The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B7. Beijing 2008 
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The main weakness of ratio image is lost the reflection 
intensity information of ground objects. In order to remedy the 
deficiency, one origin band and two ratio images can be 
combined into one color image[3]. 
In this paper, the method of combining two ratio images with 
one original band is researched. Because this method reserve 
not only absolute radiometric information which have missed 
in ratio images, but also some terrain detail information which 
can distinguish some objects on the ground. It is easier for 
people to interpretation. 
Figure.2 False Color Image 
Figure 2 is a hybrid false color image . In the image ,the Red 
band is the ratio of band five and band one ,and the Green band 
is original band one ,and the Blue band is the ratio of band five 
and band one . The image is combinated by two ratio images 
and one original band together which show us a better effect 
one . Not only can it show us some important things on the 
ground, but also some details of terrain. The effect is better 
than that of tradition method dealing with in specialty fields 
such as mineral. 
However, this method still has some disadvantages^]. 
Abnormal of tonality will cause some difference of color in the 
image. In RGB color system, color is defined by the proportion 
of tricolor. The change of each one of tricolor will cause that of 
color characteristic. The color can hardly described by number 
well and truly. And the levels of number can hardly expressed 
by a certain color, too. 
4. THE OPTIMUM INDEX FACTOR(OIF) METHOD 
Because the combination of R,G,B band is really complex and 
changeable, the final result of image is different. In some cases, 
it is difficult to choose a appropriate combination scheme for 
false color composite of ratio images or select a color to 
describe the specific information. 
How to select the most useful combination achieving the best 
reinforcing effect? Nowadays two methods have been 
adopted[5]. First is to select the most suitable bands which can 
identify different geologic body. The other is to select the 
bands depended on statistical characteristics of images. 
4.1 the Formula of OIF Method 
In this paper, through researching the effect of ratio false color 
composite image of RS images, the method of OIF (The 
Optimum Index Factor) is discussed. Chavez ec al. has been 
put forward a formula to calculate OIF(The Optimum Index 
Factor) by using three standard deviation and correlation 
coefficient. 
OIF = Y d SDi/jfCC]\ 
i=1 J=l (1) 
In the formula (1), SDi means the standard deviation. |CCi| 
means the absolute value of correlation coefficient. Standard 
deviation represents the discrete degree. The more value it will 
be ,the more radiation intensity difference we can see. And the 
less of the |CCi| ,the less of repeated degree . 
The bigger OIF value we have calculated, the more information 
the color image contains. And the less redundancy information 
it is. So it is easy to understand that the biggest OIF value 
represents the prime combination. 
4.2 the Disadvantages of OIF Method 
In the paper, in order to find a suitable combination scheme, the 
OIF method is used to evaluating them objectively. Although 
the method of OIF value is effective on representing the display 
effect and narrowing the possible wave bands combination, the 
disadvantages are very obvious[6,7]. 
(1) The OIF value embodies that of image information entropy 
of from one side and there is no necessary association between 
the value of OIF and image quality evaluation. 
(2) Some images with similar bands combination have similar 
OIF value, unfortunately their display effects are dissimilar 
obviously. 
(3) The best image combination maybe not just the image of 
the analyst wanted with special information. 
5. RELATIONSHIP BETWEEN THE OIF VALUE AND 
THE SCALES OF THE WINDOW 
First two ratio image we talked above are filtered by sliding 
window method with different scales. Then two new 
characteristic matrix we have got are synthesized into a false 
color image with a original band. Finally we calculate the 
OIF value. 
For the sake of discussion, a simple expression is provided. 
R=band51 mean a new characteristic matrix which can be got 
by filtered with different scales of window after band one 
divided by band five . The scales of filter window are set in 
different sizes. Such as ^ x 3 ^ 5x5^ 7 X 7 ^ 9x9 
11x11 13x13 15x15 17x17 19x19^ 
21x21, 31x31^ 41x41 Based on the formula of OIF, 
the OIF value is closely related not only the scale of sliding 
window but also the choice of original band [8,9]. 
Research area of RS image is Tieshan mining area in Daye city , 
Hubei province. Because it is a big opencast mine area where 
the research data is relatively comprehensive. And the 
prospecting criteria alteration zones can be found easily 
which will affect some RS bands a lot. So the OIF value is