Image 27

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 01:08:09
# Resolution   : 2048 x 1536 in jpeg (2064x1540 in pgm/27.pgm)
# Focal length : 15.2mm
# Exposure time: 4.000 s 
# Aperture     : f/3.2
# 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   -44   -56   -48      -0.00722  -0.00765  -0.0114  -0.0103  -0.00597
 10   -24   -20   -28   -24      -0.00394  -0.00348  -0.00570  -0.00516  -0.00341
 50     4     4     4     4       6.56E-4   6.96E-4   8.14E-4   8.60E-4   6.09E-4
 90    28    28    32    28       0.00459   0.00487   0.00651   0.00602   0.00402
 99    52    48    60    52       0.00853   0.00835   0.0122   0.0112   0.00743
100 16324 16332 16344 16324       2.68     2.84     3.33     3.51     2.48  
# flux from 3.62 sr ( 4.73E-6 sr/4px) is  0.00255 lx (SQM 0.00121 nt, 19.88 mag);
# tilewise luminance  8.29E-4 cd/m2 with rel. SD  202 % (summing pixels below 16380)
# dark frame dark/4s.pgm subtracted from all values
# Yell average=   5.2  minimum= -344  maximum=16324   over 16380:  52
# Cyan average=   3.6  minimum= -444  maximum=16332   over 16380:  73
# Gree average=   3.2  minimum= -304  maximum=16344   over 16380:  82
# Mage average=   3.6  minimum= -156  maximum=16324   over 16380:  61

End of results of "raw2lum" (version 1.22) with parameters:
  -c YCGM -fa -w 7.3 -fc0.214 -o 16380 -d dark/4s.pgm -sm200 -nh -i 27.txt -e 27.eps -n 27.ppm -t156 -c 3412 -s64 pgm/27.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)