Error: Function definition not supported in this context. Create functions in code file.

Hi I'm new to Matlab, currently using Matlab R2019b.

I was trying to write some coding for median filters, so I found this online and copy pasted it into my Matlab. I tried changing the script into function script, I've tried changing paths, separating the functions. I downloaded the Image processing tools. If i start typing the code without the word 'function', the error will be shown below.

Is there any presettings I need to do? Or anything to do before I type the code in?

This is the code I tried.

function Y = PSMF(x)
x = double(x);
WF = 3; ND = 3;T = 40;a = 65;b = -50;
M = medfilt2(x,[3 3]);
N = abs(x - M);
N(N>T)=0;
N = N ~= 0;
N = double(N);
R = sum(N(:))/(size(x,1) * size(x,2));
if R <= 0.25
    WD = 3;
else
    WD = 5;
end
TD = a + (b * R);
z = IMPDET(x,ND,WD,TD);
Y = NF(x,z,WF);
 
%% Impulse Detection
function F1 = IMPDET(x,ND,WD,TD)
X = x;
M = medfilt2(X,[WD WD]);
D = abs(X - M);
F = zeros(size(x));
F(D>=TD)=1;
F1 = F;
X(F1==F)=X(F1==F);
X(F1~=F)=M(F1~=F);
for i = 1:ND-1
    M = medfilt2(X,[WD WD]);
    F1(abs(X - M)<TD)=F(abs(X - M)<TD);
    F1((X - M)>=TD)=1;
    X(F1==F)=X(F1==F);
    X(F1~=F)=M(F1~=F);
    F = F1;
end
return;

%% Noise Filtering
function Y = NF(x,f,WF)
g = f;
Y = x;
Y1 = Y;
g1 = g;
s = sum(g(:));
while s ~= 0
    M = medfilt2(Y,[WF WF]);
    Y1(g==1)=M(g==1);
    g1(Y~=Y1)=0;
    Y = Y1;
    g = g1;
    s1 = sum(g(:));
    if s1 ~= s
        s = s1;
    else
        s = 0;
    end
end
return;

Answer 1

[Geoff Hayes]

Chew - in the above code, you are defining three functions (for each, there is the function signature and function body). These functions need to be saved to a file and the file saved somewhere in the MATLAB search path. The function keyword is used to declare a function and is not intended to be used in a function "call". When you want to call a function, you just need to pass in the parameters that this function expects. For the second error message, you haven't defined an x. You need to do this like

>> x = 42;       % 42 is just an example - I don't know what the input parameter should be
>> Y = PSMF(x);

or just call the function as

>> Y = PSMF(42);

[Chew]

Thank you so much! Now I don't get those errors anymore. But can I know how should I implement that part of the code into this?

    i=imread('cameraman.tif');
    isp=imnoise(i,'salt & pepper',0.1);
    figure,imshow(i);
   
    med=medfilt2(isp);
    figure,imshow(med);

How can I substitute this medfilt2 into PSMF?

[Geoff Hayes]

What do you want to pass into PSMF? I see (from above) that it callsn medfilt2, so do you just want to do

    i=imread('cameraman.tif');
    isp=imnoise(i,'salt & pepper',0.1);
    figure,imshow(i);
   
    med=PSMF(isp);
    figure,imshow(med);