Image 18


original	lighter	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    : 2006:06:29 02:43:23
# Resolution   : 1280 x 960 in jpeg (1424x1076 in pgm/18.pgm)
# Focal length :  5.7mm  (35mm equivalent: 39mm)
# CCD width    : 5.32mm
# Exposure time: 2.000 s 
# Aperture     : f/2.8
# ISO equiv.   : 200

# Selected image percentils         L=(1.730*0.35*R+1.000*0.65*G+1.570*0.00*B)* 1.66E-4
# %    R     G1    G2    B readings  R        G        B        L / cd/m2
  1   -50   -45   -44   -54        -0.0144  -0.00739  -0.0141  -0.00983
 10   -15   -11   -11   -22        -0.00431  -0.00183  -0.00574  -0.00270
 50    37    33    33    13         0.0106   0.00548   0.00339   0.00728
 90   415   333   333    78         0.119    0.0553   0.0203   0.0777
 99  2992  2271  2273   326         0.860    0.377    0.0850   0.546 
100 15869 15866 15866 15867         4.56     2.64     4.14     3.31  
# flux from 0.654*0.81 sr ( 8.59E-7 sr/4px) is  0.0228 lx ( 0.0244 lx tilewise);
# tilewise luminance  0.0340 cd/m2 with rel. SD  218 % (summing pixels below 15850 and with non-zero green: there is 81.0 % of them)
# Fuji Devignetting: 1 # dark frame dark/43.pgm subtracted from all values
# Red  average= 225.2  minimum= -147  maximum=15869   over 15850: 408 zero: 15.7 %
# GrUp average= 186.7  minimum= -116  maximum=15866   over 15850: 368 zero: 19.2 %
# GrDw average= 186.5  minimum= -130  maximum=15866   over 15850: 370 zero: 18.8 %
# Blue average=  41.2  minimum= -364  maximum=15867   over 15850:  80 zero: 25.3 %

End of results of "raw2lum" (version 1.22) with parameters:
  -c fuji -fa -d dark/43.pgm -sm100 -nh -nt -i 18.txt -e 18.eps -n 18.ppm -t 118 -s71:76 pgm/18.pgm

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)