Image 54


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 03:07:28
# Resolution   : 1280 x 960 in jpeg (1424x1076 in pgm/54.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   -54   -51   -52   -54        -0.0621  -0.0342  -0.0563  -0.0440
 10   -24   -21   -22   -25        -0.0276  -0.0143  -0.0261  -0.0189
 50     7     5     5     0         0.00805   0.00332   0.00     0.00498
 90    89    80    81    49         0.102    0.0535   0.0511   0.0706
 99   825   628   627   111         0.948    0.417    0.116    0.603 
100 15876 15873 15873 15874         18.2     10.5     16.6     13.2  
# flux from 0.654*0.65 sr ( 8.59E-7 sr/4px) is  0.0227 lx ( 0.0273 lx tilewise);
# tilewise luminance  0.0389 cd/m2 with rel. SD  218 % (summing pixels below 15850 and with non-zero green: there is 65.2 % of them)
# Fuji Devignetting: 1 # dark frame dark/42.pgm subtracted from all values
# Red  average=  68.6  minimum= -131  maximum=15876   over 15850: 253 zero: 31.7 %
# GrUp average=  59.8  minimum= -108  maximum=15873   over 15850: 208 zero: 35.0 %
# GrDw average=  59.3  minimum= -124  maximum=15873   over 15850: 204 zero: 34.5 %
# Blue average=  17.8  minimum= -128  maximum=15874   over 15850:  40 zero: 38.1 %

End of results of "raw2lum" (version 1.22) with parameters:
  -c fuji -fa -d dark/42.pgm -sm100 -nh -nt -i 54.txt -e 54.eps -n 54.ppm -t 118 -s71:76 pgm/54.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)