and not to increase as far as the number of clusters does 
not increase even if the classified area of MSS data 
increases. The histogram table is desired to be constructed 
as skilful as it has to be accessed at minimum time and it 
can be effectively utilized because it is accessed as same 
times as the number of pixels in the imageries. 
Generation of MDH table 
Indexed link structured table. We authors considered 
that the indexed link structure as shown in Fig.1 is best 
for realizing the shortest access time and the high 
performance for memory usage. The index has 1024 entries in 
the figure. Ten bits key are obtained by concatinating 
lower five bits of one channel data with lower five bits of 
another channel data are used for accessing the index table. 
The contents in the index indicates the adress of the 
histogram cell corresponding to the data pixel. 
MDH table 
Fig . 1 
Multi-dimensional 
histogram 
A histogram cell contains pixel data , frequency,c1uster 
number and pointer. Its length is sixteen bytes. In 
general.it can be easily found there is not only one pixcel 
whose data have the key of the equal value. 
Access time. They are linked by the pointer which shows 
the address of the other cells with the key of the same 
value. Mean access time T is represented by followings; 
T = To 
T1 1023 j nk 
# Z * Z * j * Z fki 
N k = 0 j = 1 i = 1 
(4 ) 
312