The output of the function is unrecognized in the function

Write a function to "smooth" a black and white image by replacing each pixel by the average of itself and its neighbors. In MATLAB a black and white image is just a matrix of 1s and 0s - 1 represents white, and 0 represents black. To keep the algorithm simple, ignore the edges of the image - that is, do not change the first and last rows and columns.

function name = smooth_image

input argument = input matrix

output argument = output matrix

the algorithm can be described as follows:

- Given a NxM input matrix

- Make a copy of the matrix - this will be the output matrix

- loop over rows 2 to N-1 on the input matrix

- loop over columns 2 to M-1 of the input matrix

- take the average of the 3x3 submatrix centered on the current row & column

- set the corresponding element of the output matri equal to this average

This is what I have so far: (but it keeps returning "unrecognized function or variable 'output'. Error in smooth_image (line 2). input = output;

function output = smooth_image(input)
input = output;
N = length(input(1,:));
M = length(input(:,1));
for i = 2:N-1
    for j = 2:M-1
        A = input(i,j);
        A = mean(i-1:i+1,j-1:j+1);
        output = A(i,j);
    end
end
end

[per isakson]

Did you mean

output = input;

rather than

input = output;

?

[Walter Roberson]

Notice that every iteration you are overwriting ALL of A with a scalar value.

Answer 1

[Bhargavi Maganuru]

Error is because of assigning output of the function to a variable in the 1st line itself. Notice that you’re calculating the mean to the indices and not to the submatrix in the loop.

You can use following code

function output = smooth_image(input)
output = input;
N = length(input(1,:));
M = length(input(:,1));
for i = 2:N-1
    for j = 2:M-1
        A = mean2(input(i-1:i+1,j-1:j+1));
        output(i,j) = A;
    end
end
end