Image 19

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 00:52:26
# Resolution   : 2048 x 1536 in jpeg (2064x1540 in pgm/19.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   -44   -45   -85   -76      -2.93E-4  -3.18E-4  -7.02E-4  -6.63E-4  -1.70E-4
 10   -20   -20   -35   -31      -1.33E-4  -1.41E-4  -2.89E-4  -2.71E-4  -8.65E-5
 50    12     9     4     4       8.00E-5   6.36E-5   3.31E-5   3.49E-5   9.40E-5
 90   100    77    65    67       6.66E-4   5.44E-4   5.37E-4   5.85E-4   7.05E-4
 99   243   149   145   157       0.00162   0.00105   0.00120   0.00137   0.00175
100 16288 11684 16155 15803       0.109    0.0825   0.133    0.138    0.101 
# flux from 6.28 sr ( 1.62E-5 sr/4px) is  0.00158 lx (SQM 6.04E-4 nt, 20.63 mag);
# tilewise luminance  2.12E-4 cd/m2 with rel. SD  165 % (summing pixels below 16380)
# dark frame dark/1m.pgm subtracted from all values
# Yell average=  28.4  minimum= -512  maximum=16288   over 16380:   1
# Cyan average=  19.5  minimum= -512  maximum=11684   over 16380:   1
# Gree average=  10.5  minimum= -512  maximum=16155   over 16380:   3
# Mage average=  11.5  minimum= -512  maximum=15803   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 19.txt -e 19.eps -n 19.ppm -t156 -c 3412 -s64 pgm/19.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)