% These are file comments.

% If you are not certain what a MATLAB function does, type 
% >> help fName 
% at the console window.  Alternately, you can use the online help.

% The first line for an m-file function begins with (something like)
function r = fName(a1)
% r is a return value, fName is the function name and a1 is the argument
% This function is called from the console with
% >> x = fName('im1.tiff');
 
% This next statement reads the image data in from the image file.
% It is assumed that a1 is in a string format, e.g. 'im.tiff'
im = imread(a1,'TIFF');
% This statement displays the image
imagesc(im);
% If the image is grayscale, you will need to change the colormap as below
colormap gray;

% Gets a single mouse click input from the figure
[x,y,b] = ginput(1)
% Leaving off the semicolon causes the values to stream on the console window.
% This is useful for debugging

% The size function returns the number of rows/cols in an array
[row,col] = size(im);

% This is the format for a "for" loop.
% This loop sets all of the elements of the first column to 0
for i=1:row
    % Parentheses are the array operator, and it is (row,col) format
    im(i,1)=0;
    % All code blocks must end with "end"
end

% You could achieve the same effect by doing
im(1:end,1)=0;
% Or
im(:,1)=0;
% These are MUCH FASTER than using for loops.  

% This loop demos the "if-else" statement.  The else part is optional.
for i=1:col
    if im(1,i)>100
        im(1,i) = 255;
    else
        im(1,i) = 0;
    end
end

% Again a MUCH faster implementation would be
im(1,:) = 255*(im(1,:)>100);

% Dummy assignment for return value
r = 0;