the CCD 
he true-to- 
ay lead to 
tical work 
Klaus J. Neumann 
3 NOISE BEHAVIOR AND INFLUENCE OF INTEGRATION TIME AND ILLUMINATION 
To investigate the noise behavior, several homogeneous gray glass plates with different optical densities were scanned. 
The advantage of glass-based over film-based gray scales lies in the absence of noise caused by the granular film 
structure, thus permitting the actual signal noise to be measured. An alternative approach would be the scanning of a 
film-based gray scale outside the region of focus, which would also eliminate noise caused by film granularity. All tests 
were with 7 um scans. To establish the influence of illumination on the noise behavior, different types of light source 
were used. The computation was based on an area of 4.4 million pixels per glass plate. 
Fig. 5 shows the standard deviation of the color channels for a plate with a density of 0.31 and varying integration time. 
The noise is most pronounced in the blue channel and increases almost linearly with higher integration time. 
33221(D=0,3171) 
  
  
  
  
  
  
mem SED. RED 
#- St. D. GREEN 
—# St.D. BLUE 
  
grey value 
  
  
  
  
  
  
  
  
exposure time [ms] 
Figure 5. Noise of the sensor as function of integration time, 150 Watt Halogen lamp. 
A 250 W halogen lamp was used for the next test. The results show that the noise is reduced as the illumination 
intensity increases. An explanation for this effect is that the gain values needed for the CCD camera adjustment are 
lower. The noise can be also reduced by converging the light through a collector lens, which leads also to a lower gain 
for the analog amplifiers on the CCD camera board. 
A difference is noticeable between the individual color channels in Figures 5 and 6, with the noise being most 
pronounced in the blue channel and virtually identical in the green and red channels. This effect is also attributable to 
the spectral characteristics of the CCD elements — the blue channel displays the lowest sensitivity — and to the spectral 
properties of the light source. To decrease this effect, Kodak has developed CCD sensors with an enhanced responsivity 
called enhanced CFA (Eastman Kodak, 1998). 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part Bl. Amsterdam 2000. 217