Herbert Jahn 
  
Figures 7 and 8 are zoomed versions of the sampled blurred test image in order to see better. What we see is that 
aliasing takes place in the striped pattern of the non-staggered sensor (fig. 7): wrong wavelength and wave direction are 
observed.The crossed line pairs and the dots can be resolved with the staggered array but not (or worse) with the non- 
staggered array. This demonstrates the superiority of the staggered array over the non-staggered CCD line. Other 
simulated images confirm that. 
   
       
    
Figure 7. Sampled test image, non-staggered Figure 8. Sampled test image, staggered 
4.2 Laboratory test 
To demonstrate the staggering effect once more, an experimental setup with a CCD camera was made. The aim of this 
experiment was to show the resolution enhancement of the staggering effect by subsampling an image by half of a pixel 
in horizontal and vertical direction. The target structure was a bar pattern with variable number of bars per mm. 
To show the resolution improvement using staggered arrays, the frequency of band limitation of the optics must be 
much bigger than the Nyquist frequency of the CCD-sensor. As a result, aliasing effects occur if target structures, which 
pass the optics, contain higher frequencies than the Nyquist limit. 
To show the resolution of the (non-staggered) camera the optics was defocused in order to avoid aliasing The bar 
pattern consists of strips from 1 lp/mm to 10 Ip/mm (which is seen left and right of the bar pattern). With respect to the 
magnification of this optical arrangement of about 6 the frequency spectrum in front of the CCD-matrix is between 6 
and 60 Ip/mm. 
  
    
  
VORB i 
Figu e 9. Original defocused non-staggered image Figure 10. Original focused non-staggered image 
Figure 9 shows, that the bar patterns are resolvable in vertical direction up to about 4 Ip/mm. Taking into account the 
magnification this corresponds to about 25lp/mm and is in consistence with the pixel pitch of 20 um. The difference to 
the non defocused sharpest possible image is shown in figure 10. The aliasing effects (here especially as Moire patterns 
and frequency changes) are obvious. 
To simulate a staggered array (i.e. to apply subsampling), the CCD matrix was shifted in horizontal and vertical 
direction by half of a pixel. After measuring, the four generated images have been rearranged in a twice bigger image. 
  
170 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B1. Amsterdam 2000. 
  
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