[Radiance-general] Macbethcal Reflectances

[Gregory J. Ward]

Hi Marcus,

Without seeing your swatches or having a reflectance measurement to  
compare to, it's difficult for me to guess whether the calibration is  
working or not.  Certainly, the debug output from Macbethcal  
indicates that it was able to do a reasonable job of inverting your  
scanner's response.  However, it's still possible that some kind of  
auto-exposure is changing the results from one scan to the next, so  
it may be that your absolute levels are off.

-Greg

> From: "Marcus Jacobs" <marcdevon at hotmail.com>
> Date: December 23, 2005 10:44:09 AM PST
>
> Greg,
>
> I decided to go back and try to set up another calibration file. I  
> used the same steps that I used before. The software associated  
> with the flatbed scanner has no direct exposure controls, however  
> there is an option (which I select) to do no color correction.  
> This, I believe, prevents the enactment of the auto exposure  
> feature. Here are the results (debug.pic) from my latest scan  
> Macbeth color chart scan:
>
> http://i35.photobucket.com/albums/d178/marcdevon/ 
> MacbethColorChart_12212005002_templ.jpg
>
> As you can see, many colors were out of gamut however the white and  
> neutrals were able to be calibrated.  After running pcomb with my  
> color swatch, the reflectances were still high (0.80 < x < 0.95 on  
> a scale from 0 - 1). Here is the paint color swatch before  
> calibration:
>
> http://i35.photobucket.com/albums/d178/marcdevon/Behr_White_before.jpg
>
> and after calibration
>
> http://i35.photobucket.com/albums/d178/marcdevon/Behr_White_after.jpg
>
> I usually take the sample and the center of each. Do you believe  
> that the overall reflectances are valid or out of range?
>
> Thanks
>
> Marcus
>