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

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amitesh kumar
amitesh kumar 2011-2-2
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.

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回答（3 个）

Jan
Jan 2011-2-2
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);
amitesh kumar
amitesh kumar 2011-2-2
%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
  1 个评论
Doug Hull
Doug Hull 2011-2-2
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.

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Sean de Wolski
Sean de Wolski 2011-2-2
probably have to do:
watermarked_image = rgb2gray(watermarked_image);
then Jan's reshape call
  3 个评论
显示 1更早的评论
Walter Roberson
Walter Roberson 2011-2-6
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
Jan 2011-2-6
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.

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