Matrix dimensions must agree. Error in pre (line 146) inv_trans_​img(:,l)=v​{m-1}.*tra​ns_img(:,l​);........​......I am getting this error if anybody would help me to sortout this then it will be a goodhelp

if true
  % code
endclear all
close all
clc
[filename, pathname] = uigetfile('*.bmp', 'Pick an M-file');
if isequal(filename,0) || isequal(pathname,0)
  warndlg('Image is not selected');
else
  a=imread(filename);
  figure(1)
  imshow(a)
  a=rgb2gray(a);
  figure(2);
  imshow(a)
  title('converted image from rgb to gray')
  a=imresize(a,[512,512]);
  figure(3)
  imshow(a,[])
  title('cover image')
  a=im2double(a);
  %imshow(a);
end
[filename, pathname] = uigetfile('*.bmp', 'Pick an M-file');
if isequal(filename,0) || isequal(pathname,0)
  warndlg('Image is not selected');
else
  secret=imread(filename);
  %imshow(secret);
  figure(4)
  imshow(secret,[])
  title('Watermark Image')
end
m=1;
% k=30;
for i=1:8:256
  for j=1:8:256
      for x=0:7
          for y=0:7
              img(x+1,y+1)=a(i+x,j+y);
          end
      end
      k=0;    
      for l=1:8
          img_expect{k+1}=img(:,l)*img(:,l)';
          k=k+1;
      end
      imgexp=zeros(8:8);
      for l=1:8
          imgexp=imgexp+(1/8)*img_expect{l};%expectation of E[xx']
      end
      img_mean=zeros(8,1);
      for l=1:8
          img_mean=img_mean+(1/8)*img(:,l);
      end
      img_mean_trans=img_mean*img_mean';
      img_covariance=imgexp - img_mean_trans;
      [v{m},d{m}]=eig(img_covariance);
      temp=v{m};
      m=m+1;
      for l=1:8
          v{m-1}(:,l)=temp(:,8-(l-1));
      end
      for l=1:8
          trans_img1(:,l)=v{m-1}*img(:,l);
      end
      for x=0:7
          for  y=0:7
              transformed_img(i+x,j+y)=trans_img1(x+1,y+1);
          end 
      end
  end
end
% transformed image is assigned to cover_object
cover_object=double(transformed_img);
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;
% read in the message image
message=double(secret);
Mm=size(message,1);                  %Height
Nm=size(message,2);                  %Width
% reshape the message to a vector
message=round(reshape(message,Mm*Nm,1)./256);
% 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's
message_vector=ones(1,max_message);
message_vector(1:length(message))=message;
% generate shell of watermarked image
watermarked_image=cover_object;
% read in key for PN generator
file_name='_key.bmp';
% key=double(imread(file_name))./256;
% reset MATLAB's PN generator to state "key"
rand('state',35);
% generate PN sequence
pn_sequence_zero=round(2*(rand(1,sum(sum(512)))-0.5));
pn_sequence_one=round(2*(rand(1,sum(sum(512)))-0.5));
% process the image in blocks
%x=1;
%y=1;
for kk = 1:length(message_vector)
  % transform block using DCT
  dct_block=(cover_object(1:256,1:256));
  % if message bit contains zero then embed pn_sequence_zero into the mid-band
  % componants of the dct_block
  ll=1;
 if (message_vector(kk)==0)
      for ii=1:256
          for jj=1:256
              if (dct_block(jj,ii)==1)
                  dct_block(jj,ii)=(dct_block(jj,ii))+k*pn_sequence_zero(ll);
                  ll=ll+1;
              end
          end

        end
   else
        for ii=1:256
            for jj=1:256
                if (dct_block(jj,ii)==1)
                    dct_block(jj,ii)=(dct_block(jj,ii))+k*pn_sequence_zero(ll);
                    ll=ll+1;
                end
            end
        end   
   end        
            % transform block back into spatial domain
  %  watermarked_image(1:256,1:256)=((dct_block));
    % move on to next block. At and of row move to next row
%  %   if (x+512) >= Nc
%         x=1;
%         y=y+512;
%     else
%         x=x+512;
%     end
end
 mask=[1 1 1 1 
       1 1 1 1
       1 1 1 1
       1 1 1 1 ];
trans_img=dct_block'.*1;
for l=1:256
    inv_trans_img(:,l)=v{m-1}.*trans_img(:,l);
end
for x=0:3
    for  y=0:3
        inv_transformed_img(i+x,j+y)=inv_trans_img(x+1,y+1);
        imwrite(uint8(inv_transformed_img),'Lena_wtermarked_image.bmp','bmp');
    end
end
figure(5)
imshow(transformed_img);
title('transformed image')
figure(6)
imshow(inv_transformed_img);
title('inverse transformed image')
% imwrite(uint8(inv_transformed_img),'Lena_wtermarked_image.bmp','bmp');
figure(7)
LWI=imread('Lena_wtermarked_image.bmp');
imshow(LWI);
title('Watermarked Image')

[madhan ravi]

File/s??

[PromoCodeBSJ]

Well all it means is your matrix dimensions aren't the same so you can't perform the operation. Check the dimensions of the matrix inv_trans_image and trans_image

[shivu P]

checked both are different ....how to equalize and prform the operation

[Walter Roberson]

I doubt that anyone will read the code thoroughly and work through the undocumented mathematical operations and mentally work backwards to figure out what a useful set of operations would be instead and tell you the appropriate code, all without even having your test image.