Image 25


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 01:05:34
# Resolution   : 2048 x 1536 in jpeg (2064x1540 in pgm/25.pgm)
# Focal length : 15.2mm
# Exposure time: 0.200 s  (1/5)
# 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      -0.125   -0.132   -0.187   -0.181   -0.106 
 10   -20   -20   -26   -22      -0.0656  -0.0696  -0.106   -0.0946  -0.0536
 50     0     0     0     0       0.00     0.00     0.00     0.00     0.00  
 90    22    20    26    24       0.0722   0.0696   0.106    0.103    0.0621
 99    38    38    50    44       0.125    0.132    0.203    0.189    0.101 
100 16330 16308 16314 16310       53.6     56.7     66.4     70.1     49.8  
# flux from 3.62 sr ( 4.73E-6 sr/4px) is  0.00894 lx (SQM 0.00403 nt, 18.57 mag);
# tilewise luminance  0.00267 cd/m2 with rel. SD  358 % (summing pixels below 16380)
# dark frame dark/off.pgm subtracted from all values
# Yell average=   1.0  minimum=  -84  maximum=16330   over 16380:   4
# Cyan average=   0.5  minimum=  -84  maximum=16308   over 16380:   1
# Gree average=   0.7  minimum=  -92  maximum=16314   over 16380:   4
# Mage average=   0.4  minimum= -102  maximum=16310   over 16380:   3

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 25.txt -e 25.eps -n 25.ppm -t156 -c 3412 -s64 pgm/25.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)