplot(2, 3, 3);
imshow(maskImage);
title('Binary mask of the ellipse', 'FontSize', fontSize);
% Mask the image with the ellipse.
maskedImage = monochromeImage .* cast(maskImage, class(monochromeImage));
% Display the image with the "burned in" ellipse.
subplot(2, 3, 4);
imshow(maskedImage);
title('New image masked by the ellipse', 'FontSize', fontSize);
% Find the bounding box
column1 = find(sum(maskImage, 1), 1, 'first')
column2 = find(sum(maskImage, 1), 1, 'last')
row1 = find(sum(maskImage, 2), 1, 'first')
row2 = find(sum(maskImage, 2), 1, 'last')
croppedImage = maskedImage(row1:row2, column1:column2);
subplot(2, 3, 5);
imshow(croppedImage);
title('Ellipse portion cropped out', 'FontSize', fontSize);

[Sabarinathan Vadivelu]

Sir, Is there any possibility? without using imellipse or impoly commands can we crop the images in ellipse or polygonal format by specifying just the positions?

[Image Analyst]

Yes, if you knew all the pixel locations. But why do it the hard way?

[Sabarinathan Vadivelu]

Okay sir. Could you please tell me how extract the region of polygonal interest with using pixel locations?

[Image Analyst]

If x contains all the vertex x locations and y contains all the y locations

row1 = min(y);
row2 = max(y);
col1 = min(x);
col2 = max(x);
croppedRectangle = imageArray(row1:row2, col1:col2);

but this of course will be a rectangular bounding box because an image has to be rectangular. You can scan the original image over every pixel before this and use inpolygon() to set pixels outside the polygon to 0 so that those parts will look black in the cropped rectangular image.

[Karbala'a Unvi. Science]

Dear Image Analyst I liked your code and it worked for me ...but how to re pest that part back to the image after I do some process on that cropped area Thank you in advance

[Image Analyst]

Just reverse it:

imageArray(row1:row2, col1:col2) = croppedRectangle;

Answer 2

[Alex Taylor]

Look at the createMask method of impoly.

For example.

figure, imshow('pout.tif');
% Place polygon interactively.
hpoly = impoly(gca);
BW = createMask(hpoly);
figure, imshow(BW);

- Alex.