Image 04


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    : 2005:08:04 14:42:51
# Resolution   : 2048 x 1536 in jpeg (2064x1540 in pgm/04.pgm)
# Focal length :  8.2mm
# Exposure time: 0.004 s  (1/250)
# Aperture     : f/7.0
# 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   -22   -22   -30   -26      -17.3    -18.3    -29.2    -26.7    -13.7  
 10     2     2    -2     0       1.57     1.66    -1.95     0.00     2.63  
 50  1112   980   870   776        873      816      847      798      881  
 90  2860  2764  2306  2232       2.25E3   2.30E3   2.25E3   2.30E3   2.25E3
 99  3432  3380  2806  2674       2.69E3   2.81E3   2.73E3   2.75E3   2.68E3
100 12406 12882 10544 10038       9.74E3   1.07E4   1.03E4   1.03E4   9.58E3
# flux from 6.28 sr ( 1.62E-5 sr/4px) is  6.40E3 lx (SQM 2.05E3 nt,  4.30 mag);
# tilewise luminance   991 cd/m2 with rel. SD 97.2 % (summing pixels below 16380)
# dark frame dark/off.pgm subtracted from all values
# Yell average=1291.8  minimum=  -66  maximum=12406   over 16380:   0
# Cyan average=1252.6  minimum=  -68  maximum=12882   over 16380:   0
# Gree average=1042.3  minimum=  -94  maximum=10544   over 16380:   0
# Mage average=1007.7  minimum=  -78  maximum=10038   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 04.txt -e 04.eps -n 04.ppm -t156 -c 3412 -s64 pgm/04.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)