Image 28


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 01:08:38
# Resolution   : 2048 x 1536 in jpeg (2064x1540 in pgm/28.pgm)
# Focal length : 15.2mm
# Exposure time: 0.250 s  (1/4)
# Aperture     : f/3.2
# 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   -38   -38   -46   -42      -0.0998  -0.106   -0.150   -0.144   -0.0848
 10   -20   -20   -26   -22      -0.0525  -0.0557  -0.0847  -0.0757  -0.0429
 50     0     0     0     0       0.00     0.00     0.00     0.00     0.00  
 90    22    22    26    22       0.0578   0.0612   0.0847   0.0757   0.0497
 99    40    40    48    42       0.105    0.111    0.156    0.144    0.0896
100 16310 16306 16302 16302       42.8     45.4     53.1     56.1     39.7  
# flux from 3.62 sr ( 4.73E-6 sr/4px) is  0.00663 lx (SQM 0.00333 nt, 18.78 mag);
# tilewise luminance  0.00213 cd/m2 with rel. SD  369 % (summing pixels below 16380)
# dark frame dark/off.pgm subtracted from all values
# Yell average=   0.7  minimum=  -82  maximum=16310   over 16380:   2
# Cyan average=   0.8  minimum=  -84  maximum=16306   over 16380:   1
# Gree average=   0.3  minimum=  -92  maximum=16302   over 16380:   6
# Mage average=   0.4  minimum=  -86  maximum=16302   over 16380:   2

End of results of "raw2lum" (version 1.22) with parameters:
  -c YCGM -fa -w 7.3 -fc0.214 -o 16380 -d dark/off.pgm -sm200 -nh -i 28.txt -e 28.eps -n 28.ppm -t156 -c 3412 -s64 pgm/28.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)