The use of Nargin in Otsu Image Processing

I was actually given the full code to use from my professor and all I had to do was process it with a couple of photos. However I'm running into a few problems with the given code and I've tried to understand why it's not working but I think I could use some help. Here it is:

This is the function I think?

%Otsu Thresholding

% [ot,outim]=otsu_thresh(im)

%   where im is the grey image (integer 0-255)

%       Otsu Thresholding is performed on the image

%   ot is the threshold determined

%   outim is the image after thresholding

   if nargin<1
  im=mean(double(imread('10um.jpg')),3);
  else
  if max(max(imread('10um.jpg')))<=1
  im=round(im.*255);
  end
  end
  [height,width]=size(im);
  pixels=height*width;
  bins=[0:255]+0.5;
  N=hist(reshape(im,pixels,1),bins);
  Nnorm=N/sum(N); %normalising the bin frequencies to make probabilities
  theta=cumsum(Nnorm); %cumulative probability
  mu=cumsum(Nnorm.*[0:255]);
  %Repeat on the image
  sigB2=(mu-mu(256)*theta).^2./(theta.*(1-theta)); %evaluate sigB2 over the t range
  [p ot]=max(sigB2); %find the maximum value and the index where it is (this is the Otsu threshold)

and this is the script im supposed to run:

x=(im>ot); %thresholding

figure(1)

imshow(x)

figure(2)

imshow(x)

hist(x);

(I believe there is 0 problems with the actual script just the function)

Answer 1

[Image Analyst]

You're not using the im that was passed in - you're just overwriting it with some predefined image. Try this:

if nargin < 1
  im = mean(double(imread('10um.jpg')),3);
else
  if max(im(:)) <= 1
    % Scal to max possible gray level for its class if it's less than 1.
    maxPossibleValue = double(intmax(class(im)))
    im = round(maxPossibleValue * double(im));
  end
end

[Michael Yabut]

And sorry to bother you im unclear on what it means when it says nargin needs to be declared in a function how do I clear that up?

[Walter Roberson]

You need to put that code inside a "function" -- that is, a .m file that starts with the word "function". nargin is not permitted inside a script (that is, at the command line, or in a .m file that does not start with either "function" or "classdef")

I suggest you just use

if max(im(:)) <= 1
    % Scal to max possible gray level for its class if it's less than 1.
    maxPossibleValue = double(intmax(class(im)))
    im = round(maxPossibleValue * double(im));
  end

without the nargin test.

[Image Analyst]

For some reason you commented out the function line. Put it back in:

function [ot,outim]=otsu_thresh(im)