and fog density Do must be larger than some 
threshold, so that the image of low luminance 
subjective can be observed. From the above 
conclusions, the value 0. 07 is the contrast 
threshold AD in the bottom of low density, when 
Tab.2 The density range of each class 
  
excellent qualified 
unqualified 
  
No. D. D, Din Doux AD No. D. D, Din 
D, ‚AD No. | D, D, Dim Dux AD 
  
6 |0.59|1.31|0.68|/1.96|1.28| 1 /|0.93,1.50/1.03 
1.97|0.94| 2 |0.72|1.11|0.85|1.38|0.53 
  
9 |0.33|0.81/|0.41/1.35/0.94, 3 |0.91|1.59/0.98 
2.03|1.05| 4 /0.69:1.0410.76,1.31,0.56 
  
10 |0.43/0.97|0.52|1.58|1.06| 5 |0.82|1.65/0.91 
2.21|1.30| 7 |0.08/0.59/0.14|1.38/1.24 
  
11 |0.32/0.87|0.47|1.67|1.20| 15 |0.4110.86/0.50 
1.37/0.87| 8 |0.04:0.38/0.11|1.23/1.12 
  
12 |0.42/1.12/0.74/1.68/0.94| 17 |0.13/0.71/0.31 
1.24|0.93| 16 |0.05/0.4410.15/0.89|0.74 
  
13 |0.28/|0.83/|0.46/1.64|1.18| 18 |0.14/0.74/0.32 
1.31/0.99| 20 |0.16/0.74/0.26,1.19/0.93 
  
14 |0.29|0.99|0.40]1.68/1.28| 21 |0.52/1.07/0.65 
1.57\0.92| 30 |0.06{0.29|0.19|/0.71{0.52 
  
19 |0.20|0.88|0.32|1.64|1.32| 23 |0.75|1.19/0.93 
1.4410.51| 36 |0.07,0.33/0.22/0.80/0.58 
  
22 10.42|1.12|0.74|1.68|0.94| 27 |0.19{0.55|0.27 
1.1410.87| 37 10.0510.3110.2010.6210.42 
  
24 |0.69|1.01|0.80|1.55/0.75| 19 |0.11|0.47|0.24 
  
1.11/0.87| 38 |1.29|1.77|1.44{2.2110.77 
3 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
25 |0.44|0.91|0.50|1.25|0.75| 31 |0.95|1.45|1.08|1.98|0.90| 39 |0.94|1.55|1.09|2.18|1.09 
26 |0.22|1.00|0.29|1.65|1.36| 32 |1.03|1.48|1.16|1.85/0.69 
28 10.18/0.81|0.29|1.42|1.13| 33 |0.79|1.28/0.92|1.88/0.96 
34 |0.32/0.78|0.47|1.79|1.32 
35 10.370 86/0 5211.52 | 1.00 
min |0.18/|0.78/0.29|1.25/0.75| min |0.11/0.47/|0.24| L.11/0.51| min [0.04 0.6210.42 
max |0.69|1.31/0.80/1.96|1.36| max |1.03|1.65|1.16|2.21| 1.30! max11.28 2:24 
Din "D. 0.20 —0.45 Daun -Do: 0.15 - 0.90 Dyin — Do: <0.150r>0.90 
D, : 0.80 - 1.10 D.-- 0.60 — 1.30 D, «0.600r»1.50 
ord Dan. 0.35— 0 75 | ord Du: 030—100 lord Duin: <0.300r>1.00 
Du 140-170 BD... 130-2060 Dix *0.300122.00 
AD: 0.90 1.30 AD; 0.70 - 1.30 AD: <0.70or>1.30 
  
  
  
  
* D,=Dmin-Do; ord: ordinary case 
0. 07 times two is about 0. 15, so the lower limit 
of Dai, is about Do + 0. 15. Tab. 2 shows that 
the Duin of the excellent picture ranges from 
Do+0. 20 to Dot 0. 45, and the D, of the 
qualified one ranges from D, + 0. 1 5 to Dy + 0. 
90. The subjective in shadow and the details can 
not be reproduced when D,, is too small. And 
although the subjective of low luminance can be 
reproduced very well, but the image of high 
luminance subjective would be compressed 
when the Dy, is too large. The upper limit of 
Duin is controlled by both the contrast AD and 
the maximal density D,,,.. 
5.3 Maximal density Danax 
Dmax Should be in the top of the curve's linear 
section, but not in the shoulder. And it must not 
exceed the upper limit of density corresponding 
to 0.8Rmax From the above conclusions, the 
high image contrast is required when people 
recognize high density image, and the image 
contrast in shoulder is obviously less than others. 
So Dy. should not be too large. In Tab. 2 we 
can see that the D,,,, ranges from 1.4 to 1.7 for 
the excellent pictures, that the D,ax is not less 
than 1.8 for the most of the qualified one, and 
that the D,4, may be 2.0 for pictures with 
special subjectives . The lower limit of D, is 
controlled by AD and Dyin, and it need not be 
defined definitely. 
5.4 Image contrast AD 
Tab. 1 shows that, it is benefit to raise D, among 
proper density range. It can improve the 
114 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B1. Vienna 1996 
  
reso. 
and 
capa 
shov 
abur 
goo 
are 1 
ster 
is le: 
too 
than 
0.7 1 
5.5 
deve 
as p 
tran 
deta 
reso 
nois 
shoi 
  
[1] 
Sci 
197 
[2] 
Aer 
Sta