How can I find X smallest numbers in a Matrix?

I have a 480 by 640 matrix, and I would like to find 4 smallest number ( or closest values to zero).

Answer 1

[Matt J]

 Xs=sort(X(:));

 FourSmallest = Xs(1:4);

[Matt J]

There are also more optimized routines on the FEX, e.g.,

http://www.mathworks.com/matlabcentral/fileexchange/23576-minmax-selection

[Laila Kazemi]

will I also be able to obtain indices of the values in this method?

[Matt J]

Of course!

[Laila Kazemi]

How?

[Laila Kazemi]

when I try:

 [Xs Xind]=sort(X(:));

in Xind it return the indices as one number

[Image Analyst]

You may have more than 4 pixels having the 4 smallest values. You can use ind2sub() or find

[rows1, columns1] = find(yourImage == Xs(1));
[rows2, columns2] = find(yourImage == Xs(2));
[rows3, columns3] = find(yourImage == Xs(3));
[rows4, columns4] = find(yourImage == Xs(4));

[Matt J]

in Xind it return the indices as one number

In case it matters, note that the "one number" will work as an index, even when used with the original 480x640 matrix, e.g.,

>> X=reshape((1:20)*10,4,5).'

X =

      10    20    30    40
      50    60    70    80
      90   100   110   120
     130   140   150   160
     170   180   190   200

>> [Xs, Xind]=sort(X(:));  

>> X(Xind(4))

ans =

      40