Image 42


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 01:22:25
# Resolution   : 2048 x 1536 in jpeg (2064x1540 in pgm/42.pgm)
# Focal length :  8.2mm
# Exposure time: 0.017 s  (1/60)
# 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   -38   -38   -48   -42      -0.848   -0.899   -1.33    -1.23    -0.704 
 10   -22   -22   -26   -24      -0.491   -0.521   -0.720   -0.702   -0.423 
 50     0     0     0     0       0.00     0.00     0.00     0.00     0.00  
 90    22    20    26    22       0.491    0.473    0.720    0.643    0.423 
 99    40    38    48    42       0.893    0.899    1.33     1.23     0.762 
100 16308 10586 11088 12150        364      250      307      355      381  
# flux from 0.528 sr ( 7.01E-7 sr/4px) is  0.00330 lx;
# tilewise luminance  0.00784 cd/m2 with rel. SD  497 % (summing pixels below 16380)
# dark frame dark/off.pgm subtracted from all values
# Yell average=   0.2  minimum=  -82  maximum=16308   over 16380:   0
# Cyan average=  -0.3  minimum=  -88  maximum=10586   over 16380:   0
# Gree average=  -0.1  minimum=  -96  maximum=11088   over 16380:   2
# Mage average=  -0.2  minimum=  -92  maximum=12150   over 16380:   0

End of results of "raw2lum" (version 1.22) with parameters:
  -c YCGM -fa -w 7.3 -fc1.03 -o 16380 -d dark/off.pgm -sm200 -nh -i 42.txt -e 42.eps -n 42.ppm -t168 -c 3412 -s64 pgm/42.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)