How to solve the error in PSNR function?

Question

Bhavneet Sharma 2019-4-28

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/458991-how-to-solve-the-error-in-psnr-function

回答： Image Analyst 2019-12-24

There is a problem in code of image watermarkin in which DCT technique is applied: it gave error in the PSNR function as:

Error using psnr
Too many input arguments.
Error in dct1_embed (line 112)
psnr=psnr(cover_object,watermarked_image,Nc,Mc);

Code is given below:

file_name='lena.png';
cover_object=double(imread(file_name));
% determine size of cover image
Mc=size(cover_object,1);	        %Height
Nc=size(cover_object,2);	        %Width
% determine maximum message size based on cover object, and blocksize
max_message=Mc*Nc/(blocksize^2);
% read in the message image
file_name='copyright2.png';
message=double(imread(file_name));
%Mm=size(message,1);	                %Height
%Nm=size(message,2);	                %Width
[rows, columns, numberOfColorChannels] = size(message);
% reshape the message to a vector
message=fix(reshape(message,rows*columns,numberOfColorChannels)/2);
message=message(1:2000);
% check that the message isn't too large for cover
if (length(message) > max_message)
    error('Message too large to fit in Cover Object')
end
% pad the message out to the maximum message size with ones
message_pad=ones(1,max_message);
message_pad(1:length(message))=message;
% generate shell of watermarked image
watermarked_image=cover_object;
% process the image in blocks
% encodes such that (5,2) > (4,3) when message(kk)=0
% and that (5,2) < (4,3) when message(kk)=1
x=1;
y=1;
for (kk = 1:length(message_pad))
    % transform block using DCT
    dct_block=dct2(cover_object(y:y+blocksize-1,x:x+blocksize-1));
    
    % if message bit is black, (5,2) > (4,3)
    if (message_pad(kk) == 0)
        % if (5,2) < (4,3) then we need to swap them
        if (dct_block(5,2) < dct_block(4,3))
                temp=dct_block(4,3);
                dct_block(4,3)=dct_block(5,2);
                dct_block(5,2)=temp;
        end
    
    % if message bit is white, (5,2) < (4,3)
    elseif (message_pad(kk) == 1)
        
        % if (5,2) > (4,3) then we need to swap them
        if (dct_block(5,2) >= dct_block(4,3))
                temp=dct_block(4,3);
                dct_block(4,3)=dct_block(5,2);
                dct_block(5,2)=temp;
        end
    end
    
    % now we adjust the two values such that their difference >= k
    if dct_block(5,2) > dct_block(4,3)
        if dct_block(5,2) - dct_block(4,3) < k
            dct_block(5,2)=dct_block(5,2)+(k/2);
            dct_block(4,3)=dct_block(4,3)-(k/2);            
        end
    else  
         if dct_block(4,3) - dct_block(5,2) < k
            dct_block(4,3)=dct_block(4,3)+(k/2);  
            dct_block(5,2)=dct_block(5,2)-(k/2);
        end
    end
        
    % transform block back into spatial domain
    watermarked_image(y:y+blocksize-1,x:x+blocksize-1)=idct2(dct_block);    
    
    % move on to next block. At and of row move to next row
    if (x+blocksize) >= Nc
        x=1;
        y=y+blocksize;
    else
        x=x+blocksize;
    end
end
% convert to uint8 and write the watermarked image out to a file
watermarked_image_int=uint8(watermarked_image);
imwrite(watermarked_image_int,'dct1_watermarked.bmp','bmp');
% display processing time
elapsed_time=cputime-start_time;
% display psnr of watermarked image
psnr=psnr(cover_object,watermarked_image,Nc,Mc);

what will be the alternative of it means who to solve this problem?

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marie lasz 2019-12-24

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Answer 1

Image Analyst 2019-12-24

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/458991-how-to-solve-the-error-in-psnr-function#answer_407623

Just like the error message says, psnr() does not take that many input arguments. You passed in 4 and it can take only up to 3. Why are you passing in the image width and height??? It doesn't want those.

Here is the usage from the help:

Description

example