Image 01

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    : 2005:08:04 14:40:46
# Resolution   : 2048 x 1536 in jpeg (2064x1540 in pgm/01.pgm)
# Focal length : 11.0mm
# Exposure time: 0.004 s  (1/250)
# Aperture     : f/7.7
# 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    30    34    22    22       28.5     34.2     25.9     27.4     29.3  
 10   300   342   266   262        285      344      313      326      277  
 50  2812  2714  2260  2190       2.67E3   2.73E3   2.66E3   2.73E3   2.67E3
 90 15812 16292 14098 14140       1.50E4   1.64E4   1.66E4   1.76E4   1.45E4
 99 16314 16316 16316 16314       1.55E4   1.64E4   1.92E4   2.03E4   1.44E4
100 16342 16342 16354 16344       1.55E4   1.65E4   1.93E4   2.03E4   1.44E4
# flux from 4.87 sr ( 9.03E-6 sr/4px) is  1.13E4 lx (SQM 3.27E3 nt,  3.80 mag);
# tilewise luminance  4.43E3 cd/m2 with rel. SD 99.2 % (summing pixels below 16380)
# dark frame dark/off.pgm subtracted from all values
# Yell average=4321.4  minimum=  -40  maximum=16342   over 16380: 45679
# Cyan average=4196.8  minimum=  -38  maximum=16342   over 16380: 43837
# Gree average=4112.2  minimum=  -60  maximum=16354   over 16380: 71506
# Mage average=4112.6  minimum=  -44  maximum=16344   over 16380: 94477

End of results of "raw2lum" (version 1.22) with parameters:
  -c YCGM -fa -w 7.3 -fc0.214 -o 16380 -d dark/off.pgm -sm200 -nh -i 01.txt -e 01.eps -n 01.ppm -t156 -c 3412 -s64 pgm/01.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)