Matrix Dimensions Must Agree

Hello I'm new to mathlab and I'm facing this issue. I'm gonna making image watermarking using dct method and this is my code, hope i can find the solution of this, thankyou beforeee

clc;
clear all

I=imread('Sunset.jpg'); I=imresize(I,[300 300]);
if size(I,3)==3
    I=rgb2gray(I);
end
figure,imshow(I), title('CITRA Penampung')

W=imread('copyright1.png'); I=imresize(I,[300 300]);
if size(W,3)==3
    W=rgb2gray(W);
end
figure,imshow(W), title('CITRA Watermark')

alpha = 0.02;
A = dct2(double(I));
B = dct2(double(W));
C = A + alpha*B;
Iw = round(real(idct2(C)));
IIw = uint8(Iw)
figure,imshow(IIw), title('CITRA Terwatermark')

I=imread('Sunset.jpg'); I=imresize(I,[300 300]);
if size(I,3)==3
    I=rgb2gray(I);
end
A=dct2(double(I));
C1=dct2(double(Iw));
B1=(C1-A)./alpha;
W1=uint8(idct2(B1));
figure,imshow(W1), title('CITRA Watermark Hasil Ekstraksi')

%this is the error I get
Matrix dimensions must agree.

Error in dctcoba (line 19)
C = A + alpha*B;

Answer 1

[per isakson]

Is this a copy&paste error?

W=imread('copyright1.png'); I=imresize(I,[300 300]);

Replacing the line by

W=imread('copyright1.png'); W=imresize(W,[300 300]);

might help.

[Mesita Widia Cahyaning]

ohmygod.. my eyes:( thankyou! been replacing the line but now im facing another error:( what is this, can you help me:(

Matrix dimensions must agree.

Error in dct (line 76)
  b = W .* fft(y);

Error in dct2 (line 49)
    b = dct(dct(arg1).').';

Error in dctcoba (line 17)
A = dct2(double(I));

[per isakson]

My standard answer is: see Debug a MATLAB Program and Examine Values While Debugging

Run dbstop if error in the command window and start your script.

I failed to reproduce your error with R2018b. I used the first jpg-file I found on my computer. Your script produced four figures and ended without any messages.

Here all variable values are <300x300 double> (except for alpha) after the script finished!

[Mesita Widia Cahyaning]

Hello! Thankyou for trying out my codes! (: but I dont know why I still get the same error and also get different values for every variable.. What im supposed to do then:(

[Walter Roberson]

Put a breakpoint in at dctcoba line 17, at the call to dct2. Run. Then tell us what size(I) is

Question: why do you read in Sunset twice ?

[Mesita Widia Cahyaning]

Oh yes, I think I dont really need to re-read Sunset in line 24, and now I'm deleting it.

Done put a breakpoint and this is the values I get:

I = 300x300x3 uint8

W = 512x512 uint8

[Walter Roberson]

What is your current code?

[per isakson]

The line number and the code of the error message doesn't agree with the code of your question. We are thus running diffent codes.