International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B3. Istanbul 2004
achieve a good estimate of both. The CMOS image of such a pop MR TY
target is shown in Figure 4. an
T
Figure 8. Fitting a rectangle on Wiener profile
Now, by fitting a proper 1-D Gaussian to the PSF profile, the
Figure 4. Digital CMOS image of an ideal target oscillations of PSF will be reduced. The total PSF of the system
will be achieved by expanding the 1-D Gaussian function to the
The second step is to select a patch of one of the individual 2-D Gaussian function:
targets (rectangles), that includes two vertical edges (Figure 5). RR QUE gare
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=
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2
| Profile
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Pall,
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0 Bo
dle), fitted
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Figure 9. PSF profi ), Gaussian function (mid
Gaussian function to PSF profile (right).
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Figure 5. One of the edge targets (left) and corresponding
picked up patch 2.4 The Wiener Deconvolution Filter
The third step is to reduce the noise in the above selected image By using the calculated PSF and noise to signal power ratio (K),
patch by applying a low-pass filter, for example an averaging the Wiener deconvolution filter can be calculated by using
filter with a 5x5 window (Figure 6). Equation 4. The size of this filter should be expanded to the size
of the image patch, which is to be restored (Stockam, et. al,
AA 1975).
+10 ;
on [3 2.5 Experiments and Results
a J 1d
@ | | : :
m f^ To evaluate the proposed restoration process, the estimated PSF
2e — is used for radiometric correction of an outdoor image (Figure
Figure 6. Image (left) and signal (the data without noise) 10). Visual comparison of the obtained result with the input
profiles (right). image demonstrates the capability of the applied restoration
strategy.
By subtracting the result of averaging filter from its
corresponding image patch, the noise profile is achieved, as
shown in Figure 7:
SOE Noe pee EN
| Subtracting NIE: V A
Signal 38 | |
| Averaging 3 \ |
EIE IAS eh 80
Figure 7. Left: Signal profile (result of lowpass filter), Right:
Noise profile.
Now, a Wiener filter should be applied to the image patch to a
create a profile, which just contains the system blur effect. By
fitting a rectangle (Figure 8), which indicates the ideal signal
profile, on the profile of Wiener filter, the PSF of the CMOS
system can be calculated in frequency domain by the
expression:
H LISD)
Where H(orr,is OTF (Fourier transform of the 1-D PSF),
(5)
FT(SP)is Fourier transform of the signal profile and FES Sol cra
FT(RP) is Fourier transform of the rectangle profile. Figure 10. Initial image (above) and the restored image
generated by Wiener deconvolution (below).
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