Fundus Camera 
Film 
Surface 
Photographing 
Relay Lenses 
  
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Ss 
od 
— 
e 
oo 
c 
o 
sd 
  
Fig - 4 Optical concept on photogrammetry 
4. Processing flow 
Processing flow of the system for 
the ocular fundus DEM and diagnostic 
analysis is as fig - 5. 
1) Extraction 
Stereo ocular fundus images are 
taken in one file according to the fundus 
camera structure. Therefore, those images 
have to extract in each file to be obeyed 
photogrammetric order. 
One bit image is made from the 
original image, and noises in the image is 
removed. Next, according to method of least 
squares, the solution of a linear equation of 
four side lines of fundus image is calculated. 
From those result of correlation coefficients, 
one of four side lines that have most high 
straightness is used as basis of extraction. 
Then, according to the scale of image frame 
in the fundus camera, stereo images are 
extracted to each files (fig - 6). 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
3 4 
Fig-6 Extraction 
2) Interpolation 
Image data getting form CCD 
camera is not fine enough pixel size for 
measuring accurately. So that cubic 
convolution is incorporated, and the 
resolution of height is enlarged (fig - 14). 
560 
3) Orientation 
It is impossible to make control 
points on ocular fundus surfaces. Also it is 
very hard to makes fundus model with 
control points. So that we used nominal 
values of the fundus camera as the 
orientation factors (fig - 7). 
4) Datum plane 
A spatial image moves to front or 
back depend on  shortsightedness or 
longsightedness. According to this 
phenomenon, a stereo fundus image move to 
inside or outside on the film. On this length 
of shift value, basis of height become a unique 
on each ocular fundus. So that to make 
standard level of height, the slide difference 
is modified according to extracted distinctive 
features. 
Relation of spatial image movement 
by shortsightedness and longsightedness are 
as fig - 8 and fig - 9. 
Fig-8 Shortsightedness 
OH EG 
Fig -9 Longsightedness 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
The shift value of entire up/down 
for vertical parallax and left/right for 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B5. Vienna 1996