Radiometric Calibration

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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