Image 17

original colour coded

and with an inserted data grid:

(in the middle of tiles, median of raw G-pixels values is given, the bottom value is the tile luminance divided by one candela per square meter). 
# Date/Time    : 2005:08:05 00:48:12
# Resolution   : 2048 x 1536 in jpeg (2064x1540 in pgm/17.pgm)
# Focal length :  8.2mm
# Exposure time:60.120 s 
# Aperture     : f/2.5
# ISO equiv.   : 100

#c li count  min   Yav   max  ovf   min  Cav    max   ovf   min  Gav    max   ovf   min  Mav   max   ovf
# %    Y     C     G     M readings  Y        C        G        M        L / cd/m2
  1   -53   -53  -149  -132      -3.53E-4  -3.74E-4  -0.00123  -0.00115  -8.98E-5
 10   -20   -21   -44   -37      -1.33E-4  -1.48E-4  -3.63E-4  -3.23E-4  -6.42E-5
 50    27    21     9     9       1.80E-4   1.48E-4   7.44E-5   7.86E-5   2.12E-4
 90   127    93    79    80       8.46E-4   6.57E-4   6.53E-4   6.98E-4   9.04E-4
 99   255   153   147   160       0.00170   0.00108   0.00121   0.00140   0.00184
100 16301 16308 16309 16297       0.109    0.115    0.135    0.142    0.101 
# flux from 6.28 sr ( 1.62E-5 sr/4px) is  0.00190 lx (SQM 4.80E-4 nt, 20.88 mag);
# tilewise luminance  3.87E-4 cd/m2 with rel. SD  169 % (summing pixels below 16380)
# dark frame dark/1m.pgm subtracted from all values
# Yell average=  44.9  minimum= -512  maximum=16301   over 16380:  14
# Cyan average=  31.1  minimum= -512  maximum=16308   over 16380:  19
# Gree average=  12.5  minimum= -512  maximum=16309   over 16380:  20
# Mage average=  16.1  minimum= -512  maximum=16297   over 16380:  15

End of results of "raw2lum" (version 1.22) with parameters:
  -c YCGM -fa -w 7.3 -fc0.214 -o 16380 -d dark/1m.pgm -sm200 -nh -i 17.txt -e 17.eps -n 17.ppm -t156 -c 3412 -s64 pgm/17.pgm
Luminance scale / 1 cd/m<sup>2</sup>
Logarithmic luminance scale (the unit is candela per square meter) – intensities of snow illuminance in lux would be obtained by multiplying the numeric value of luminance by 3.6. For asphalt, such a coefficient is between 20 and 40 (or much less, for specular reflection of distant lamps)