Estimating Radiance from Pixel Values
The file acal.dat
has the calibration parameters which translate average
pixel values into radiance values. This file has the following format
1 gain offset
2 gain offset
61 gain offset
where the first number in the row is the sample number
and the subsequent numbers in the row
are the gain and offset used to transform pixel values into radiance
values in the following manner:
radiance = gain*pixel + offset .
The term radiance the total radiance
in watts/(steridian m^2) summed over the wavelength range 380nm-780nm.
The term pixel is taken as the average of the R/G/B pixel values.
A similar file ccal.dat has the color calibration parameters
in the following format:
1 Rgain Roffset Ggain Goffset Bgain Boffset
2 Rgain Roffset Ggain Goffset Bgain Boffset
61 Rgain Roffset Ggain Goffset Bgain Boffset
These color calibration parameters are used
to convert R/G/B pixel values into R/G/B radiance
in the following manner:
R_radiance = Rgain*R_pixel + Roffset
G_radiance = Ggain*G_pixel + Goffset
B_radiance = Bgain*B_pixel + Boffset
The terms R_radiance,G_radiance,B_radiance
are the guassian weighted average radiance over the wavelength range 380nm-780nm,
where the guassian weights are the estimated R/G/B sensitivity curves of
the video camera.
The brightness of the lamp is also estimated so that
BRDF can be obtained from the radiance values.
This estimation was done by recording the radiance
from a Kodak 18% gray card using a photometer.
During the experiments 3 lamps were used (due
to the limited lifetime of each lamp).
The following table lists the three lamps along
with the samples that were measured with that lamp and
the estimate brightness E0.
Lamp_Number Samples_Measured E0
1 1-8 9.56379
2 9-44 57.664
3 45-61 13.0799
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