matlab - Which kernel produces sharper image -

-

kernel = 

[ 0 -1 0
 -1 4 -1 
  0 -1 0 ]
and b = 
[-1 0 -1
  0 4 0
 -1 0 -1 ]

i have found frequency spectrums freqz2 function of matlab.

a's spectrum has highest magnitudes in corners [(1,1),(-1,-1),(1,-1),(-1,1) , b's in (1,0),(0,1),(-1,0),(0,-1).

i know center of frequency spectrum has low frequency information , corners high frequency information such edges. appears b filter produces sharper image although has higher magnitude in corners. why happening ?

from definitions can seen a tends sharpen more along vertical , horizontal directions, whereas b sharpens more along diagonals. depending on contents of image, 1 effect may more noticeable other.

in frequency terms, if kernel amplifies spatial frequencies @ image happens not have energy, effect hardly noticeable.


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