save coordinates by using impoly..

Hi, I am using imrect to select what I need from image and save the coordinates and then show the image with that coordinates see the code

I = imread('gantrycrane.png');
imshow(I);
s = imrect;
P = getPosition(s)
x=P(1,1);
y=P(1,2);
w=P(1,3);
h=P(1,4);
II = I(y:y+h,x:x+w);
imshow(II);

now I want to use impoly to do same thing like what I did with imrect I want to select what I need by using impoly and save the coordinates and show the image with that coordinates ... I wish my question is clear ...

Answer 1

[Image Analyst]

Try this:

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 20;

sourceImage = imread('peppers.png');
subplot(2, 2, 1);
imshow(sourceImage);
title('Original Image', 'FontSize', 20);

% Set up figure properties:
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);
% Get rid of tool bar and pulldown menus that are along top of figure.
set(gcf, 'Toolbar', 'none', 'Menu', 'none');
% Give a name to the title bar.
set(gcf, 'Name', 'Demo by ImageAnalyst', 'NumberTitle', 'Off') 
uiwait(msgbox('Draw a polygon.  Double click to accept/finish it'));
hPoly = impoly;
polyPoints = hPoly.getPosition
mask = hPoly.createMask;
subplot(2, 2, 2);
imshow(mask);
title('Mask', 'FontSize', 20);

croppedImage = sourceImage; % Initialize
% Set outside of polygon to black
croppedImage(~repmat(mask, 1, 1, 3)) = 0; 

x1 = round(min(polyPoints(:, 1)))
x2 = round(max(polyPoints(:, 1)))
y1 = round(min(polyPoints(:, 2)))
y2 = round(max(polyPoints(:, 2)))

% Do a rectangular crop
croppedImage = croppedImage(y1:y2, x1:x2, :);
subplot(2, 2, 3);
imshow(croppedImage);
title('Cropped Image', 'FontSize', 20);

[Khaled Al-Faleh]

Thanks sir :).

[Image Analyst]

You're welcome. Actually to make sure you capture the complete image, don't use round() - use ceil() and floor() instead:

x1 = floor(min(polyPoints(:, 1)))
x2 = ceil(max(polyPoints(:, 1)))
y1 = floor(min(polyPoints(:, 2)))
y2 = ceil(max(polyPoints(:, 2)))

[Khaled Al-Faleh]

Ok sir :)

[Khaled Al-Faleh]

Sir I want to put a red rectangular box to what we cut I used this but not working will

rectangle('Position',[x1 y1 x2 y2],'EdgeColor','r','LineWidth',2);

[Image Analyst]

The Position property takes [xLeftColumn, yTopLine, xWidth, yHeight], not [x1 y1 x2 y2].

[Khaled Al-Faleh]

Ok sir but in our code before how I get [xLeftColumn, yTopLine, xWidth, yHeight]

rectangle('Position',[x1 y1 x2 y2],'EdgeColor','r','LineWidth',2);

[Image Analyst]

Well, isn't the width equal to x2-x1? And the height y2-y1??????

So, did you try

rectangle('Position',[x1, y1, abs(x2-x1), abs(y2-y1)],'EdgeColor','r','LineWidth',2);

[Guillaume]

@Khaled,

reading all your questions in this thread, it's clear that you haven't spend the time to understand what the code does in any of our answers. Everything you need was given in my original answer and if you'd try to understand what it did (that is what (min(polypoints(:, 2)) and co. represent), you would have had no need to ask any of the subsequent questions.

It's incredibly frustrating to answerers, when the person asking the question do not try to understand the answer they're given.

[Khaled Al-Faleh]

Ok million of thanks to u all and sorry I will not ask again any more :)

Answer 2

[Guillaume]

Well, you can't crop an image to an arbitrary polygon since an image must be rectangular. Guessing, maybe you want the image crop to the bounding box of the polygon, with all pixels outside the polygon set to black:

sourceimage = imread('gantrycrane.png');
imshow(sourceimage);
hpoly = impoly;
polypoints = hpoly.getPosition;
croppedimage = sourceimage;
croppedimage(~repmat(hpoly.createMask, 1, 1, 3)) = 0; %set outside of polygon to black
croppedimage = croppedimage(min(polypoints(:, 2)):max(polypoints(:, 2)), min(polypoints(:, 1)):max(polypoints(:, 1)), :);
imshow(croppedimage)

[Khaled Al-Faleh]

so sir there is no way to do what I want ??

[Guillaume]

Well, considering you haven't told us what it is you want in enough detail, I'd say my answer does what you want.

If not, please explain what it is you want exactly. Preferably by showing examples.

[Khaled Al-Faleh]

Ok sir thanks for what u did but one more question please in your code the last croppedimage how I can get its coordinates the x,y,w and h of it ?

[Guillaume]

What do you think

min(polypoints(:, 2)):max(polypoints(:, 2))
min(polypoints(:, 1)):max(polypoints(:, 1))

is in the line that performs the crop, if not the bounds of the cropped image?

[Khaled Al-Faleh]

sir see the image its about parking and I select a spot by impoly then I want to save its coordinates then use it to show it by original image because I will select many spots. I see the code sir I wish its clear.

sourceimage = imread('A.png');
imshow(sourceimage);
hpoly = impoly;
polypoints = hpoly.getPosition;
croppedimage = sourceimage;
croppedimage(~repmat(hpoly.createMask, 1, 1, 3)) = 0; %set outside of polygon to black
croppedimage = croppedimage(min(polypoints(:, 2)):max(polypoints(:, 2)), min(polypoints(:, 1)):max(polypoints(:, 1)), :);
imshow(croppedimage)

x = min(polypoints(:, 2))
w = max(polypoints(:, 2))
y = min(polypoints(:, 1))
h = max(polypoints(:, 1))

II = sourceimage(x:x+h,y:y+w);
figure,imshow(II);

[Khaled Al-Faleh]

II = sourceimage(x:x+h,y:y+w);
figure,imshow(II);

here the problem does not show the same that I select..

[Image Analyst]

Why do you think images are indexed (x,y), they ARE NOT! Images take row and column as the indexes in that order, so you need to put y first, NOT x

II = sourceimage(y:y+h,x:x+w);

Also, your equations for x, y, w, and h are wrong.

[Khaled Al-Faleh]

Thanks sir its clear now :) .