How to convert a for loop script into a function

Im=imread('Untitled23.png');

figure,imshow(Im);
title('Original Image');

%0.2989 * R + 0.5870 * G + 0.1140 * B 
GIm=uint8(zeros(size(Im,1),size(Im,2)));
for i=1:size(Im,1)
      for j=1:size(Im,2)
          GIm(i,j)=0.2989*Im(i,j,1)+0.5870*Im(i,j,2)+0.1140*Im(i,j,3);
      end
end

%Specifically im turning a regular image into grayscale, feel free to test my function :), but how do i convert it into a function.

Answer 1

[Image Analyst]

In ConvertToGrayscale.m, have this:

function grayImage = ConvertToGrayscale(filename)
  grayImage = []; Initialize to null
  if ~exist(filename, 'file')
    message = sprintf('Image file not found:\n%s', filename);
    uiwait(warndlg(message));
    return;
  end
  originalImage = imread(filename);
  [rows, columns, numberOfColorChannel] = size(originalImage);
  if numberOfColorChannel > 1
    grayImage = rgb2gray(originalImage);
  else
    grayImage = originalImage;
  end

It could be made more robust (like using try/catch, checking for indexed images, etc.), but this is a good start. And I didn't test it, it's just off the top of my head, so you may have to do a little debugging (fix typos or whatever).