fourier 2

Question 1

sampling is equal to……….. with a periodic series of ………….

Answer 1

sampling is equal to multiplication with a periodic series of delta functions

Question 2

‘Ideal’ filters cause

Answer 2

overshoots!
=> need filter that is limited in both domains
Gaussian

Question 3

Homomorphic filtering

Answer 3

An image function is a product of an illumination function and a reflectance or transmittance function

The illumination function is assumed to vary slowlyàlow frequencies dominate
the reflectance function shows detailsàhigh frequencies dominate

Question 4

Methods to reduce the effect of intensity steps at the borders

Answer 4

mirrored version:
- still step in the first derivative of intensity
- symmetric = only cos-transform
- phase information lost
- orientation information lost
- about 2 times longer calculation

multiplied with
Hanning window or other windows:
- reduced information at the image borders =- smoothed frequency spectrum

Question 5

………. in one domain lead to ringing in the other

Answer 5

sharp cutoffs in one domain lead to ringing in the other

Question 6

edges can be detected by

Answer 6

edges can be detected by derivative operations