Get coordinates of points from an image

Hello,

I would like to know how to obtain the coordinates of p number of random points from an image:

• how to call an image ( do i have to specify the path of the folder and how?)
• How to obtain the data of x axix and y axis corresponding to it

Shall i use the function getimage?

Thank you

Answer 1

[Image Analyst]

Try this:

[rows, columns, numberofColorChannels] = size(yourImage);
randomRows = randi(rows, p);
randomColumns = randi(columns, p);

Not sure what "call an image" means, but perhaps you mean imread():

yourImage = imread(fileName);

[Matthew Worker]

I have tried it with this example but apparently there is an error in the use of imread.

Also, i want the exact location of successive points stored in a vector in order to mesh the image , is there another way?

Thank you

[Image Analyst]

Do not use image as the name of a variable. It's a built-in function that you don't want to destroy.

Try

[rows, columns, numberofColorChannels] = size(yourImage);
[R, C] = meshgrid(1:rows, 1:columns); % R and C are 2-D matrices.
% To get a list of (row, column), turn into column vectors and stitch:
RC = [R(:), C(:)]; % Has all possible coordinates in the image.

[Image Analyst]

I think your "Answer" below is actually a comment to my Answer.

Yes, you can use either reshape(array, [], 1) or (:) to turn any array into a column vector. A developer at Mathworks told me that useing (:) is efficient and actually does not allocate another chunk of memory for the array. Of course if you store in in a new variable, then it will. So

m = mean(array(:))

will not create any temporary or additional memory (other than 8 bytes for "m"). But

v = array(:);

will because you now have another variable "v" that has the same number of bytes as "array".

Just a note that many people forget, matrices are not indexed like array(x, y). They are indexed array(y, x) which is array(row, column). So specifically used R and C, instead of X and Y like many people would use, so you would know to use it the correct way. So just watch out for that constantly as you use MATLAB. Some functions use or return (row, column), like find(), and some functions like (x,y), like plot().

So if my answer worked (like you said it did), please click the "Accept this Answer" link. Thanks in advance.

Answer 2

[Matthew Worker]

It works!

I have also tried to reshape the matrix C.

Thank you