[Radiance-general] Reflectance meausrement using macbethcal utility

[Jia Hu]

Hi Greg,

 I do not require a high accuracy of reflectance. How about If I use pvalue
to calculate the average of RGB values for a surface of interest in the HDR
image, and then use the average to estimate the surface reflectance?

Thanks :)
Jia


On Wed, Jul 30, 2014 at 12:09 PM, Greg Ward <gregoryjward at gmail.com> wrote:

> It's all explained (as best I can) in the macbethcal man page:
>
>         http://radsite.lbl.gov/radiance/man_html/macbethcal.1.html
>
> You give it an HDR file of a Macbeth color checker chart under uniform
> illumination, and identify the chart corners in the image.  From that, it
> creates a color mapping file you can use with pcomb to correct the image.
>
> However, it does not work very well for digital cameras.  You are much
> better off converting the RAW files directly using Dave Coffin's dcraw,
> which you can find on the web.  Getting to reflectance is more difficult,
> and depends on your situation.
>
> Check out the following if you haven't already:
>
>         http://radsite.lbl.gov/radiance/refer/sg96crs.pdf
>
> Cheers,
> -Greg
>
> > From: Jia Hu <hujia06 at gmail.com>
> > Subject: [Radiance-general] Reflectance meausrement using macbethcal
> utility
> > Date: July 29, 2014 8:22:08 PM PDT
> >
> > Hello,
> >
> > I am using Radiance macbethcal to estimate the material reflectance.  If
> I get the calibrated HDR image, how could I determine the RGB/reflectance?
>   Should  I pick a point in the generated HDR image to retrieve the RGB
> values, and then directly set the RGB to material RGB in Radiance?
> >  Is there any Radiance tool to directly obtain RGB value of a given
> pixel?
> >
> > Thanks,
> > Jia
>
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