regarding cropping a polygon out of an image

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ramakrishna bathini 2011-2-22

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hi folks can anybody help me with cropping a polygon out of the image?

i used the following code

I=dicomread('100.ima');
figure,imshow(I,[]);
h=impoly;
position=wait(h);

its providing the option for configuring the required polygon.i have also said it to copy figure.

how can i see only the cropped image?

can anyone help with imcrop()to see the output

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Answer 1

Jan 2011-2-24

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在 MATLAB Online 中打开

Do not use

imshow(x(~bw), []);

but

imshow(x, []);

"x(~bw)" is a vector and IMSHOW must fail.

What is the problem with the 2nd part of your program? If you just want to apply the IMCROP once, use something like "if z==1".

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ramakrishna bathini 2011-2-24

编辑：Walter Roberson 2012-8-26

在 MATLAB Online 中打开

clear all;
close all;
clc
I=dicomread('100.ima');
[x,y,I2,rect]=imcrop(I,[]);
figure,imtool(I,[]);
figure,imtool(I2,[]);
m=143;
imstack=zeros(512,512,m);
for z=1:m;
    n=dicomread([num2str(z),'.ima']);
    n=imcrop(n,rect);
    M=shrinkWrap(n,'objthresh',15000,'biggest');
    Ipore=n<400&M;
    imstack(:,:,z)=Ipore;
end
y=double(imstack);  
D = squeeze(y);
  h = vol3d('cdata',D,'texture','2D');
  view(3); 
  Update view since 'texture' = '2D'
  vol3d(h);  
  axis tight;  daspect([1 1 .4])
  alphamap('rampup');
  alphamap(.06 .* alphamap);

Thanks a bunch for your help.This is the complete code that is working..the code is asking only once for cropping and then applying those dimensions to all the 143 images and popping the output..

Jan 2011-2-25

Does this mean, that you accept the answer?

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Answer 2

Jan 2011-2-22

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Do you want to crop a rectangle from the image? Or mask a polygone?

figure
img = imread('pout.tif');
imshow(img);
h = impoly;
position = wait(h);
x1 = min(position(:, 1));
x2 = max(position(:, 1));
y1 = min(position(:, 2));
y2 = max(position(:, 2));
BW = createMask(h);
img(~BW) = 255;
img = img(x1:x2, y1:y2);
% Or if img is a 3D RGB array:
% img(~cat(3, BW, BW, BW)) = NaN;
% img = img(x1:x2, y1:y2, :);
figure;
image(img);

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ramakrishna bathini 2011-2-24

sorry for not being clear...i mean the code line img(~BW) is throwing the output of thin strip of line...

clear all;

x=dicomread('100.ima');

imshow(x,[]);

h=impoly;

position=wait(h);

x1=min(position(:,1));

X2=max(position(:,2));

y1=min(position(:,1));

y2=max(position(:,2));

bw=createMask(h);

imtool(bw);

x(~bw)=255;

imshow(x(~bw),[]);

this is the code i used.the output of imtool(BW) is a white rectangular box with black background.this is the mask.....now i want to apply this mask on the original image to get the cropped output image...next thing is to apply this to 140 images in a loop...

clear all;

close all;

clc

I=dicomread('100.ima');

[x,y,I2,rect]=imcrop(I,[]);

figure,imshow(I,[]);

figure,imshow(I2,[]);

m=143;

imstack=zeros(512,512,m);

for z=1:m;

n=dicomread([num2str(z),'.ima'];

[x,y,n,rect]=imcrop(n,[]);

M=shrinkWrap(n,'objthresh',15000,'biggest');

Ipore=n<400&M;

imstack(:,:,Z)=Ipore;

end

this line is able to do the rectangular cropping i need poly cropping instead. [x,y,I2,rect]=imcrop(I,[]);

but i am making changes to above code as well bcoz its asking for dimension for the second time in the loop..i jst want to take the dimensions for the first time and apply it to everything.

manoj sambasivam 2012-5-16

Hi Jan simon,i have small doubt sir, regarding the program.after i select the polygon , what should i do to crop the polygon out of image and save it separetely?

Image Analyst 2012-5-16

You do know that images have to be rectangular, don't you? You do know that you can't have a polygonal image, right? (Looks like your answer would be "no") Even if the information is in a polygon shape, you still have to have something (like zeros) to make it a rectangular image.

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Answer 3

Alex Taylor 2012-5-16

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在 MATLAB Online 中打开

Also, if you DO intend to apply a polygon mask to an image, there are easier ways of doing it. The function roipoly is designed for interactively creating a mask of an arbitrary polygon:

doc roipoly

For example:

I = imread('pout.tif');
imshow(I);
BW = roipoly
Imasked = zeros(size(I),class(I));
Imasked(BW) = I(BW);
imshow(Imasked)

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vidya 2012-9-10

Maria,

I am looking for an answer to your second question, were you able to find a solution, if yes can you share, if not can someone help me too. I also am trying to find a method that can help process only selected image pixels within a polygon for colored images, -Many thanks for your help

Image Analyst 2012-9-10

It depends on what kind of process you want to do: area processes and point processes would be done in different ways. Area processes (like blurring) need masking while point processes don't necessarily need extra masking steps (for example taking the average = mean(grayImage(maskImage))). Why don't you start a new thread and upload your image and tell us what you want to measure?

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