The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B7. Beijing 2008
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c) Traditional IHS Result d) Improved IHS Result
Figure 3: Image Fusion Result
a) Original MS 4m
b) Degraded MS 16m
VALIDATION AND DISCUSSION
3.1 Visual Comparison
Comparing Fig.3(d) and Fig.3(c) with Fig.3(a), it is found that
result retrieved from traditional method is a little too blue and
grey, while the proposed method is closer to the reference
image in tone.
UIQI is a comprehensive image quality index (Wang, Z., et
al. ,2002), which has been used to measure the similarity
between two images. UIQI is defined as (10) and the result is
shown in Table 3.
Vjm 2g-,4 o-g
WA<r B
Band
Origin
IHS
Proposed Method
1
10.1021
13.1679
14.9425
2
17.6524
14.5899
16.3799
3
23.0011
15.8605
17.6275
4
30.8366
17.1412
18.8309
Table 1: Average Gradient of Reference and the Two Fused
Images
Band
IHS
Proposed Method
1
0.024133
0.024763
2
0.0256
0.024226
3
0.03775
0.034866
4
0.042655
0.039324
Table 2: Relative Difference between Reference and the Two
Fused Images
3.2 Quantitative Assessment
Three image indexes is used to assess the fusion result
compared to original MS image. Average gradient (AG) assess
sharpness of image, which is calculated by (8) and the
assessment is shown in Table 1.
m ff jl i' flsfra&h
1 y yd* *■» ' »
where M, N is column and row number of the image Z.
Relative difference (RD) is an index to assess the distortion of
fused image compared with reference image. RD is calculated
by (9) and the result is shown in Table 2.
Band
IHS
Proposed Method
1
0.827015
0.84231
2
0.92246
0.93537
3
0.936051
0.947459
4
0.91383
0.926604
Table 3: UIQI between Reference and the Two Fused Images
Table 1 shows that the fusion result retrieved from the proposed
method is sharper than traditional method in every band and is
closer to the reference image except band 1. Such result is
expected because the improved histogram matching method
extract more spatial detail. Table 2 shows that the proposed
method lead to less RD than traditional method in every band,
which means less spectral distortion is introduced by employing
the improved histogram matching method. Table 3 shows that
the proposed method produces fusion image with higher UIQI
than traditional IHS method, which is caused by higher
sharpness and lower spectral distortion.
t r* v 1
where A and F are reference image and fused image
respectively.
4. CONCLUSION
The paper proposed an improved IHS image fusion method by
proposing a new histogram matching method. Histogram
matching process is analyzed and improved by introducing an
image vector space. The fusion result of the proposed method is
satisfactory. As histogram matching is a necessary step for most
image fusion methods, the proposed histogram matching
method could be applied to improve those methods.