Image 21


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 02:45:03
# Resolution   : 1280 x 960 in jpeg (1424x1076 in pgm/21.pgm)
# Focal length : 15.4mm  (35mm equivalent: 104mm)
# CCD width    : 5.32mm
# Exposure time: 2.000 s 
# Aperture     : f/3.2
# ISO equiv.   : 200

# Selected image percentils         L=(1.730*0.35*R+1.000*0.65*G+1.570*0.00*B)* 2.17E-4
# %    R     G1    G2    B readings  R        G        B        L / cd/m2
  1   -45   -40   -41   -52        -0.0169  -0.00879  -0.0177  -0.0116
 10    -7    -5    -5   -19        -0.00263  -0.00108  -0.00647  -0.00162
 50    61    52    53    18         0.0229   0.0114   0.00613   0.0154
 90   464   351   351    80         0.174    0.0761   0.0272   0.110 
 99  1834  1349  1351   207         0.688    0.293    0.0705   0.431 
100 15869 15866 15866 15867         5.96     3.44     5.40     4.32  
# flux from 0.0900*0.86 sr ( 1.18E-7 sr/4px) is  0.00372 lx ( 0.00411 lx tilewise);
# tilewise luminance  0.0494 cd/m2 with rel. SD  108 % (summing pixels below 15850 and with non-zero green: there is 86.4 % of them)
# Fuji Devignetting: 2 # dark frame dark/43.pgm subtracted from all values
# Red  average= 193.9  minimum= -203  maximum=15869   over 15850: 555 zero: 10.3 %
# GrUp average= 156.2  minimum= -117  maximum=15866   over 15850: 465 zero: 13.6 %
# GrDw average= 157.3  minimum= -119  maximum=15866   over 15850: 420 zero: 13.7 %
# Blue average=  39.1  minimum= -293  maximum=15867   over 15850:  73 zero: 21.7 %

End of results of "raw2lum" (version 1.22) with parameters:
  -c fuji -fa -d dark/43.pgm -sm100 -nh -nt -i 21.txt -e 21.eps -n 21.ppm -t 118 -s71:76 pgm/21.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)