Unrecognized function or variable 'delta'.

%function fn = retrieve(X,irow,icol);
watermark = imread('watermark.jpg');
watermark=imresize(watermark,[32 32]);

watermarked_img = imread('watermarked_img.jpg');
[irow icol dim] = size(watermark);
watermark=rgb2gray(watermark);
watermark=im2bw(watermark,0.5);
w = reshape(watermark,irow*icol,1);   
X=[];
rng(1,'twister');
for i=1:size(w,1)
    for j=1:7
        r_range=[5 507];
        x=randi(r_range,1,1);
        y=randi(r_range,1,1);
        temp=[];
        a=delta(watermarked_img,x,y);
        temp=[double(a)];
        for j=-2:2
            if(j~=0)
                temp=[temp ; double(delta(watermarked_img,x+j,y))];  
            end
        end
        for j=-2:2
            if(j~=0)
                temp=[temp ; double(delta(watermarked_img,x,y-j))];  
            end
        end
        X=[X double(temp)];
    end
end
%%%%%%%%%%%%%%%%%%%%%%
global net
out=net(X);
%count1=0;
for i=1:size(out,2)
    if(out(i)>0)
        out(i)=1;
        %count1=count1+1;
    else
        out(i)=0;
    end
end
j=0;
out2=[];

'bbbbbbbbbbbb'
size(out,2)
for i=[1:7:size(out,2)]
    j=j+1;
    t=[out(i) out(i+1) out(i+2) out(i+3) out(i+4) out(i+5) out(i+6)];
    out2(j)=mode(t);
    
end

irow
icol
size(out2,2);
w = reshape(out2,irow,icol);   
[w map]=gray2ind(w,255);
imwrite(uint8(w), 'retrieve.jpg'); 
I = imread('retrieve.jpg'); 
imshow(I)
accuracy();
% T = imread('watermark.jpg'); 
% imshow(T)
% 

[madhan ravi]

There’s no such function as delta(). You should define your own.

[Mostfa Abd El-Aziz]

Dear madhan ravi thanx for your response

kindly, how to define this function ??

[Dyuman Joshi]

We can't tell you that because we do not have any information as to what the code is supposed to do or what you want to do.

In case you are asking how to define a function, refer to this - function

Answer 1

[Ayush]

Hi @Mostfa Abd El-Aziz

I understand that you are getting unrecognized function of variable error. The error you are encountering is due to the use of delta, which is not defined as a function in the MATLAB code you have provided. It appears that delta is meant to be a custom function that you are using to process the image at specific pixel coordinates (x,y). You need to define this function or replace it with the correct MATLAB function that performs the intended operation.

Here is how you can define your own custom functions in MATLAB: https://www.mathworks.com/help/matlab/ref/function.html

Thanks,

Ayush