Image 23


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 02:46:03
# Resolution   : 1280 x 960 in jpeg (1424x1076 in pgm/23.pgm)
# Focal length :  9.4mm  (35mm equivalent: 64mm)
# 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   -45   -42   -42   -50        -0.0517  -0.0279  -0.0522  -0.0362
 10    -9    -7    -7   -18        -0.0103  -0.00465  -0.0188  -0.00664
 50    60    56    57    16         0.0690   0.0375   0.0167   0.0485
 90   444   342   343    80         0.510    0.228    0.0834   0.327 
 99  1053   808   805   166         1.21     0.536    0.173    0.772 
100 15869 15866 15866 15867         18.2     10.5     16.6     13.2  
# flux from 0.241*0.84 sr ( 3.16E-7 sr/4px) is  0.0296 lx ( 0.0323 lx tilewise);
# tilewise luminance  0.135 cd/m2 with rel. SD  108 % (summing pixels below 15850 and with non-zero green: there is 84.2 % of them)
# Fuji Devignetting: 2 # dark frame dark/42.pgm subtracted from all values
# Red  average= 193.7  minimum= -143  maximum=15869   over 15850: 452 zero: 13.5 %
# GrUp average= 159.3  minimum= -111  maximum=15866   over 15850: 408 zero: 16.2 %
# GrDw average= 158.9  minimum= -111  maximum=15866   over 15850: 395 zero: 15.5 %
# Blue average=  37.3  minimum= -115  maximum=15867   over 15850: 144 zero: 24.5 %

End of results of "raw2lum" (version 1.22) with parameters:
  -c fuji -fa -d dark/42.pgm -sm100 -nh -nt -i 23.txt -e 23.eps -n 23.ppm -t 118 -s71:76 pgm/23.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)