Image 31


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 02:51:34
# Resolution   : 1280 x 960 in jpeg (1424x1076 in pgm/31.pgm)
# Focal length : 10.7mm  (35mm equivalent: 72mm)
# 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   -43   -40   -41   -49        -0.0494  -0.0269  -0.0511  -0.0348
 10    -5    -3    -4   -16        -0.00575  -0.00233  -0.0167  -0.00352
 50    82    72    72    22         0.0943   0.0478   0.0229   0.0641
 90   630   475   475    90         0.724    0.316    0.0939   0.459 
 99  1378  1029  1028   177         1.58     0.683    0.185    0.999 
100 15869 15866 15866 15867         18.2     10.5     16.6     13.2  
# flux from 0.186*0.87 sr ( 2.44E-7 sr/4px) is  0.0325 lx ( 0.0346 lx tilewise);
# tilewise luminance  0.205 cd/m2 with rel. SD  110 % (summing pixels below 15850 and with non-zero green: there is 87.3 % of them)
# Fuji Devignetting: 2 # dark frame dark/42.pgm subtracted from all values
# Red  average= 268.7  minimum= -121  maximum=15869   over 15850: 443 zero: 10.3 %
# GrUp average= 213.5  minimum= -129  maximum=15866   over 15850: 361 zero: 12.9 %
# GrDw average= 212.6  minimum= -105  maximum=15866   over 15850: 371 zero: 12.5 %
# Blue average=  43.4  minimum= -120  maximum=15867   over 15850: 184 zero: 21.2 %

End of results of "raw2lum" (version 1.22) with parameters:
  -c fuji -fa -d dark/42.pgm -sm100 -nh -nt -i 31.txt -e 31.eps -n 31.ppm -t 118 -s71:76 pgm/31.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)