Basic: calling a function

I have a probably very basic question:

I have made a function file in matlab and want to call it within my script file. The script is not finished, so I just need to consentrate to get the function "central_difference" working for now. I get an error message saying that the variable 'greyimg' is not defined when I call central_difference. I don´t understand why, since it is defined....? And when the function works, should it not also be able to plot the subplots 152-154

Code here:

Script file:

clc;
clear all;
 
gridimg = im2double(imread('grid.jpg'));
grayimg = rgb2gray(gridimg);
 
[Ix,Iy,Im]  = central_difference(greyimg);
[x,y,theta] = extract_edges(Ix, Iy, Im, edge_threshold);
 
figure(6);
set(gcf,'Position',[100 100 1000 300])
subplot(151); imshow(img_blur);            xlim([300, 500]); title('Blurred input');
subplot(152); imshow(Ix, [-0.05, 0.05]); xlim([300, 500]); title('Gradient in x');
subplot(153); imshow(Iy, [-0.05, 0.05]); xlim([300, 500]); title('Gradient in y');
subplot(154); imshow(Im, [ 0.00, 0.05]); xlim([300, 500]); title('Gradient magnitude');

Function file:

function [Ix, Iy, Im] = central_difference(Img)
    Ix = zeros(size(Img)); % Placeholder
    Iy = zeros(size(Img)); % Placeholder
    Im = zeros(size(Img)); % Placeholder
    
    kernel = [1/2 0 -1/2];
    
    for i=1: size(Img, 1)  %alle rader i grayimg
    Ix(i, :) = conv(Img(i,:), kernel, "same");  %conv med kernel
    end
 
    for  j=1: size(Img, 2) %alle kolonner i grayimg
    Iy(:, j) = conv(Img(:,j), kernel, "same");
    end 
    
    Im = sqrt(Ix.^2 + Iy.^2);
end

Answer 1

[Cris LaPierre]

The error is telling you that greyimg does not exist. When you create the variable, you call it grayimg (with an a instead of e)

grayimg = rgb2gray(gridimg);
  ^ % gray
[Ix,Iy,Im]  = central_difference(greyimg);
                                   ^ % grey

[Stina Ravdna Lorås]

And so basic could it actually be :D

Obviously too tired. Thought I had misunderstod the consept of functions. Thank you!