Image 23

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 00:58:14
# Resolution   : 2048 x 1536 in jpeg (2064x1540 in pgm/23.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   -32   -40   -33      -2.20E-4  -2.26E-4  -3.31E-4  -2.88E-4  -1.87E-4
 10   -11   -11   -11    -9      -7.33E-5  -7.77E-5  -9.09E-5  -7.86E-5  -6.80E-5
 50    39    32    39    36       2.60E-4   2.26E-4   3.22E-4   3.14E-4   2.41E-4
 90   137   104   111   109       9.13E-4   7.35E-4   9.17E-4   9.52E-4   9.12E-4
 99   264   167   195   203       0.00176   0.00118   0.00161   0.00177   0.00180
100 16295 16292 16304 16305       0.109    0.115    0.135    0.142    0.101 
# flux from 6.28 sr ( 1.62E-5 sr/4px) is  0.00197 lx (SQM 5.03E-4 nt, 20.83 mag);
# tilewise luminance  3.70E-4 cd/m2 with rel. SD  117 % (summing pixels below 16380)
# dark frame dark/1m.pgm subtracted from all values
# Yell average=  56.2  minimum= -512  maximum=16295   over 16380:   7
# Cyan average=  41.6  minimum= -301  maximum=16292   over 16380:  11
# Gree average=  46.1  minimum= -512  maximum=16304   over 16380:   7
# Mage average=  45.7  minimum= -512  maximum=16305   over 16380:   6

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 23.txt -e 23.eps -n 23.ppm -t156 -c 3412 -s64 pgm/23.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)