SR SE NE 
AS AS À 
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Figure 4: Siemens star with 32 wedges: For smaller radii 
the spatial frequency of concentric circles is increasing. 
The smallest radius where all wedges are resolved char- 
acterizes the quality of the image. 
  
  
  
  
  
  
of the test images, 
G—1 
H,=— M P(k)log2[P(k)] 
k 
iz 
for an image with G gray-levels and the probability of 
gray-level k is P(k). For an ideal homogenous patch con- 
taining only one gray-level the entropy is 0. Smaller en- 
tropy indicates less information content and is a measure 
for image noise, if calculated in a homogenous patch. 
3 RESULTS 
All testing methods were performed on all film images 
scanned with 5, 10, 15 and 20pm and on the ccd images 
with 9m which covers the same area as the 20m scans. 
If we have an ideal film image and an ideal scanner we 
could scan the image with e.g. double resolution and will 
get the same results for e.g. the Siemens star test. As we 
are dealing with real film images it is obvious that the geo- 
metric performance will not stay the same when scanning 
with very high resolution, because the granularity of the 
film causes image noise. 
In the following tables the values in brackets are the ra- 
tios to the 51m scans. If the ratio is higher than the ratio 
between the resolutions (i.e. between Hum and 15m we 
have ratio of 3), this indicates that there is no more infor- 
mation in the 5pm image than in the lower resolution one. 
So if the ratio is about 2.0 for the 10m, 3.0 for the 15um 
and 4.0 for the 20pm scan, then we know that the 20pm 
scan contains same geometric accuracy as the Sum and 
therefore scanning with 20m makes sense without losing 
information. 
For ideal images the ratio is 1.0 independent of the resolu- 
tion. 
3.1 Image matching 
For the image matching setup we used stereo images with 
a baseline of about 10 meters. One of the stereo images 
is shown in figure 5. Then 10000 points of interest were 
extracted from the reference image and reallocated in the 
search image. Reference and search window size were 
adapted according to the scan size. For example if we have 
a search window size of 600 x 80 pixel in the Sum case, 
then the window size for the 20pm case is smaller by a 
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B3. Istanbul 2004 
factor of 4, so 150 x 20 pixels. This guarantees that these 
windows covers the same area in the real object. 
VE 
    
Figure 5: One image of the stereo scene taken with ccd 
sensor. Shown are 1800 x 1200 pixels. 
Figure 6 shows the histograms of the absolute distances to 
the epipolar lines for film delta scanned with 5, 10, 15 and 
20um. The histograms are scaled so that each histogram 
shows the same distances in object space (e.g. 8 pixels in 
Spm are 2 pixels in a 20pm scan). As quality measure we 
choose full width at half maximum, called c. The ratios of 
these c values are 2.06, 2.91 and 3.12 which means that 
the 15m scan leads to same accuracy as the 5um scan, 
but scanning with 20pm leads to a slight loss of quality. 
All results for this test are given in table 1. 
Figure 7 shows the histograms for 20m scans and for the 
ccd image. The number of matched points is significantly 
higher for ccd case and the o value of ccd outperforms the 
film with a factor of 2 to 3, which means on average 2.5 
times better image matching results. 
Table 2 shows the maximal absolute distance for the best 
1000 matches and here the accuracy in 20pm scan is even 
better than using the 5m scan. The digital ccd image out- 
performs the 20m scans by a factor of 3.0 to 5.0. 
  
1138 
  
  
  
  
  
  
oum 10um 151m 20pm 
apx 2.078 1.156 0s) | 0.724 ox» | 0.656 545 
delta | 2.000 | 0.969 coe) | 0.688 299 | 0.641 63.12) 
t-max 1.950 0.924 (2.11) 0.691 (282 0.453 (4.30) 
t-pan 1.989 1.042 non | 0.732 em | 0.453 (439) 
ced Yum - - - 0.219 
  
  
Table 1: Full width at half height of distances to the epipo- 
lar line in pixels (values in the brackets are the ratios to 
oum scan). 
  
  
  
  
  
  
  
oum 10pm 15um 201m 
apx 1.232 0.597 (2.06) 0.386 (3.19) 0.272 «s» 
delta | 1.080 | 0.397 2», | 0.288 «s» | 0.229 «m 
t-max 0.739 0.278 (2.66) 0.226 (3.14) 0.183 (4.04) 
t-pan 0.803 | 0.315 (ss, | 0.268 ov» | 0.171 am) 
ced 91m - - - 0.0557 
  
  
Table 2: Maximal distances to the epipolar of the 1000 
best matches in pixels (values in the brackets are the ratios 
to Sum scan). 
     
   
   
   
   
   
    
   
   
   
    
   
   
  
   
  
  
  
    
   
   
   
    
   
    
     
   
    
    
  
    
     
     
   
   
    
  
   
    
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