Image 48


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 01:33:48
# Resolution   : 2048 x 1536 in jpeg (2064x1540 in pgm/48.pgm)
# Focal length : 20.6mm
# Exposure time: 4.000 s 
# Aperture     : f/3.7
# 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    16    -4   -12    -4       0.00326  -8.64E-4  -0.00303  -0.00107   0.00515
 10    56    32    28    36       0.0114   0.00691   0.00707   0.00961   0.0127
 50   276   140   148   176       0.0562   0.0302   0.0374   0.0470   0.0619
 90   832   420   436   552       0.169    0.0907   0.110    0.147    0.187 
 99  4828  2876  2728  3416       0.984    0.621    0.689    0.912    1.07  
100 16356 16340 16372 16344       3.33     3.53     4.14     4.36     3.09  
# flux from 0.0873 sr ( 1.11E-7 sr/4px) is  0.00905 lx;
# tilewise luminance  0.106 cd/m2 with rel. SD  127 % (summing pixels below 16380)
# dark frame dark/4s.pgm subtracted from all values
# Yell average= 464.1  minimum= -268  maximum=16356   over 16380: 1108
# Cyan average= 255.4  minimum= -440  maximum=16340   over 16380: 1345
# Gree average= 259.9  minimum= -196  maximum=16372   over 16380: 1919
# Mage average= 316.8  minimum= -108  maximum=16344   over 16380: 1148

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 48.txt -e 48.eps -n 48.ppm -t168 -c 3412 -s64 pgm/48.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)