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Thread Subject:
convolution vs correlation

Subject: convolution vs correlation

From: Sadiah Jantan

Date: 13 Jul, 2011 04:08:10

Message: 1 of 3

In convolution, do the kernel need to be rotated 180 degrees each time. What is the main purpose, and what is the difference in terms of purpose and output as compared to the correlation.

Subject: convolution vs correlation

From: Yumnam Kirani

Date: 13 Jul, 2011 08:16:10

Message: 2 of 3

"Sadiah Jantan" wrote in message <ivj5na$30p$1@newscl01ah.mathworks.com>...
> In convolution, do the kernel need to be rotated 180 degrees each time. What is the main purpose, and what is the difference in terms of purpose and output as compared to the correlation.

suppose, you have two numbers 1 1 2 and 1 2 2, then convoloution of [1 1 2] and [1 2 2] gives you multiplication of 112 and 122, i.e., 1 3 6 6 4, but you find the correlation between [1 1 2] and [ 1 2 2], you will get the multiplication of 112 and 221, i.e., 2 4 7 5 2.
Convolution is most often used for filtering operation, where correlation is usually used for testing of similarity between two signals. But both can be used interchangeably.

Yumnam Kirani Singh
Tronglaobi Awang Leikai

Subject: convolution vs correlation

From: Florin Neacsu

Date: 13 Jul, 2011 18:52:28

Message: 3 of 3

"Yumnam Kirani" <kirani.singh@gmail.com> wrote in message <ivjk8a$7mg$1@newscl01ah.mathworks.com>...
> "Sadiah Jantan" wrote in message <ivj5na$30p$1@newscl01ah.mathworks.com>...
> > In convolution, do the kernel need to be rotated 180 degrees each time. What is the main purpose, and what is the difference in terms of purpose and output as compared to the correlation.
>
> suppose, you have two numbers 1 1 2 and 1 2 2, then convoloution of [1 1 2] and [1 2 2] gives you multiplication of 112 and 122, i.e., 1 3 6 6 4, but you find the correlation between [1 1 2] and [ 1 2 2], you will get the multiplication of 112 and 221, i.e., 2 4 7 5 2.
> Convolution is most often used for filtering operation, where correlation is usually used for testing of similarity between two signals. But both can be used interchangeably.
>
> Yumnam Kirani Singh
> Tronglaobi Awang Leikai

Hello,

I have to disagree with you again.

>But both can be used interchangeably.

Not quite. Depends on the domain and the functions. In order to have interchangeability one of the functions must be Hermitian.

Regards,
Florin

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