Full text: Actes du Symposium International de la Commission VII de la Société Internationale de Photogrammétrie et Télédétection (Volume 1)

  
  
n-1 M-1 -2ni (ot +) 
F(u,v) = NEN X ^  s(n,mje (5) 
n=0 m=0 
with u and v the discrete frequencies in x and y-direction and n,m the image coordi- 
nates of pixel s(n,m) (KOLOUCH et al. 1981). 
Fig.4 shows the original image with its logarithmic power spectrum in fig.5. 
  
  
Fig. 4: Original scene Fig. 5: Power spectrum and filter design 
There are no characteristic maxima on the v-axis which point to a narrow-band scan- 
line noise. 
One can find a relative uniform distribution of the noise over the whole frequency 
axis. Therefore a seperation of noise and signal is very difficult. The same effect 
is shown by the one-dimensional power spectrum of an image column in fig.6. Instead 
of an intensity decrease with higher frequencies there is a plateau-like behaviour. 
Frequency domain filter design and realization 
For the estimation of those parts of the power spectrum which have to be filtered 
channel 9 (A = 810 * 50 um) with nearly no noise, is transformed into frequency do- 
main. Fig.7 shows the v-frequency axis of thermal channel 11 (A = 10 * 2 um) and 
channel 9. 
For detection of scan-line noise in the thermal channel formula (6) is used. 
|F41(0,v)|. 7 |Fg(0,v)| 1 (6) 
F,, and F, are the normalized spectra of channel 11 and 9 of the scanner imagery 
rédpectivdly. The lower part of fig.7 contents the log. ratio of both. There is a 
strong increase of intensity with increasing frequency. Formula (6) is nearly ful- 
filled for all frequencies Fr ~ 0.2 Fy with Fy as Nyquist-frequency according to the 
sampling theorem. 
Using this analysis a narrow-band two-dimensional filter-transfer-function H(u,v) 
around the v-axis is designed with smoothed corners by a sinusoidale mask to avoid 
oscillation while filtering (SFB 149, 1981). Fig.5 shows the filter-position in the 
138 
ERE SACRA ULE re a a 5 50 rm d n 
mu a amar ES - ^ 
P 3 = Ex E 
freque 
ing th 
The hi 
relati 
anothe 
Fig. 6 
Fig. 7. 
For th 
sider ; 
by the 
(n, 
This c. 
compar 
It can 
higher 
Using 
number
	        
Waiting...

Note to user

Dear user,

In response to current developments in the web technology used by the Goobi viewer, the software no longer supports your browser.

Please use one of the following browsers to display this page correctly.

Thank you.