[Radiance-general] Diffuse reflectance measurements and GretagMacbeth ColorChecker reflectance values

[Ilya A. Zimnovich]

Dear mailing list members,

I have been experimenting with our new scientific grade CCD camera which 
I suppose can be used as an imaging photometer. Yes, after some 
extensive calibration!

I would like to take some measurements of diffuse reflectance. The 
classical setup will require an integrating sphere. Well... the 
University I work at will not afford such an expensive device. I'm sure 
there would be another way to estimate it. I guess it is possible to 
acquire BRDF and to make some diffuse reflectance estimation?

Below are my questions:

1. Is there way to estimate diffuse reflectance without using of 
integrating sphere? Also, to some extent, can the reflectance measured 
under overcast sky conditions be referred to as diffuse reflectance?

2. How do you calibrate your CCD cameras for taking luminance measurements?

3. With uncalibrated camera, I guess the reflectance values can be 
estimated using HDR shots of GretagMacbeth ColorChecker chart as 
reference. The ColorChecker chart's reflectance values are known, right? 
So, it is possible to compare the values from the shot of a sample 
against the values from the shot of the chart to estimate the 
reflectance of the sample?! But where can I get the GretagMacbeth 
ColorChecker Rendition chart's RGB reflectance values? I wonder if 
anyone have measured them?!

4. What are in the "macbeth_spec.hdr" and "macbeth_pub.hdr" files? What 
data are in these files?

5. Having estimated BRDF for a particular material sample can we 
estimate the material's diffuse reflectance?

Thanks,
Ilya