Image 40


original	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    : 2005:08:05 01:21:48
# Resolution   : 2048 x 1536 in jpeg (2064x1540 in pgm/40.pgm)
# Focal length :  8.2mm
# Exposure time: 4.000 s 
# Aperture     : f/2.5
# ISO equiv.   : 100

#c li count  min   Yav   max  ovf   min  Cav    max   ovf   min  Gav    max   ovf   min  Mav   max   ovf
# %    Y     C     G     M readings  Y        C        G        M        L / cd/m2
  1   -40   -40   -52   -44      -0.00372  -0.00394  -0.00600  -0.00536  -0.00304
 10   -16   -20   -24   -20      -0.00149  -0.00197  -0.00277  -0.00244  -0.00110
 50    12     8     8     8       0.00112   7.89E-4   9.23E-4   9.75E-4   0.00117
 90    40    32    40    36       0.00372   0.00315   0.00461   0.00439   0.00345
 99    68    56    68    64       0.00632   0.00552   0.00784   0.00780   0.00587
100 16348 16340 16336 16320       1.52     1.61     1.88     1.99     1.41  
# flux from 0.528 sr ( 7.01E-7 sr/4px) is  6.46E-4 lx;
# tilewise luminance  0.00115 cd/m2 with rel. SD  135 % (summing pixels below 16380)
# dark frame dark/4s.pgm subtracted from all values
# Yell average=  12.7  minimum= -292  maximum=16348   over 16380:  32
# Cyan average=   7.1  minimum= -424  maximum=16340   over 16380:  40
# Gree average=   8.3  minimum= -208  maximum=16336   over 16380:  42
# Mage average=   8.9  minimum= -212  maximum=16320   over 16380:  27

End of results of "raw2lum" (version 1.22) with parameters:
  -c YCGM -fa -w 7.3 -fc1.03 -o 16380 -d dark/4s.pgm -sm200 -nh -i 40.txt -e 40.eps -n 40.ppm -t168 -c 3412 -s64 pgm/40.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)