How to make points on the contour of the picture?

Dear all,

I tried to make points on the contour of the picture, like this:

This is my contour of picture:

Because I would like to after that create FEM model of this picture (contour).

This is my code:

clc;close all;clear all;

grayImage = imread('thorax-mdl.jpg');
[rows, columns, numberOfColorChannels] = size(grayImage);
if numberOfColorChannels > 1
  grayImage = grayImage(:, :, 2); 
end
mask_pater = grayImage > 220;
figure(3)
imshow(mask_pater);

contour(mask_pater,1,'b', 'LineWidth',4);

Thank you for your answers.

[KSSV]

You should have attached the image...

[Veronika]

Sorry, I forgot. Here is the image.

Answer 1

[Image Analyst]

Lower your threshold and then call bwperim() or bwboundaries().

[Veronika]

I can´t lower my threshold, because I want exactly this value of threshold.

[Image Analyst]

Then you will not get the lungs and body. You will get exactly what you are getting.

[Veronika]

I tried bwperim(), but no points in the image. I just want points of contour. I don´t need lungs and body.

[Image Analyst]

If you don't change what you do, then you won't change what you get. Why are you insisting on using a threshold that won't get you what you want?

[Veronika]

I´m not insisting on using a threshold. I thought, that there isn´t any other option for getting contour. So I used threshold. Now I have this image:

And I want to something like this:

Is that possible or I did everything wrong?

[Image Analyst]

Wait a minute. I thought this is what you wanted to make:

[Veronika]

No, I just wanted you to understand that I want to create points on the contour. Sorry for my bad expression.

[Image Analyst]

You can use bwboundaries() to get an x,y coordinate of every point on every perimeter. You can subsample that if you want. See attached demo file, test1.m below this image it creates.

[Veronika]

Okey, I tried this demo, but this error message was appeared:

Undefined function 'bwareafilt' for input arguments of type 'double'.

Error in test_demo_points (line 44)
binaryImage = bwareafilt(binaryImage, 10);

Do I have this line in my code?

[Image Analyst]

OK, just take that line out.

It's because you have a version older than R2014b.

It's not absolutely necessary - it just makes sure you aren't getting the perimeter of small noise particles.

[Veronika]

OK, but this obviously does not apply to my contours. Because I don´t want to use binaryimage.

[Image Analyst]

(Sigh) Veronika, yes you do. You do need to use a binary image. Don't you remember that you said you had to use a threshold of exactly 220? Well, what does that do? It creates a binary image.

Alright, I did it for you. Just look at the code attached below the images it creates.

See -- the outlines are exactly around the small really bright blobs which you wanted. These regions are from the binary image you got when you thresholded at 220. I even put the little circles on the boundaries like you wanted.

[Veronika]

Thank you VERY much!