How do I fix a "Subscripted assignment dimension mismatch."

clc
c=1;
t=1;

% To read in the watermarked image

[watermarked_image cmap]=imread('lsb_image.bmp');

watermarked_image=double(watermarked_image);

% To measure the size of the watermarked_image
watermarked_image_size=size(watermarked_image);
x=watermarked_image_size(1);
y=watermarked_image_size(2); 
z=watermarked_image_size(1);

% To convert the watermarked image from a MxN matrix into a row
for a=1:watermarked_image_size(1,1)
  watermarked_image_row(1,c:z)=watermarked_image(a,1:y);
  c=c+y;
  z=z+y;
end

When I run it I get the following error:

??? Subscripted assignment dimension mismatch.

Error in ==> single_decode at 15
watermarked_image_row(1,c:z)=watermarked_image(a,1:y);

Can anybody help me remove this error? I am using a test image of size 256*256 and lsb_image.bmp of 12*9.

Answer 1

[Jan]

There is no need to use a complicated FOR loop to get a matrix as row vector:

[watermarked, cmap] = imread('lsb_image.bmp');
watermarked = double(watermarked);
watermarked_row = reshape(transpose(watermarked), 1, numel(watermarked));

EDITED: And together with Sean de's addition: If you image is a [Width x Height x 3] 3D array, convert it to a grey scale at first:

watermarked = rgb2gray(watermarked);

Or operate on a single color channel only, e.g. red:

watermarked = rgb2gray(:, :, 1);

Answer 2

[amitesh kumar]

%This program decode the watermark from the single embed watermarked image clc c=1; t=1; %To read in the watermarked image [watermarked_image cmap]=imread('lsb_image.bmp'); watermarked_image=double(watermarked_image); %To measure the size of the watermarked_image watermarked_image_size=size(watermarked_image); x=watermarked_image_size(1); z=watermarked_image_size(1); y=watermarked_image_size(2); %To convert the watermarked image from a MxN matrix into a row

[watermarked, cmap] = imread('lsb_image.bmp'); watermarked = double(watermarked); watermarked_row = reshape(transpose(watermarked), 1, numel(watermarked));

if i am directly replacing your code with previous one by removing for loop, than i am getting following error

??? Error using ==> transpose Transpose on ND array is not defined.

Error in ==> single_decode at 16 watermarked_row = reshape(transpose(watermarked), 1, numel(watermarked));

have u any idea how to remove this error..and y this error is occurring. plz help me

[Doug Hull]

please add this as a comment to the original question or an answer. It should not be an answer by itself. You can delete it after moving it.

Answer 3

[Sean de Wolski]

probably have to do:

 watermarked_image = rgb2gray(watermarked_image);

then Jan's reshape call

[amitesh kumar]

but i am using gray image only....

[Walter Roberson]

After the imread() statement, put in

disp(ndims(watermarked))

and tell us what it reports.

Why are you reading the same image twice? Once into watermarked_image and once into watermarked ?

[Jan]

There are 2 kinds of gray scale images: 1. just the colors are gray, but they are saved as RGB values, 2. the JPEG has a gray scale "color" table and used index colors. As Walter suggested, you can distinguish them by inspecting the reply of IMREAD.