The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B7. Beijing 2008 
1254 
»©■«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.