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Entry  Sat Jul 15 01:28:53 2017, jigyasa, Update, Cameras, BRDF Calibrations 
    Reply  Sat Jul 15 13:40:59 2017, rana, Update, Cameras, BRDF Calibrations 
       Reply  Sun Jul 16 11:58:36 2017, jigyasa, Update, Cameras, BRDF Calibrations 
          Reply  Sun Jul 16 12:09:47 2017, jigyasa, Update, Cameras, BRDF Calibrations 
Message ID: 13122     Entry time: Sun Jul 16 12:09:47 2017     In reply to: 13121
Author: jigyasa 
Type: Update 
Category: Cameras 
Subject: BRDF Calibrations 

With this idea in mind, we can now actually take images of the illuminated paper at different scattering angles, assume BRDF is the constant value of (1/pi per steradian), 

then scattered power Ps= BRDF * Pi cosθ * Ω, where Pi is the incident power, Ω is the solid angle of the camera and θ is the scattering angle at which measurement is taken. This must also equal the sum of pixel counts divided by the exposure time multiplied by some calibration factor. 

From these two equations we can obtain the calibration factor of the CCD. And for further BRDF measurements, scale the pixel count/ exposure by this calibration factor.  

Quote:

 

From what I understood froom my reading, [Large-angle scattered light measurements for quantum-noise filter cavity design studies(Refer https://arxiv.org/abs/1204.2528)], we do the white paper test in order to calibrate for the radiometric response, i.e. the response of the CCD sensor to radiance.‘We convert the image counts measured by the CCD camera into a calibrated measure of scatter. To do this we measure the scattered light from a diffusing sample twice, once with the CCD camera and once with a calibrated power meter. We then compare their readings.’

But thinking about this further, if we assume that the BRDF remains unscaled and estimate the scattered power from the images, we get a calibration factor for the scattered power and the angle dependence of the scattered power!

Quote:

Power meter only needed to measure power going into the paper not out. We use the BRDF of paper to estimate the power going out given the power going in.

 

 

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