The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B7. Beijing 2008
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»©■«Kl)
where p is correlation coefficient.
Fig.l illustrates the process of traditional histogram matching.
Let vector ^ be the PAN image, vector be the low
resolution I component, then o? is the image retrieved from
Figure 2: Improved Histogram Matching Process
Based on Fig.2, the improved histogram matching process is
PAN following (1), where
|Ö?| = |ö?| and ¿7
is the
spatial detail provided by PAN image.
¿-(/•AN-,!«*>-
07
& FÀPtPlJPM
Pf
(5)
Figure 1: Traditional Histogram Matching Process
From Fig.l it is easy to find out that the angle between
and is greater than y. From (4) it is known that spatial
detail retrieved by this way must have negative correlation with
I component. In other words, more detail would be injected to
the part with low intensity, and less detail would be injected to
the part with high intensity. Such result is not so reasonable,
which might lead to spectral distortion and suppression of
spatial detail. Moreover, weak correlation between PAN and I,
which means a bigger Zf*OS , would aggravate the problem.
where Pgpju» ' s correlation coefficient between I and PAN
image.
3. DATA AND RESULTS
The method was tested for IKONOS II image of Beijing, China,
dated of 06/28/2002. Spatial resolution is 4m for MS and lm
for PAN. To validate the fusion result, MS and PAN image are
degraded to 16m and 4m respectively, and image fusion is
implemented on the degraded image to take the original MS
image as (Wald, L.,1999). IHS cylinder model (Zhou, J., et
al., 1998) is employed, transform and inverse transform is
shown in (6) and (7).
tt = ardartf—), S = y** 2 +1^ 1
Hence, the paper proposes a new histogram matching method to
avoid the problem and improve IHS method in spectral fidelity.
To avoid the problem raised above, it is intuitive to take
g* jaJjLtT? as constat to the histogram matching process.
Fig.2 illustrates the process. By this way, spatial detail
extracted must be orthogonal to I component, and has a positive
correlation with PAN image. Moreover, H is larger in
Fig.2 than in Fig.l, which means stronger spatial detail and
would lead to sharper fusion result.
R
if
—
P
l
f
is
1 -I
J
H
■
i
n
B
0
»
1*2 =
5 ■ slm/f )
(7)
To validate the influence of (5) on IHS method, traditional IHS
method using (1) is also applied on the degraded data to
compare with the proposed method. Test data and fusion result
is shown in Fig.III.