Juan, PhotometricColorCalibration (PCC) appears to be similar to eXcalibrator.
You could have at least given shout-out to Bernhard Hubl, Mischa Schirmer and eXcalibrator for doing pioneering work in this area. eXcalibrator has been using APASS data for about a year and other catalogs since 2009.
It seems you have had a big change of heart. In August, of 2009, you completely dismissed eXcalibrator's methods as completely bogus. Now you have implemented something similar. Here is the first forum thread on eXcalibrator.
https://pixinsight.com/forum/index.php?topic=1378.msg7035#msg7035eXcalibrator has two methods. The classic calculation uses stars that appear white. The linear regression routine uses stars of almost any color. The routines return essentially identical RGB color balance factors.
The math for eXcalibrator "classic" is very simple. Given your teams excellent math capabilities, I suspect PCC is more sophisticated than eXcalibrator "classic" but maybe not for the linear regression routine. Also, I'm sure the user interface will have many "dials and knobs" for the user to fiddle with. Unfortunately, this may open the door for inconsistent results.
It will be difficult to determine if PCC gets better results than eXcalibrator, since there is no such thing as "true" color in astrophotography. The best we can do is get what we think is "reasonable" color and obtain consistent results.
Finally, I agree with Herbert. Please implement both the SDSS-DR7 & SDSS-DR9 catalogs. These data are more accurate than the APASS. Unfortunately, they only cover about 30% of the Northern Hemisphere.
Regards,
Bob Franke
developer of eXcalibrator
