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

[Greg Ward]

Very quickly, you can look at the "Tools for Materials" section of the SIGGRAPH '96 course notes here:

	http://radsite.lbl.gov/radiance/refer/sg96crs.pdf

The Radiance tool you want to check out is macbethcal, and you can look in src/px/macbethcal.c to find the MacBeth color checker measurements.  There are some tips as well in Chapter 5 of "Rendering with Radiance" if you have that.

On a Mac, you can use Photosphere from <www.anyhere.com> to calibrate a camera, as described in Mehlika Inanici's technical reort:

	http://gaia.lbl.gov/btech/papers/57545.pdf

Best,
-Greg

> From: "Ilya A. Zimnovich" <webmaster at audice.com>
> Date: November 3, 2010 12:14:30 PM PDT
> 
> 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