Image 20


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 02:44:33
# Resolution   : 1280 x 960 in jpeg (1424x1076 in pgm/20.pgm)
# Focal length :  5.7mm  (35mm equivalent: 39mm)
# CCD width    : 5.32mm
# Exposure time: 0.500 s  (1/2)
# 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)* 6.64E-4
# %    R     G1    G2    B readings  R        G        B        L / cd/m2
  1   -50   -47   -47   -52        -0.0575  -0.0312  -0.0542  -0.0404
 10   -18   -15   -16   -22        -0.0207  -0.0103  -0.0229  -0.0139
 50    26    23    24     7         0.0299   0.0156   0.00730   0.0206
 90   314   241   241    61         0.361    0.160    0.0636   0.230 
 99   456   353   355   109         0.524    0.235    0.114    0.336 
100 15869 15866 15866 15867         18.2     10.5     16.6     13.2  
# flux from 0.654*0.74 sr ( 8.59E-7 sr/4px) is  0.0422 lx ( 0.0475 lx tilewise);
# tilewise luminance  0.0883 cd/m2 with rel. SD  118 % (summing pixels below 15850 and with non-zero green: there is 73.7 % of them)
# Fuji Devignetting: 1 # dark frame dark/42.pgm subtracted from all values
# Red  average= 117.6  minimum= -125  maximum=15869   over 15850:  24 zero: 23.4 %
# GrUp average=  96.5  minimum= -129  maximum=15866   over 15850:  18 zero: 26.9 %
# GrDw average=  95.1  minimum= -115  maximum=15866   over 15850:  24 zero: 25.7 %
# Blue average=  22.5  minimum= -122  maximum=15867   over 15850:   6 zero: 32.1 %

End of results of "raw2lum" (version 1.22) with parameters:
  -c fuji -fa -d dark/42.pgm -sm100 -nh -nt -i 20.txt -e 20.eps -n 20.ppm -t 118 -s71:76 pgm/20.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)