4.2.6 On-line Help System. In order to help the 
users, who do not understand the characteristcs and 
performance of EM3DPS very well, to learn how to 
operate the system quickly, EM3DPS provides an on- 
line help system. When the operator chooses HELP in 
the main menu, the system comes into on line help 
status. At this time, the structure of the menu 
displayed on the screen is the same as before, but the 
color of the menu has been changed. This indicates 
that the system is in on line help status. Now, after 
a system function has been chosen, some related help 
information will be displayed on the screen instead of 
performing the function. The help information has 
been written in two languages: English and Chinese. 
5. SOME KEY TECHNIQUES 
For developing an electron microscope digital image 3D 
processing system on a microcomputer, we must take 
account of some limitations of the microcomputer such 
as speed, memory space and the color number of the 
graphic card, and then use some techniques and 
methods to bring into full play the potentials of the 
microcomputer. 
5.1 SPEED CONSIDERATIONS 
The speed of displaying and operating images is one 
of the key problems in developing EM digital image 
3D processing system on a microcomputer. The pulse 
frequancy of the microcomputer is definite, so the 
efficiency of programming affect the speed of 
displaying and operating images directly. The system 
chooses efficient C language as the main language and 
displays images by reading and writting the video 
memory directly. On the microcomputer without 
special image card, it is impossible for the two images 
of a stereopair to realize image roam at the same 
time. In order to observe all parts of the left and the 
right images through half of the screen, a so-called 
virtual roam has been used inEM3DPS. When the 
cursor approaches the edge of the image, new image 
data are automatically transmitted into the video 
memory from the disk. If the microcomputer is 
equiped with extend memory, it is suggested to build 
a virtual disk in the extend memory and store the 
EM images on it. The reason why the extend 
memory should be used by way of virtual disk is that 
this makes the EM3DPS more flexible, since the 
operation procedures of a physical disk and a virtual 
disk are the same. 
To a single 1024 X 512 16 grey level EM image, VGA 
provides roam function in mode 12H (640 X 480 16 
color). By means of the offset register in CRT 
control registers, a logical screen wider than the 
physical screen can be built. To display the image 
which is in the logical screen but not in the physical 
screen, the only thing to do is to update the 
startaddress register of the video memory. 
5.2 MEMORY CONSIDERATIONS 
Although EM images are not as large as aerial digital 
images, the problem of how to use the limited (640 
KM in PC DOS or MS DOS) memory space in a 
microcomputer should also be considered in 
programming. The author has used different tactics to 
take advantage of the memory space for running the 
program and storing the image data. 
5.2.1 Space For Running The Program. The total 
EM3DPS consists of about ten thousand of C 
original codes. In order to economize the memory 
space occupied by C original codes, the overlay 
technique has been used. As the size of data segment 
and code segment all exceed 64KB, the large mode is 
required in compiling and linking. 
5.2.2 Space For Storing Image Data. VGA can 
only provides two types of grey level( 16 and 64) 
to display white and black images. Since each pixel 
value only requires half byte to 16 grey level image, 
two pixel values can be compressed into one byte. 
This can economize half of the data space. This kind 
of image data file compressing can be performed in 
TRANSFORM of the system. 
5.3 COLOR CONSIDERATIONS 
Another limitation for developing EM digital image 3D 
processing system on a microcomputer is the color 
number. VGA can only display 16 colors in the highest 
resolution mode (640 X 480) at the same time. This 
mode can only be used to display 16 grey level white 
and black or false color images.In order to display 64 
grey level images and realize images superimposition (or 
graphic and image superimposition), we must use 
mode 13H (320 X 200 256 color). In mode 13H, it is 
possible to perform two 16 grey level images 
superimposition or a few graphics and a 64 grey level 
image superimposition. 
6. CONCLUSIONS 
(1) At present, various powerful special computers 
for image processing and machine vision are emerging 
continuously. When these hardware systems are used, 
a better and more efficient electron microscope digital 
image 3D processing system can certainly be 
developed. Yet, as these kinds of systems are quite 
complex and costly, they are not readily accessible to 
general electron microscope users. On the contrary, 
the system described in this paper may be more 
acceptable, since the system meets the desirable 
requirements of flexibility, simplicity and adaptability. 
(2) EM3DPS can complete various surveying tasks 
that can be done on conventional stereoplotters, 
      
  
   
  
  
  
   
  
  
  
  
  
  
  
  
   
  
  
   
    
   
  
  
  
   
  
   
  
   
    
   
  
   
   
  
  
  
   
  
   
   
  
  
  
  
  
   
  
   
  
  
  
  
  
    
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