How do I stop a function from displaying output matrix without using semicolon in command window?

Here is one of my functions for color histogram equalization:

function [ newimg ] = oldhist( img );

Red = img(:,:,1);

Green = img(:,:,2);

Blue = img(:,:,3);

R = histeq(Red);

G = histeq(Green);

B = histeq(Blue);

newimg= cat(3,R,G,B);

imshow (newimg);

end

If I use it without a semicolon in the command window it will display the newimg matrix. How do I store newimg matrix without displaying the matrix and without using a semicolon in the command window?

[Shashank Prasanna]

Why don't you want to use the semicolon? It exists so that you can suppress command line output.

[James]

I thought the professor wanted the out put just to be the image not the matrix. I talked to him today and he said what everyone here has, that just putting a semicolon after it will work.

Answer 1

[Honglei Chen]

Try using

function varargout =

instead of

function newimg =

[Walter Roberson]

Then it will not return newimg to the calling function.

[Honglei Chen]

You can do the following in the code if you want to return newimg

if nargout
  varargout{1} = newimg;
end

Then unless you specify the output, it won't display.

[Walter Roberson]

True. But that will not store newimg as required by the user.

I interpret the question as requesting that

var = oldhist( TheImageArray )

must store into var but must not display the result, as if a semi-colon had been given after the command.

I do not know why the user requests this. My best guess at the moment is that the user wants to be able to turn off output to the command window without editing the source of the calling routine.

[Honglei Chen]

Oh I see, then I understand the question wrong. In that case I don't know the answer and adding a ; seems to be the best solution for me.

Answer 2

[Walter Roberson]

When you call a function that returns a value, the value will be displayed unless the context specifically instructs otherwise (such as with a semi-colon), or unless the context uses the returned value in a calculation in a way that does not display the evaluated value. For example,

if oldhist( img )
end

will use the value output by oldhist() to test for the "if" and will not display the value. Note this particular multi-line form does not use a semi-colon.

It is not possible in a MATLAB routine to find out the name of an output variable.

You could recode as

function oldhist(img, newimgvar )
   ....
   assignin('caller', newimgvar, newimg);

where newimgvar is a string indicating the name of the variable to assign into. For example,

oldhist( eye(5), 'MyResult' )

This is not recommended and will fail if the calling workspace is a static workspace (that is, there is an "end" statement matching its "function" statement.)

If you were hoping for something like a command

displayoutputs off

then there is no such command in MATLAB.