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Why do i get different results when i perform convolution with different ways?

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Gn Gnk 2020-12-10

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https://ww2.mathworks.cn/matlabcentral/answers/689644-why-do-i-get-different-results-when-i-perform-convolution-with-different-ways

评论： Gn Gnk 2020-12-10

采纳的回答： Matt J

Hello ,

i have an image 30x30 and i want to perform convolution with a filter 9x9 using 2 methods . Firstly , i need to perform the convolution using conv2() and then using ifft2(fft2(image)*fft2(filter)) . Can someone explain why in the first case i get back a 38x38 result as expected ( i am aware that the result after the convolution is length(image+filter-1)) but in the second i get back a 30x30 result? Isn't supposed to be the same procedure ?

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Matt J 2020-12-10

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编辑：Matt J 2020-12-10

No, it's not the same procedure. conv2 performs linear convolution, wherease your fft method performs cyclic convolution. See also,

https://www.mathworks.com/help/signal/ug/linear-and-circular-convolution.html

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Matt J 2020-12-10

The link I gave you discusses how to compare them.

Gn Gnk 2020-12-10

Thank you a lot ,it really helped me !

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