How to divide gray scale image into 8x8 blocks and access each block separately to apply dct2 on the block
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Ari M Salih
on 29 Apr 2019
Edited: Image Analyst
on 23 Oct 2021
I want to divide the grayscale image which in my case is the 'cameraman.tif' into 8x8 blocks then run dct2 on each block to
later hide a binary watermark image into each block.
So far I tried blockproc and many other methods but none of them satisfy my needs.
2 Comments
dharaneesh govindaraj
on 23 Oct 2021
I want to do same process. I dont know how to convert the image and watermark. Please help me by providing code
Image Analyst
on 23 Oct 2021
Edited: Image Analyst
on 23 Oct 2021
@dharaneesh govindaraj, start with running and understanding my attached blockproc() demos. Then adapt them to make the function it runs fft2() instead of whatever I used. But this is essentially what Stephane does below.
Accepted Answer
Stephane Dauvillier
on 29 Apr 2019
Edited: Stephane Dauvillier
on 29 Apr 2019
file = 'cameraman.tif';
im=imread(file);
imshow(im);
In order to use blockproc you have to use a function that accpts blocksstructure, that's why you need to use something like this
imModified = blockproc(im,[8 8],@(blkStruct) dct2(blkStruct.data));
imshow(imModified)
I hope this answers your question
2 Comments
Stephane Dauvillier
on 29 Apr 2019
You have a function to add your watermak ?
Let's just say you have your function has followed
function imageWithWatermak = myFunction(imageWithoutWatermark)
...
end
Then you will do
blockproc(im,[8 8],@(blkStruct) myFunction(blkStruct.data));
More Answers (1)
KALYAN ACHARJYA
on 29 Apr 2019
Edited: KALYAN ACHARJYA
on 29 Apr 2019
image1=rgb2gray(imread('test.jpg'));
[rows colm]=size(image1);
% pading for make 8 disible, im my case rows 96 and colm 200
% 96 alread divisible by 8, no need modification: 12
% colm 200 no need modification: 25
% Otherwise do zero pading, where required rows or colm, or both
result=dct2(image1,[12 25]);
% This size [12 25] divides the image in 8x8 blocks, each block size is 12x25
imshow(result);
![77.png](https://www.mathworks.com/matlabcentral/answers/uploaded_files/217166/77.png)
There may more simpler way also.
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