1,]) 
1,]) 
ip 
  
     
i 
1 
| 
i 
\ 
ih. 
Fig. 5 The result of C,G,j) transform for I(i,j) 
  
Fig. 6 The result of PCi,j) for ICi,j) 
bor pixels are white pixels, then trun it into a 
white pixel. We signed a shrinking transform as S 
(,)). Generally speaking, the lines in map images 
are more than one pixel in width because of the 
scanning resolution. Therefore, P (i,j) should be 
‚performed n times of shrinking transforms S, (i,j) 
in order to delete other graphics. The result of S, 
(i,j). (n=3) for P(i,j) is shown in Figure 7. 
4 
eg 
^ 73 
é ar 
2 x A 
Fig. 7. The result of S,(,j) (n=3) for PG,j) | 
4. SERIES EXPANSION TRANSFORMS 
The image S, (i,j) consists of only the shrinked 
black blocks. To restore the original shapes and 
sizes of these black bolcks, series expansion trans- 
forms should be performed to image S, (i,j). Ex- 
pansion transform is defined as follows: For a 
black pixel, let all of its neighbour white pixels be 
black pixels. Expansion transform is signed as E 
(i, j). For the same reason as series shrinking 
transforms, S,(i,j) should be performed n times 
expansion transforms E,(i,j) in order to restore 
the original shapes and sizes of the black blocks as 
in image P(i,j). The result of E,(i,j) (n— 3) for 
image S, (i,j) is shown in‘ Figure 8. The black 
blocks in image E, (i, j) represent some other 
graphics such as Chinese characters, small closed 
graphics and lines near the residential sections be- 
sides the hatched polygons. A new image Q (i,j) 
can be obtained from 
Qt, j) = (S, N DG,j) 
where IC(i,j) refers to the original image. The re- 
sult of Q(i,j) is shown in Figure 9. 
Fig. 8 The result of E.(G,j)(n=23) for S.G,}) 
f" 
€ da 
at sella ses caliney, € o" 
NN “lf m 
> 
2 T $2994 
» 
4 
Rs 
Fig. 9 The result of QCi,j) 
5. THINNING AND OPEN GRAPHICS DELETION 
Although there are fewer graphics in image Q (i,j) 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996