Extract and show non zero pixels of a 2D image in MATLAB

Hello,

I have an image ima;

of size 256x96; I use find( ) to find the nonzero pixels' linear indices

indd=find(ima);
[row col]=ind2sub(size(ima),indd);

and I get two vectors,

row;
col;

How to show this new image, using imagesc ?

[Matt J]

I use find( ) to find the nonzero pixels' linear indices

It is unnecessary to use ind2sub here. You can use find() to get the subscripts directly,

[row col]=find(ima);

How to show this new image

In what way are the row, col vectors to be considered an "image"?

[sn at]

What I think now is that the only way to be able to show this, is the same size as the original image, with all the zero pixels there.

Answer 1

[Matt J]

The question seems very open ended. Perhaps as follows,

spy(ima)

[sn at]

thank you, this shows the nonzero pixels (which is the mask), but it does not have any output to be able to proceede with it.

Answer 2

[Image Analyst]

Just tell us what you really want to do. If you just want to look at the image you'd use

imshow(ima);

That will show only non-zero pixels because the zero ones will show up as black.

If you want a list of them, you can use find() and that gives you a list of coordinates.

[rows, columns] = find(ima);

Now you have two vectors with the locations of the non-zero pixels. If you want them in an N-by-2 matrix of (x,y) coordinates, you can do

xy = [columns(:), rows(:)]

So that gives you basically everything you need. But we don't know what you really have in mind. You can't have an image show up where the zero pixels are like "holes" in the figure and you can see whatever is on your computer behind the figure as if the zero pixels were 100% transparent. And there is really no need for that anyway. So what do you really want to do? Do you just want to do some operation, like blurring or whatever, on the non-zero pixels? If you could do whatever you're thinking of, what would be the next step. You said you need an "output to be able to proceede with it.' Well, what does "proceede" mean to you? Do you want to measure intensity? Area of particles? What???