Image 22

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 00:56:52
# Resolution   : 2048 x 1536 in jpeg (2064x1540 in pgm/22.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   -33   -35   -41   -37      -2.20E-4  -2.47E-4  -3.39E-4  -3.23E-4  -1.84E-4
 10   -13   -13   -16   -13      -8.66E-5  -9.18E-5  -1.32E-4  -1.13E-4  -7.29E-5
 50    20    17    24    21       1.33E-4   1.20E-4   1.98E-4   1.83E-4   1.14E-4
 90   104    83    85    83       6.93E-4   5.86E-4   7.02E-4   7.25E-4   6.90E-4
 99   165   125   140   133       0.00110   8.83E-4   0.00116   0.00116   0.00108
100  9736  6499  5611  5396       0.0649   0.0459   0.0464   0.0471   0.0704
# flux from 6.28 sr ( 1.62E-5 sr/4px) is  0.00152 lx (SQM 5.32E-4 nt, 20.77 mag);
# tilewise luminance  2.25E-4 cd/m2 with rel. SD  126 % (summing pixels below 16380)
# dark frame dark/1m.pgm subtracted from all values
# Yell average=  35.2  minimum= -512  maximum= 9736   over 16380:   2
# Cyan average=  27.7  minimum= -293  maximum= 6499   over 16380:   1
# Gree average=  30.2  minimum= -512  maximum= 5611   over 16380:   0
# Mage average=  28.9  minimum= -512  maximum= 5396   over 16380:   1

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 22.txt -e 22.eps -n 22.ppm -t156 -c 3412 -s64 pgm/22.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)