Exercise session 5 - Exercise 3 : Image sharpening : kronecker

Exercise session 5 - Exercise 3 : Image sharpening : kronecker

by Younes Moussaif -
Number of replies: 1

Hello, 

In the 3rd exercise it was mentioned that : 

"Then, the sharpening filter is defined as \delta - L, where \delta is a 3\times3 Kronecker delta kernel with a values of 1 at the diagonal elements and zero elsewhere" 

I expected delta to be the Identity matrix, but in the correction it is instead the matrix [[1,0,0], [0,0,0],[0,0,0]], using the same matrix as in the correction yields better results and I was wondering whether it was a choice to improve the results  or is the matrix just meant to be [[1,0,0], [0,0,0],[0,0,0]]? (using an identity matrix gives a less clear image)

Thank you for your time
In reply to Younes Moussaif

Re: Exercise session 5 - Exercise 3 : Image sharpening : kronecker

by Andrey Davydov -

Thanks for a catch!

Indeed, solutions have a little bug, "kronecker" is supposed to be identity matrix, while in the solutions only one diagonal element is 1 and the rest are all 0. It can be seen as I - L, where L is not correct sharpening but some weird filter. It is hard to figure out what exactly this filter is doing: you can see those -1 as the noise added to your filter.

If you correct the mistake and subtract L from identity, then result would be much sharper, better highlighting the desired object. 


Here is a screenshot with comparison for you: top - wrong filter, bottom - correct filter

sharpening