Image 29


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 01:09:12
# Resolution   : 2048 x 1536 in jpeg (2064x1540 in pgm/29.pgm)
# Focal length : 15.2mm
# Exposure time: 0.017 s  (1/60)
# 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      -1.50    -1.59    -2.25    -2.17    -1.27  
 10   -22   -22   -26   -24      -0.866   -0.918   -1.27    -1.24    -0.745 
 50     0     0     0     0       0.00     0.00     0.00     0.00     0.00  
 90    22    20    24    22       0.866    0.835    1.17     1.14     0.775 
 99    40    40    46    40       1.58     1.67     2.25     2.06     1.37  
100  3366  1806  2898  1554        133     75.4      142     80.2      130  
# flux from 3.62 sr ( 4.73E-6 sr/4px) is  0.0184 lx (SQM 0.00747 nt, 17.90 mag);
# tilewise luminance  0.00486 cd/m2 with rel. SD 1.06E3 % (summing pixels below 16380)
# dark frame dark/off.pgm subtracted from all values
# Yell average=  -0.0  minimum=  -92  maximum= 3366   over 16380:   0
# Cyan average=  -0.2  minimum= -100  maximum= 1806   over 16380:   0
# Gree average=  -0.6  minimum= -102  maximum= 2898   over 16380:   0
# Mage average=  -0.7  minimum= -262  maximum= 1554   over 16380:   0

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 29.txt -e 29.eps -n 29.ppm -t156 -c 3412 -s64 pgm/29.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)